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Simulation of water flow in plant communities

1. Simulation of water flow in plant communities SPAC model description exercises and user s manual 2nd edition ater Henrik Eckersten Institutionen f r markvetenskap Avdelningsmeddelande 97 5 Avdelningen f r lantbrukets hydroteknik Communications Swedish University of Agricultural Sciences Uppsala 1997 Department of Soil Sciences ISSN 0282 6569 Division of Agricultural Hydrotechnics ISRN SLU HY AVDM 97 5 SE Denna serie meddelanden utges av Avdel ningen f r lantbrukets hydroteknik Sveriges Lantbruksuniversitet Uppsala Serien inneh ller s dana forsknings och f rs ksredog relser samt andra uppsatser som bed ms vara av i f rsta hand internt intresse Uppsatser l mpade f r en mer allm n spridning publiceras bl a i avdelningens rapportserie Tidigare nummer i meddelandeserien kan i m n av tillg ng levereras fr n avdelningen Distribution Sveriges Lantbruksuniversitet Institutionen f r markvetenskap Avdelningen f r lantbrukets hydroteknik Box 7014 750 07 UPPSALA Tel 018 67 11 85 67 11 86 This series of Communications is produced by the Division of Agricultural Hydrotechnics Swedish University of Agricultural Sciences Uppsala The series consists of reports on research and field trials and of other articles considered to be of interest mainly within the department Articles of more general interest are published in for example the department s Report series Earlier issues i
2. WATPOTGB WATPOTGR WATPOTGS Other States ACCBAL ACCINPUT ACCINTEV H Sensible heat flux to the atmosphere from soil surface Only used when the SOILWPOT switch I H Sensible heat flux to the atmosphere from wet leaf surfaces Hy Sensible heat flux to the atmosphere from dry leaf surfaces 8 Soil water content at saturation SOILWPOT switch 1 Only used when the ToT Temperature difference between wet canopy surface and ambient air TT Temperature difference between dry canopy surface and ambient air T Soil surface temperature Only used when the SOILWPOT switch Ty Temperature of wet leaf surfaces Tor Temperature of dry leaf surfaces 8 Soil relative water content root zone Only used when the SOILWPOT switch 1 8 3 Soil relative water content sub soil Only used when the SOP WPOT switch 1 s Soil relative water content soil surface Only used when the SOILWPOT switch I Er Potential transpiration only Ey values gt 0 are accumulated EEr Actual to potential transpiration ratio Fy Water uptake by root e Vapour pressure in the ambient air Saturated vapour pressure in the stomata cavities We Canopy water potential W Soil water potential used for the actual transpiration calculations Wn gt Upper limit for soil water potential in Brooks amp Corey relationship Only used when the SOILWPOT switch 1 Ya gt Soil wat
3. B Perttu K and Andersson J 1995 En introduktion till biogeofysik An introduction to biogeophysics Division of Agricultural Hydrotechnics Communications 95 6 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy AVDM 95 6 SE 72 pp in Swedish Eckersten H amp Kowalik P J 1986 Measured and simulated leaf air temperature differences in a willow stand In Eckersten H ed Willow growth as a function of climate water and nitrogen Department of Ecology and Environmental Research Swedish University of Agricultural Sciences Report 25 31 pp Eckersten H Kowalik P amp Lindroth 1986 Simulation of diurnal changes of leaf temperature transpiration and interception loss in willow energy forest In Institute of Water Engineering and Water Management Ed Hydrological processes in the catchment Cracow Technical University Volume 1 17 21 pp Eckersten H amp Lindroth A 1986 Vattnet fl dar i energiskogen Pilarna har det svettigt Uppsatser och Resultat Nr 53 Biomassa och Energi 4 Inst f r skogsteknik Sv Lantb Univ Garpenberg pp 19 21 Eckersten H Nilsson L O amp Perttu K 1984 Environment and production of energy forests Poster abstract In Proc from Bio Energy 1984 Goteborg Sweden Vasastadens bokbinderi Goteborg pp 38 Jansson P E 1991 Simulation model for soil water conditions description of the SOIL model Division of Agricultural Hydrotechnics Report 165 Dep
4. If SWRESCAN 3 greater or equal to 100 or GROWTH switch 0 than r should be given per units of ground surface Only used if IF SWRESCAN 3 1 or 100 fQy Lohammar eq fay dy exp e f W 21 RESCLOHA 1 di RESCLOHA 2 e MPa RESCLOHA 3 f MPa RESCLOHA 4 a RESCMAX roux Maximum value of stomatal resistance It equals the resistance per unit of sm leaf surface through cuticular Note if all separate stomatal functions used are given per units of ground surface Le all SWRESCAN 1 3 not equal to zero are greater or equal to 100 or GROWTH switch 0 then ru should be given per units of ground surface emar RESCMIN Iain Minimum value of stomatal resistance per unit of leaf surface s m Note If all separate stomatal functions used are given per units of ground surface i e all SWRESCAN I 3 not equal to zero are greater or equal to 100 or GROWTH switch 0 ru should be given per units of ground surface ru RESCRAD Coefficients for determining the stomatal resistance per unit of leaf surface as a function of incident shortwave radiation Note If SWRESCAN 2 greater or equal to 100 or GROWTH switch 0 then stomatal resistance should be given per units of ground surface r If SWRESCAN 2 1 10 100 Conductance is a polynomial function and r RJ 1 a boR eR If SWRESCAN 2 2 20 200 Resistance is an exponential function r R a exp b R c RESCRADQ a m s or a s m RE
5. Numbers of output variables to be presented numbers on the screen during the simulation e g 4200 means 4 X 2 T zero G and zero D variables lt 0 implies no plotting a Special These parameters are activating special options It includes sensitivity parameters names starting with S The value for no test is given in brackets The subscript denotes the original value Where both the relative and the absolute values are possible to change a constant value of the variable concerned can be chosen by setting the relative change to 0 His the value normally used RESAIRHV a 1 ny t gt The ratio between the aerodynamic resistance for heat and vapour RESAIRRI Ri Ri 0 Relative change of the Richardson number 0 implies Ri 0 i e no effect Only used if Start parameter SWRESAIR 1 RESPLANU Coefficients for determining the plant resistance as a function of root uptake rate previous time step Fylt 1 r Fy t 1 a exp b Fylt 1 trymin MAX Tmin MIN Tyg no RESPLANT RESPLANU 1 a MPa s m g RESPLANU 2 b m sg RESPLANU 3 ru MPa s m g RESPLANU 4 Not used SRESCGRO x y to W 1 Relative change of r y Only used if SWRESCAN S gt 0 SRESCRAD t R Yr R 1 Relative change of r R Only used if SWRESCAN 2 gt 0 SRESCTEM Tr 1 Relative change of r T Only used if SWRESCAN 4 gt 0 SRESCVPD R r o vpd 1 Relative change of r vpd Only used
6. Second edition 58 s Persson R ed Proceedings NJF seminar no 247 Agrohydrology and nutrient balances October 18 20 1994 Uppsala Sweden 111 s Alavi G Radial stem growth and transpiration of Norway spruce in relation to soil water availability Granens tillv xt och transpiration i relation till markvattnets tillg nglighet Licenciatavhandling 13 11 14s Johansson W amp Feilin O Biogas fran vall Teknik och ekonomi vid odling sk rd transporter ensilering samt r tning med tv stegsteknik 38 s Svensson E Linn r H amp Carlsson H Utv rdering av vaxtanalys i fabrikspotatis 53 s Andersson A Vattentillgangar f r bevattning i Kalmar lin I Litteratur versikt I Iniervjuunders kning r rande vattenmagasin 48 s Wesstr m I Best mning av markens salthalt genom m tning med konduktivitetssond 18 s Eckersten H Jansson P E Karlsson S Persson B Perttu K amp Andersson J En introduktion till biogeofysik 72 s Eckersten H Simulation of water flow in plant communities SPAC model description exercises and user s manual 49 s Nabieian F Simulering av vattenbalans f r energiskog p en torvmark 25 s Eckersten H Jansson P E amp Johnsson H SOILN model user s manual Version 9 1 93 s Eckersten H Jansson P E Karlsson S Lindroth A Persson B Perttu K amp Andersson J En introduktion till biogeofysik 2 a upplagan 110s Carlsson H Larss
7. 1991b 1 Daily maximum temperature 2 daily minimum temperature 3 Air humidity at time t 4 Air humidity at time t 5 Air humidity at time t 6 Global radiation 7 Wind speed 8 Precipitation 9 Soil water potential 10 Net radiation F the variable should be given in this position in the input file Variable Symbol Explanation Unit DNETRAD 7 R Net radiation above the canopy see parameter STNETRAD Wm DPREC 5 Precipitation or leaf wetness differs i Precipitation P To prevent interpolation between values of DPREC the values of the adjacent minutes must be zero mm min Gi If INTERCEPT switch 10 or 20 Leaf Wetness lt 0 9 is wet gt 0 9 is dry DRHUMAIR 2 h Relative humidity of the ambient air DSOLRAD 3 R Global radiation at the canopy top W m DTEMPAIR 1 T Temperature of the ambient air CC DWATPOTG 6 y Soil water potential see SOILWPOT switch MPa DWINDSP 4 U Wind speed in the ambient air m s XXXX PAR The parameter file is an ordinary DOS file with ASCIT characters All parameters and their actual numerical values should be included in the file If any parameter is missing in the file a message is displayed on the screen and a default value is selected from the SPAC DEF file New parameter files may be created prior the execution of the model using the EXECUTION WRITE command SPAC INI Initial values of state variables should be given here Els
8. Ecology amp Environmental Research Swedish University of Agricultural Sciences Report 25 38 pp Eckersten H 1986b Simulated willow growth and transpiration the effect of high and low resolution weather data Agricultural and Forest Meteorology 38 289 306 Eckersten H 1991a SPAC GROWTH model description Division of Agricultural Hydrotechnics Report 164 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy R 164 SE 36 pp Eckersten H 1991b SPAC GROWTH model User s manual Division of Agricultural Hydrotechnics Communications 91 4 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy AVDM 91 4 SE 31 pp Eckersten H 1995 Simulation of water flow in plant communities SPAC model description exercises and user s manual Division of Agricultural Hydrotechnics Communications 95 7 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy AVDM 95 7 SE 49 pp Eckersten H Jansson P E and Johnsson H 1994 SOILN model ver 8 0 User s manual Division of Agricultural Hydrotechnics Communications 94 4 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy A VDM 94 4 SE 58 pp Eckersten H Jansson P E and Johnsson H 1996 SOILN model ver 9 1 User s manual Division of Agricultural Hydrotechnics Communications 96 1 Dep of Soil Sci Swed Univ of Agric Sci Uppsala 93 pp REFERENCES 51 Eckersten H Jansson P E Karlsson S Lindroth A Persson
9. Myp Z Z t 1 z Z ris mr t 1 MepMax where MeRMax PwOslZ Zsyct Root zone water potential Wy 4 8 0 0 0 0 01 2 4 2 if 0 lt 0 0 Ve m Vint 1 8 0 8 8 0 0 1 Z 2 2 if 8 gt 0 0 where 6 Mgr Z Zsu P Wm w 8 6 Layer below root zone water balance ms qrs AMgrpepth Gross Ot where Gross Myp t 1 M pmax where Mopmax LACS 2 6 Special functions In this section alternative or complementary calculations are presented These are available in the model and normally activated using the switch named Special The stomatal resistance r can in addition to the subfunctions given in chapter 3 also be a combined function r R vpd of radiation and vapour pressure deficit vpd Different functions can be chosen The function is included among the other subfunctions Eqs 411 413 The aerodynamic resistance r is modified by a factor named the Richardson number Ri which accounts for the effect of thermal convection on the transport of heat and vapour in the air This factor is proportional to the gravitation force g the distance from the canopy top to the roughness height zy z and the temperature difference between the surface and the air T t T t means that the input value of the time step is used Normally it is very small Eqs 414 415 The displacement height z and the roughness length z used for calculating the aerodynamic resistance could
10. SMymoMylt 1 P P where Mymax MyioLAI P Pexp KpLAD wet surfaces Ry HrLE lt Apa Ty is determined where Ru Roy Myimax E Ep in Eq 313 but with 20 if my P P gt 0 r 0 and dry surfaces Ray Hy LE S Ava Tey is determined where Ryr Ryo Rar Er Er in Eq 313 but with if myrtP P gt 0 R LH Temax Fo My Mymax SPAC MODEL DESCRIPTION 11 2 5 Soil water The link of the soil water module to the plant part of the model is through the plant uptake as given by Eq 311 The soil water potential is simulated as function of water content of the root zone Eqs 365 6 In turn the plant affects the soil water content through input of water to soil throughfall Eqs 342 and 351 and output of water uptake Eq 361 and soil evaporation Eqs 354 356 The soil is divided into three layers The surface layer mys receives water through rain throughfall P and lose water through soil evaporation E to the atmosphere and percolation to the root zone qs_ x The root zone myr receives water from the surface layer and lose water through root uptake Fy and percolation to the layer below root zone qp_ The layer below root zone m receives water by percolation from the root zone and lose water through percolation or run off to layers below quos which are not represented in the model The amount of water in the root zone can also increase if the root depth increases Am rpepu Eq 362 Then water i
11. The name of the file is specified by the user the format should be similar as in the file for final values of state variables created by the model when the OUTSTATE switch is on OUTSTATE OFF no action Default ON final values of state variables will be written on a file at the end of a simulation The name of the file is specified by the user and the format is the same as used in the file for initial state variables see the INSTATE switch 32 SPAC USER s MANUAL a Model Specific DRIVANA 0 Driving variables are minute values Default Some of the minute driving variables in the input file are not available or wanted to be modified This option allow you then to make simple modifications of the following driving variables Soil water potential DWATPOTG parameters WSPSR and WSPSD and Net radiation DNETRAD parameter STNETRAD T used if SPECIAL switch i is ON For net radiation also when DRIVANA switch 2 Weather driving variables are daily synoptic values Those are used to calculate analytical minute values DRIVPREC The driving variable DPREC is the registration of precipitation rate see further DPREC l Default The the driving variable DPREC i is the registration of wet or dry canopy see further DPREC INTERCEPT No simulations of evaporation of intercepted water on leaf surfaces Precipitation is assumed to be zero Pink AAA AYO Evaporati
12. below holds for the SIMVB EXE version 1 4 program dated 1997 08 18 The description is taken from SOILN User s manual Eckersten et al 1996 and modified and shortened to fit this report The objectives of the SIMVB program are to enable the user to run the model technically in a simple way to give possibility of both a strict and flexible presentation of input and output of the model to enable a simple way of using the model as a tool for evaluation of possible changes in input calibration validation and to bring order to input and output files 5 1 How to run SPAC 3 Run under DOS Firstly we make a short summary of which programs and files that are involved when running SPAC under DOS program in an ordinary way The SPAC model is executed by the program file SPAC EXE There are some associated files to this program A help file with variable descriptions etc SPAC HLP a file with standard parameter values and other informations needed by the model SPAC DEF and a file including titles and units of the output variables SPAC TRA The model is run by using a program file named PREP EXE This program helps you preparing the simulation and make the simulation i e you can select parameter values input files simulation period etc The PREP program illustrates well the in and outputs of the model type for instance gt prep spac All information needed for PREP can be stored in a parameter file xxxx PAR file You can give instructio
13. good when the other flows are small as close to sunrise or sunset The variables determining the partitioning of solar energy between the latent and sensible heat fluxes are for instance wind speed air humidity and stomatal resistance The surface temperature T is adjusted so that the canopy energy balance is fulfilled The radiation energy exchange between canopy and the surroundings is the net radiation intercepted by the canopy R o which is the net radiation above canopy R minus the corresponding value below canopy The latter value is calculated according to Beers law using the radiation extinction coefficient x and the leaf area index LAI The energy balance is in addition to R also affected by the fluxes of sensible heat Hy and latent heat LE whereas storage of heat in plant tissues is neglected Eqs 320 322 The sensible heat flux is proportional to the difference between the surface temperature and the air temperature T divided by the resistance for flow of heat in the air which is assumed to be the same as for vapour r alternative exists see section on special functions The latent heat flux which is proportional to transpiration is created by the vapour pressure difference between the surface of the stomata cavities e and that of the surrounding air e having a relative humidity equal to h The air at the evaporating surfaces in stomata is assumed to be at saturation T is determined by changing its
14. if SWRESCAN 3 gt 0 SRESCWAT r wJt w EL Relative change of r y Only used if SWRESCAN I gt 0 SRESRADD 0 Forcalculation of stomatal resistance r as a function of stomatal resistance per unit leaf area and leaf area index LAD SRESRADD is the absolute change of LAT in this function Only used if GROWTH switch gt 0 SRESRADR 1 The same as for SRESRADD but the relative change of LAI Only used if GROWTH switch gt 0 STDENERG Au 0 1 Maximum allowed deviation in the canopy energy balance W m STDWATPO Sin 10 04 Maximum allowed change in the canopy water potential during a MPa time step of dt minutes SPAC USER s MANUAL 39 STNETRAD ag bg CR Coefficients in R agtb R c R determining net radiation above 0 canopy R as a function of DSOLRAD or DNETRAD OBS If cg lt gt 0 then should be ag bg 0 and vice versa STNETRAD 1 ag 23 0 W m STNETRAD 2 br 0 649 STNETRAD 3 cr 0 WATPOTCF Coefficients for determining water potential P as function of water content previous time step my t 1 Pm y t l Pema Pomax Pomin f where f expla x x 1 exp a 2 1 where X I my t I Vin ymax NOTUSED if a 0 WATPOTCE L a WATPOTCF 2 not used 40 SPAC USER s MANUAL 4 4 OUTPUTS Water Energy Atmosphere Atmosphere ere intevapo latheati latheatt senheati senhoa tt nr dcahi CE rer PLANTINT AT TEMPSURI TEMP
15. maximum amount of water possible to be retained by the unit leaf area myr Eqs 340 342 The intercepted water evaporates E in a way similar to that of the transpired water Ep after it has passed through the stomata Hence E is calculated using the same equations as for Ey but with the stomatal resistance r equal to zero Since the evaporation takes place during the same time step as the interception the reservoir for water on the canopy my often becomes zero already during the current time step Eq 345 Normally not the whole canopy is wet The canopy has a dry part LAI 1 my mypya and a wet part LAImy myma From the dry surfaces transpiration can continue whereas on the wet surfaces it stops The dry and wet surfaces have different energy balances since transpiration is retarded by the stomata resistance whereas the evaporation of intercepted water is not The fraction of total net radiation energy R available for transpiration is proportional to how large fraction of the canopy surface that is dry Less number of stomata can transpire therefore the stomatal resistance r increases in the same proportion as the available net radiation decreases The net radiation of the dry surfaces R and the increased r determines the temperature of the dry surfaces T r see Eq 320 For the wet surfaces the temperature Ta is determined by the net radiation R and the fact that r 0 Eqs 343 348 Siny P P E at
16. model Change the parameter value s as in 2 above and make a new simulation Repeat this until you are not able to get a better agreement between simulated uptake and measured sap flow Note that changes of parameter values should be realistic Consider first of all that leaf area index of a spruce stand of this type is about 8 or even more Changed parameters How and why Best simulation Tree I amp Tree 2 AO Al R2 n 6 Validation Select a new period and make a new simulation with the parameter values derived for spruce with help of the calibration above Describe the performance of the model Tree I amp Tree 2 AQ AL R2 n 30 SPAC SIMULATION EXERCISES SPAC USER s MANUAL This manual describes the SPAC model version 5 0 dated 951210 It is a shortened and revised version of the original SPAC User s manual Eckersten 1991b 4 1 Files amp input files XXXX BIN The driving variable file is a PG file The variables in the PG file can be organized in different ways depending on how different parameters are specified An ASCCT file should be converted to PG file before it can be used by the model use the PG program Two type of input files can be given Normally minute or about 10 minute values are given and then they should be given in the order shown in the table below In case daily values are given then the switch DRIVANA should be 2 and variables shoul be given in the following order see further Eckersten
17. out of water easily available for MPa transpiration WATPOTX Was Canopy water potential when plant water content is at maximum MPa Aerodynamic resistance RESAIRD Z Displacement height parameters should be set SWRESAIR and an RESAIRDO 0 RESATRH Zy Height for measurements of wind speed parameters should be set m SWRESAIR 1 and RESATRHO 0 RESAIRZ z Roughness length parameters should be set SWRESAIR I and RESAIRZO m 0 SWRESAIR Switch 1 Switch for chosing between two functions for the aerodynamic resistance r el r 1 h d z U 1 f LAD U f Resistance_stomata Parameters related to the resistance for vapour flow through stomata Special care should be taken as regards the units of parameters The units of the given functions refer to the leaf surface or the ground surface depending on the specification given by the User The stomatal resistance function is taken the highest value of those proposed by the different sub functions For selection of sub functions see parameter SWRESCAN RADRESR Rosin 3 R Remin gt R Tama This parameter is the radiation level below which W m the stomatal resistance r R is constant equal to its maximum value Only used if SWRESCAN 2 gt 0 SPAC USER s MANUAL 35 RESCGROU In analogy with RESCTEMP but SWRESCAN 4 replaced by SWRESCAN 5 O RESCLOHA Coefficients used for alternative stomatal functions Be aware of the units 0 Note
18. r is inversely proportional to the wind speed U measured at height zy r is expressed as a function of characteristic heights of the stand r decreases with the roughness height z and the displacement height z at which the logarithmic wind profile derived for the conditions above the canopy yields a wind speed equal to zero Eq 338 Fig 334 AG a ENTRE RR un Figure 334 Aerodynamic resistance Sine pi I T f I f as function of wind speed m A es 6 OA 1 07 oO Ji i 15 0 7 0 1 i Sk 1 0 35 0 1 S E 4 2 A o 10 constant value Xe max CRG TW r vpd Loins SEoMax where WC different functions see par RESCWAT r R different functions see par RESCRAD r vpd different functions see par RESCVPD r T LAI In zu Za Zo 10 SPAC MODEL DESCRIPTION 2 4 Rain interception A fraction of the rain falling on the canopy P is intercepted on the vegetative surfaces and thereafter evaporated to the air The rest P falls onto the ground and increases water content of soil The rain is assumed to be intercepted by the canopy in a similar way as the radiation This means that the fractional interception of the rain is the same for all sublayers of leaf area in the canopy Hence Beers law is used but instead of the radiation extinction coefficient we use the rain interception coefficient Kp The upper limit of water interception Myma is determined by the
19. the soil plant atmosphere system Background During night when it is dark stomata are closed and the plant does not transpire As the sun rises in the morning the solar radiation is absorbed by the leaves and stomata open The plant starts to transpire If the stomata of some reason do not open there will be less transpiration and leaf temperature will increase Monitoring this plant community by for instance remote sensing this increase in surface temperature could be observed It is far more difficult to measure how much the stomata resistance has increased However by using the SPAC model you could estimate how much it should have increased to give the observed temperature increase In the examples below you will be trained to derive properties of the plant like stomata opening from simulated output variables like leaf temperature transpiration etc I Make a reference simulation Start the SIMvb program Choose model SPAC application BGF course and exercise Ex2 Give inputs to the simulation Make the simulation Store the simulation Make use of the instructions in Exercise 1 above In the plant preparation option select Brassica Store the reference simulation so that you can compare it with later simulations f i as Store 0 2 Simulation with a plant with other properties You have another plant community which basically is of the same type as the one you stored as reference above However there is one prope
20. use SIMVB is also described in this report This model description section serves as a tool when using the model and then should be used together with the User s manual describing variables used in the program etc which is also included in this report The link between the model description and the manual is through the symbols see List of symbols As regards the validity of the model the reader is referred to other publications see list of references in which tests of different parts of the model have been made The software of the model is available from the author on request Since the model aims to be a research tool although hopefully suitable for many practical purposes it includes possibilities to choose among different hypotheses see the section on special functions and will be modified as research makes progress A section of the model description usually starts with a short general summary of its contents written in italics followed by a more detailed verbal and graphic description of the calculation procedure The section ends with the mathematical expressions The numbers given to equations figures and tables are related to the number of the subsection concerned SPAC MODEL DESCRIPTION The model is a transpiration model based on the Soil Plant Atmosphere Continuum SPAC concept simulating the flow of water from soil through the plant to the atmosphere The model is developed for crops but can be applied on other spec
21. AC SIMULATION EXERCISES Change parameter value GIVE INPUT Changes Parameters etc Select file ain_plan par Change parameter value Press Enter Save Make simulation View output and compare the results with the reference simulation Did the differences decrease Repeat this making new simulations with modified parameter values until no differences remain Note that the changes you introduce in ain_plan par remains until you choose Plant A in the normal preparation again 3 Document the results Answer the following questions Which parameter was changed Which value was achieved Explain how the differences between the simulated values of Plant_A and the reference plant could be explained by the differences in the parameter value 4 Plant B Examine differences between Plant B and the reference simulation Follow the instructions of 2 and 3 above 5 Plant C Examine differences between Plant C and the reference simulation Follow the instructions of 2 and 3 above SPAC SIMULATION EXERCISES 21 Plant_A E Plant B Plant_C 22 SPAC SIMULATION EXERCISES Exercise 3 Effect of sun elevation on evaporation Objectives To estimate how global radiation and net radiation change when the latitude change To estimate how the radiation change influence the evaporation and energy balance of a crop Background Solar radiation is the most important factor influencing proce
22. Pa Specific density of moist air 1204 7 gm Pe Density of bulk soil gm Py Specific density of water 1 10 gm 6 Soil relative water content root zone ys Soil relative water content of soil surface layer Ba Difference between 0 and relative water content at upper limit of Brooks amp Corey eq 6 Relative water content lower limit for use of Brooks amp Corey eq 8 Relative water content coeficient used for soil surface resistance estimates 6 Soil relative water content at saturation a Coefficient of saturated soil hydraulic conductivity gm s a bj c dj Coefficient names i t water use eff c r W d displacement height e saturated differs Ce vapour pressure h canopy height L L ohammar eq Li Lindroth eq o roughness height r r R R net radiation ra aerodynamic resistance ras within canopy aerodynamic resitance rp plant resistance rr soil root resistance rss soil surface resistance v r R vpd my plant water w analytic humidity b Root density resistance factor MPa Cyc Pore size distribution coefficient in Brooks amp Coreys eq Cy Soil pore size distribution factor C Specific heat per unit mass of air 1 004 Jg K e Vapour pressure of the air above canopy hPa E Evaporation rate of intercepted water gm s E Soil ground surface evaporation gm s a Saturated vapour pressure of the air hPa Cre Saturated vapour pressure of the air inside the s
23. SCAN 3 0 0 1 2 3 4 No Loham f R vpd f vpd Loham Cienciala v for r f T SWRESCAN A4 0 0 1 2 3 No Polyn Exp ln for r f y SWRESCAN S 0 0 1 2 3 No Polyn Exp ln SPAC USER s MANUAL 37 Plant resistance r Plant resistance from root surface to the mesophyll of leaves MPa s m g RESPLANT BW Soil root resistance RESGROA a Hydraulic conductivity of saturated soil g m s RESGROB b Factor related to the root density MPa RESGROC c Coefficient related to soil pore size distribution interception INTERCK Kp Rain interception coefficient related to leaf area PLANINTX myu Maximum amount of water intercepted per unit of leaf area index g m Growth EXTCRAD K Radiation 300 3000 nm extinction coefficient related to leaf area LAI LAI Leaf area index Soil water These parameters are used only if the SOILWPOT switch 1 BROOKPOR a Pore size distribution coefficient Brooks amp Coreys equation BROOKPSIA wy Air entry pressure Brooks amp Coreys equation MPa BROOKPSIX y Lower limit of water potential for use of Brooks amp Coreys equation MPa BROOKRES _ 6 Relative water content lower limit for use of Brooks amp Corey eq BULKDENS _ 9 Dry weight of soil per unit bulk volume m IRRIGPSI Soil water potential in root zone at which automatic irrigation should start MPa IRRIGWAT Water supplie
24. SCRAD 2 by or b RESCRAD 3 c or c s mv RESCTEMP Coefficients for determining the stomatal resistance per unit leaf surface as a 0 function of canopy temperature Note If SWRESCAN 4 greater or equal to 100 or GROWTH switch 0 than r should be given per units of ground surface r If SWRESCAN 4 1 100 Conductance is a polynomial function and r T J aytb T 40 7 If SWRESCAN 4 2 200 Resistance is an exponential function 1 T ar exp by T y d If SWRESCAN 4 3 300 Resistance is a logaritmic function rT ar In b Tte gt RESCVPD Coefficients used for alternative stomatal functions Be aware of the units 0 Note If SWRESCAN 3 greater or equal to 100 or GROWTH switch 0 than stomatal resistance should be given per units of ground surface r 36 SPAC USER s MANUAL RESCWAT SWRESCAN IF SWRESCAN 3 1 or 100 f Y Lohammar eq 1 vpd R c R a b vpd 1VR Note for f y see RESCVPDP IF SWRESCAN 3 2 or 200 r vpd R a b vpd c R 100 IF SWRESCAN 3 3 or 300 r vpd a exp b vpd c d IF SWRESCAN 3 4 or 400 Lohammar eq Cienciala vers 1 vpd R 1 g where 2 d c RAR a b vpd 1 RESCVPD 1 a W m or a s em or als m or a W m RESCVPD 2 b hPa or b s cm hPa or b hPa or b hPa RESCVPD 3 c s m or c cm s 107 0 01W or c hPa or cm s RESCVPD 4 d s m or d m sh Coefficients for determining the stomatal resistanc
25. SURT wet leaf dry leaf on plant precgrou g latheatg sonheatg Ai aa SC CWATS E PEER TA EE SES FPA AERA iaa Vv a sur TEMPSURG SOILWATR qsubroot soil surface qrootsub SOILWATB ai De stream Figure Schematic description of the SPAC model Solid lines are flows of water or energy For explanation of variables names see list below All units expressed per unit of area refers to the ground surface Note that units of output variables sometimes are multiples of the basic SI system Variable Symbol Explanation Unit States PLANTWAT my Exchangeable water in canopy g m PLANTINT my Water intercepted on the canopy gm SOILWATB m Soil water content of sub soil below root zone Only used when g m the SOILWPOT switch 1 SOILWATR mx Soil water content of root zone Only used when the gm SOILWPOT switch 1 SOILWATS my Soil water content of surface layer Only used when the gm SOILWPOT switch 1 Flows INTEVAPO E Evaporation of intercepted water g m s IRRIGABO Irrigation supplied above canopy gm s IRRIGGRO Irrigation supplied on soil surface g m s PREC P Precipitation above canopy g m s PRECGROU P Amount of water from precipitation falling to the ground m s SPAC USER s MANUAL 41 QROOTDEP QROOTSUB QROOTSUR QSUBLOSS QSUBROOT QSURROOT SOILEVAP TRANS Auxilaries BOWEN LAL LATHEATG LATHEATI LATHEA
26. TT NRADABOV NRADCAN NRADCANI NRADCANT NRADGROU RESIAIR RESICAN RESICGRO RESICRAD RESICTEM RESICVPD RESICWAT RESIGROB RESIGROR RESIGROS 42 AMeanepn gt Change in water in the root zone due to increased root depth Gaon gt Percolation of water from root zone to sub soil Only used when the SOILWPOT switch 1 Gps Capillary rise of water from root zone to surface layer Only used when the SOILWPOT switch 1 toss gt LOSS of water from sub soil Only used when the SOILWPOT switch qg gt Capillary rise of water from sub soil to root zone Only used when the SOILWPOT switch 1 Qs gt Percolation of water from surface layer to root zone Only used when the SOILWPOT switch 1 Es Soil evaporation Only used when the SOILWPOT switch 1 Er Transpiration Bowen ratio H LE or H LE When the INTERCEPT switch 2 this ratio concerns the whole canopy LAI Leaf area per unit of ground surface leaf area index LE Latent heat flux to the atmosphere from soil surface Only used when the SOILWPOT switch 1 LE Latent heat flux to the atmosphere from wet leaf surfaces LE or Erp Latent heat flux to the atmosphere from dry leaf surfaces R Net radiation of the site n R Net radiation of the canopy Ry Net radiation energy available for the energy balance of the intercepted water Only used when the INTERCEPT switch 2 Rar Net radiation energy available f
27. ambient air The flow is retarded by the resistances of stomata r and the air outside the leaf r As the plant loses water from its maximum value Mymax the canopy water potential y drops below that of the soil y This difference is the force for uptake of water Fy against the resistances of the soil r and the plant r Each unit of leaf area can maximally contain my amount of easily exchangeable water corresponding to a maximum water potential Yemas When the reservoir is emptied the canopy water potential is Womine The difference in plant water content m during a time step t is calculated with a procedure described by Kowalik amp Eckersten 1984 Eqs 310 313 dbmy Fy E at E20 where Fu Yr W O yt Wo Yema Pomar Yomin I my My max Mymax My LAI SPAC MODEL DESCRIPTION 7 2 4 Canopy energy balance The radiation energy absorbed by the canopy is used for the evaporation of water from the plant The evaporation rate latent heat flux is also determined by other factors and often during day time more radiation is absorbed than is needed to meet the energy demand by evaporation Then the canopy surface becomes warmer than the ambient air The excess heat is leaving the plant through the sensible heat flux During night or at rainfall normally the opposite occurs We assume that the energy storage rate in leaf tissues is negligible in comparison with the other flows This assumption is perhaps not so
28. be set proportional to the height where the wind speed is measured zy q 418 419 In the original version of the model the aerodynamic resistances for heat and vapour are given equal values The resistance for heat r u could however be divided by a factor a as compared to that for vapour r Eq 419a SPAC MODEL DESCRIPTION 13 The net radiation above canopy R should be an input variable However this variable is often lacking and then it can be estimated from the global radiation above canopy R Eq 420 r R vpd different functions see par RESCLOHA 412 n 1 1 10Ri 414 where Ri g y Talty T T 4273 15 U 415 Za Ager 418 Zo Aghy 419 ty t a 4 l 9a R agRy by 420 4 SPAC MODEL DESCRIPTION SPAC SIMULATION EXERCISES Exercise 1 introduction to a simulation model SPAC Objective The aim of this exercise is to give you some answers to the following questions What is a simulation model How is it used technically What is the structure of the SPAC model How does the most essential water dynamics of a plant work A simulation model what is that I will try to answer that question shortly by describing some used terms A basic problem that we will try to solve is What is the effect of weather on plant water dynamics To answer this question we must have an idea of how the plant interacts with its environment In this case the plant and its su
29. by the radiation energy available the drying power of the air and several factors regulating the flow of water from the plant to the atmosphere The loss of plant water is compensated by the uptake of water from the soil which however for several reasons can be delayed or is too small to meet the transpiration demand If for instance the soil water availability is small then the plant water reservoir decreases The plant then clos s its stomata and the transpiration decreases and the plant can stabilize its water status on a new lower level During the night the stomata are closed and the plant loses water only very slowly through the cuticle Then the plant can recover to a plant water status close to that of the soil The flow of water is described in terms of water potentials and resistances 2 1 Plant water The amount of easily available water is proportional to the leaf area It is decreased by transpiration but increased through the root uptake created by the differences in water potentials of the plant and the soil A closed canopy typically contains much less exchangeable water than is lost and gained daily through transpiration and uptake Hence the water reservoir is replaced several times a day There is a reservoir of easily available water in the plant my from which water can be transpired p The driving force for transpiration is the vapour pressure difference a between the air inside the stomata cavities and the
30. d application one way of running these versions and to store them separately is to do as follows 1 Store the main application with a full set up of input files under XXXXXAN NA as usual 2 Store the files changed due the specific version under a separate directory named fi VERSION I Le NA WERSION 1 Do not change the name of the files and remember to store the INFO LIS file in which you give an identification of the application stored on the directory 3 Copy files from VERSION directory to working directory by pressing Prep from SubDir this option is available if Teacher ON is selected under Help etc MAIN MENU 48 SIMVB MANUAL 6 LIST OF SYMBOLS Symbol Description Unit Ya Water potential corresponding to air entry pressure MPa We Canopy water potential MPa Vins Minimum and maximum canopy water potential MPa WeMax W Soil water potential MPa Wy Soil water potential at upper limit of Brooks amp Coreys eq MPa 5 Generally used for a difference during a time step Slope of saturated vapour pressure curve in Penman eq Pa C mMax Maximum allowed deviation in canopy energy balance Wm Anne Change of water in the root zone due to increased root depth gm s AV Max Maximum allowed change of Y from one iteration to another for accepting the water balance MPa Y Psychrometric constant 67 Pa kK K Radiation extinction coefficient related to leaf area Kp Rain interception coefficient related to leaf area
31. d through irrigation g m s IRRIGSUR Fraction of irrigated water supplied below canopy directly to soil surface RALA Ags Coefficient for determining the aerodynamic resistance as function of leaf s nr area index RESGROBG b Factor related to resistance aginst water flow in bulk soil Similar to MPa RESGROB however without influence of root density ROOTDEP z Rootdepth should be positive m RSSCOEF a gt Coefficient for soil surface resistance proportional against the inverse of s m relative water content RSSEXP by Coefficient for determining soil surface resistance exponential for the relative water content RSSTHETA 6 Coefficient for determining soil surface resistance SOILDEP z Depth of whole soil volume should be positive Gn SURDEP Zsy Depth of surface layer from which soil evaporation takes place should be m positive THETADM _ 8 Difference between soil water content at saturation and at the situation when soil water potential equals air entry pressure 38 SPAC USER s MANUAL THETAS 0 Soil relative water content at saturation 5 Plotting_on_ line Variables can be plotted on screen during the simulation by selecting appropriate values on XTGD and PMAX Using this option version of model is written on screen PMAX plot maximum 1000 The expected maximum value among the variables differs selected by XTGD XTGD variables plotted on screen 4000
32. dy have made a complete preparation and want to have free access to any part of the program you select Check off The Check option only checks the order in which you select options in the program from preparation to presentation of output during one run If you leave the program the Check option is reseted The program itself enables a good overview of the principal way of using the model If a complete run GIVE INPUT Simulation etc has been made the different options in the schedule in principal can be chosen in any order at any time However for the first run you have to choose them in the following order i GIVE INPUT Copies input files to the working directory Note that the routines under this option overwrites files at the working directory without warnings ii SHOW INPUT Variables in input file named AIN_CLIM BIN are presented iii SIMULATION The results are stored in files named SPAC_CUR bin and SPAC_CUR sum CUR denotes the current simulation iv SHOW OUTPOT Variables in SPAC_CUR bin are presented Variables that are presented are grouped in accordance to subjects You can also compare results with the previous run and or simulations that have been stored see below You can view the summary file of the simulation as well v Store files Here you can store the simulation results SPAC CUR under a different name You can also recover a previous stored simulation to the name SPAC_CUR thereby mak
33. e per unit leaf surface as a function of canopy water potential Note If SWRESCAN 1 greater or equal to 100 or GROWTH switch 0 than r should be given per units of ground surface r If SWRESCAN 1 100 Conductance is a polynomial function and arbre dw rev OBS y is in units of 0 IMPa If SWRESCAN 2 200 Resistance is an exponential function r Cy a exp b w d OBS y is in units of MPa RESCWAT E alm s or als ma RESCWAT 2 b or b MPa RESCWAT 3 c or c MPa RESCWAT 4 d or d s m RESCWAT S e switches for choosing arbitrarily among different stomatal resistance functions r f R or and y or and vpd R or and T or and y Polyn polynomial function for conductances Exp exponential function for resistances Loham Lohammar equation Layers canopy is divided into layers of unity leaf area in each layer the resistance is the maximum value given by all resistance functions used if not Layers function is used then canopy resistance is the stomatal resistance divided by the leaf area index If SWRESCAN is multiplied by 100 i e equal to 100 200 300 400 etc than the input functions on stomatal resistance are assumed to be expressed per units of ground surface r see RESCWAT RESCRAD RESCVPD for r fQy SWRESCAN 1 1 0 1 2 No Polyn Exp for r f R SWRESCAN 2 1 0 1 2 10 20 No Polyn Exp Polyn layersVExp layers for r f R and or vpd SWRE
34. e they are zero SPAC USER s MANUAL 31 E Output files SPAC FIN Final values of state variables SPAC_NNN bin Output variables are stored in a PG structured where NNN is the current number of simulation The file is a binary file to be used by the PGraph program for plotting results from the simulation The file can be converted to ASCII format by using the PG program SPAC_NNN SUM Contains a summary of all inputs used by the simulation and a summary of simulated results The first part of this file until the sign corresponds to a parameter file This means that you can repeat the simulation by renaming this file to a file with extension PAR 4 2 SWITCHES The purpose of switches is to chose the simulation mode Most switches could either be OFF or ON Others can achieve different values E Technical CHAPAR OFF Parameter values are constant during the whole simulation period Default Parameter values may be changed at different times during the simulation period If editing directly into parameter files the time of change and the new parameter values should be specified after the other parameter values valid from the start of the simulation A maximum of 20 time points can be specified INSTATE OFF The plant water is set initially so that the leaf water potential equals the soil water Default potential All other state variables are initially zero Initial values of state variables will be read from a file
35. er potential in sub soil simulated Only used when the SOILWPOT switch 1 Y Soil water potential in root zone simulated Only used when the SOILWPOT switch 1 Wes 3 Soil water potential in surface layer simulated Only used when the SOILWPOT switch I Water mass balance check Zacc Input Accumulated input of water to the system If SOILWPOT switch 0 P F If SOILWPOT switch 1 P Lace Accumulated intercepted evaporation SPAC USER s MANUAL MPa s m g m W m W m W m g m C CC CC CC C vol vol vol g m s gm s hPa hPa MPa MPa MPa MPa MPa MPa g m g m gm d 43 ACCOUT ACCSTORE ACCTRANS ACCTRPOT PLANTWAP Other Flows DELTAPLA DELTAPLP Output Accumulated output of water from the system If SOILWPOT switch 0 E4P If SOILWPOT switch 1 B B pos Total storage of water in the system If SOILWPOT switch 0 mytmy If SOILWPOT switch 1 mytmyrtms Lre Er Accumulated transpiration Zacc Erp Accumulated potential transpiration my Exchangeable water for the potential transpiration my Exchangeable water in canopy my Exchangeable water for the potential transpiration 44 g m gm d gm d g m d g m gm s g m s SPAC USER s MANUAL SIMVB MANUAL The description
36. ies as well The basic version of the model was described by Turner amp Kowalik 1983 and Kowalik amp Eckersten 1984 The model Fig 300 consists of four compartments one for easily available water located in the leaves one for intercepted water on the canopy surface one for soil water available for plant uptake and for soil water available for soil evaporation The model simulates flows and states on a ground surface basis and assumes horizontally uniform stands in terms of the model parameters The time step of the water submodel is 1 4 minutes Input data are minute values on global radiation net radiation air temperature air relative humidity wind speed and precipitation registered above the canopy Alternatively daily values on soil water potential can be used as input instead of being simulated Also daily values of the weather driving variables can be used by choosing special functions generating minute values of temperature air humidity etc Water Energy Atmosphere Atmosphere 2 nb et 0 dE y g root zone soil surface m sub soil 9 SEE Os Rent Loss VD stream Figure 300 Schematic description of the SPAC model Solid lines are flows of water or energy For explanation of symbols see text and list of symbols 6 SPAC MODEL DESCRIPTION The leaves contain water which is easily available for transpiration The transpiration occurs during day time when stomata are open and the rate is determined
37. ing it available for use in the presentation options etc vi EXIT the program You exit the program by pressing the EXIT bottom on the main menu 5 2 Alternative use of SIMvb Help Documentaion and description of variables are available under several options in the program H Give comments By putting the mouse arrow on space between boxes and by making a click on the right bottom you can give comments on whatever you want The comments should be stored or cancelled MAIN MENU immediately after they have been given 46 SIMVB MANUAL Type of User Youcan select three type of users Student Teacher Research under Help etc MAIN MENU Different users will get access to different parts of the SIMvb program E Edit files You can change a single parameter or initial state value by select GIVE INPUT and Parameters Be aware of that you should write the parameter variable name correctly As concerns changes in parameter files Note that changes of parameter values preferably are introduced in the AIN_MAN PAR since values in this file have the highest priority if you make a change in AIN_PLAN PAR and the parameter name also appears in AIN_MAN PAR the latter holds Note that in initial state file at least the first position on a row should be an empty space then write name space and value 2 Use PREP program manually The PREP progam can be run in a standard interactive way within SIMvb If you have made Preparat
38. ion the prepared AIN_xxxx PAR files are read by PREP The files are read in the following order AIN_SOIL PAR AIN_PLAN PAR AIN_OUT PAR AIN TIME PAR AIN MAN PAR Simulation results are stored in SPAC_ cur bin as in the normal simulation If you do not want to load the parameters files you have chosen with GIVE INPUT then select One par file only and Check off under Help etc MAIN MENU before entering PREP Note that output file now is named SPAC_xxx bin where xxx is a number from 001 999 and if you want to make use of presentation of output options it has to be restored to SPAC_cur bin use Store files MAIN MENU Use PG program manually The PG program can be used in a standard interactive way within SIMvb SIMvb brings you only to the proper file Select PG ON under Help etc MAIN MENU E Use Excel program manually In case Excel is loaded and there is a path to it the Excel program can be used in a interactive way within SIMvb Select Excel ON under Switches etc MAIN MENU SIMvb converts the PG binary file concerned to dbf or lotus 123 format and brings you automatically into Excel With help of the presentation routines of SIMvb you can select variables to be exported to Excel Using only one parameter file There are two possibilities to run SIMvb with only one parameter file one 1 is to completely govern the simulation with a single parameter file and the other 2 is to still make use of output routi
39. isplacement height Are there other properties that differs and what are the effects of them First store the results from the forest simulation in 2 above Change parameter values GIVE INPUT Changes Parameters etc Select file ain_plan par Change parameter value Press Enter Save Make a simulation Compare the results with previous simulations for the forest and the crop Which were the effects of the introduced parameter changes Were they larger or smaller than in 2 above What are the reasons for the effects Give answers to these questions below OS AS AAA AA RT NA ARGS PUD dr mm LA AA OAS are care NEUTER et SPAC SIMULATION EXERCISES 29 4 Compare the simulated uptake with measured values for sap flow in spruce First you have to get access to the measured sap flow data Choose GIVE INPUT Validation Sap flow Then you can compare the simulated values with the measured ones by choosing SHOW OUTPUT Validation Give a description of how well your simulation fitted measured data Both in your own words and in terms of statistical values Tree 1 amp Tree 2 AQ AL R2 n 5 Calibration Above when simulating the forest you changed only the plant structure However other properties will also differ compared to a crop Which ones do you think Select those properties that you think will improve your plant uptake predictions Express the properties in terms of parameters of the
40. iven by initial values which are input to the model In case a flow variable depends on the state variable that it changes there is a feedback in the system It is a positive feedback if an increase in the state variable increases the flow into it There is an unstable situation between state and flow In the opposite case we have a negative feedback and a self regulating situation increased state decreases inflow All these calculations can theoretically be made by hand However for practical reasons we make use of a computer since there is an enormous amount of calculations to be made Summary The system is represented by the model The model has a boundary The conditions at the boundary change with time and are model input represented by driving variables The structure of the model is built up of state and flow variables At start of simulation the state variables are given by initial values The flow variable changes the state variables The flows are determined by the processes of the system Processes are represented by equations and parameters Properties of the system are represented by parameter values The objective of using a simulation model differs As aresearch tool it is used to evaluate hypotheses about interactions in nature and to get ideas for setting up new hypotheses As an education tool it is used to illustrate dynamics in nature which of practical reasons otherwise are not possible to st
41. mainly two processes estimation of soil water potential in the root zone and soil surface evaporation Both processes are based on information taken from the SOIL model Jansson 1991 which is a model representing soil in much more detail Hence the modifications of the original description of the SPAC model mainly concern i including a soil water module ii taken away the description of the GROWTH submodel ili renaming parameter and variable names used in the computer and iv adjust symbols to basically follow Rosenberg et al 1983 and Eckersten et al 1995 In addition some new parameters of the model are described However note that the parameter listis not complete in this report A more popular description of SPAC ver 5 0 written in Swedish is included in Eckersten et al 1995 The report also includes a section for exercises specially designed for studying the dynamics of the SPAC model These exercises have been used in courses in biogeophysics in 1993 and 1994 at the Swedish University of Agricultural Sciences and have been developed in collaboration with teachers and students of the courses Special acknowledgements are given to Elisabet Lewan Anders Lindroth Emil Cienciala Karin Blomb ck and Jennie Andersson at the Swedish University of Agricultural Sciences Uppsala These exercises are run with help of aWINDOWS based program named SIMvb which is a further development of SOILNvb described by Eckersten et al 1994 How to
42. n results in a file that isnot overwritten Store Files by new simulations Current to Store i Store O After going through this procedure once you can select any option at any time In many cases you come to a sub menu when choosing an option You go back to the main menu by closing the sub menu x in upper right corner If you for some reason happen to leave the SIMvb program you can enter the program without repeating all preparations etc Restart the program and select model application and exercise concerned After that choose Check off Then you have access to earlier made preparations and current previous and stored simulations For further information see the SIMvb description below Simulation exercise Run the program according to the instructions given above Select a Sunny day and answer the following questions 1 Which parameter groups exist in the model SPAC SIMULATION EXERCISES 17 2 Which are the driving variables 3 Make the simulation 4 Which are the state variables that describes the storage of water 5 Which are the flows of water to the state variables and from them 6 Make a picture of how the state and flow variables are connected di SPAC SIMULATION EXERCISES RAR RO D DAS PAL PT naiean 7 Store the simulation SPAC SIMULATION EXERCISES Exercise 23 Plant Objective To illustrate the effects of plant properties on water and energy dynamics in
43. n the Communica tions series can be obtained from the Division of Agricultural Hydrotechnics subject to availa bility Swedish University of Agricultural Sciences Department of Soil Sciences Division of Agricultural Hydrotechnics P O Box 7014 S 750 07 UPPSALA SWEDEN Tel 46 18 67 11 85 46 18 67 11 86 SPAC model description exercises and user s manual end edition Henrik Eckersten Institutionen f r markvetenskap Avdelningsmeddelande 97 5 Avdelningen f r lantbrukets hydroteknik Communications Swedish University of Agricultural Sciences Uppsala 1997 Department of Soil Sciences ISSN 0282 6569 Division of Agricultural Hydrotechnics ISRN SLU HY AVDM 97 5 SE Table of Contents I PREFACE int ne oran nas es SPAC MODEL DESCRIPTION sus TERENE ERI 6 2 1 Plant water ss PAE EET E EA 7 2 2 Canopy energy balance ssesressessein A AA E E w 8 2 3 Resistances remote AE seoapedabehtoateites aeiaai 9 2 4 Rain interception EE EN EE ET 11 2 5 Soil water ss PEE EE A NPA EEEE EEA 12 2 6 Special functions Ser AE PAE 13 SPAC SIMULATION EXERCISES RE AE ASE TTT EAAS gt IS Exercise 1 Introduction to a simulation model SPAC eessen 15 Exercise 2 Plant EEE AR EAT Sih INA ol NS SE ET 20 Exercise 3 Effect of sun elevation on evaporation eeseresecserrerre 23 Exercise 4 Effect of plant structure on evaporation and energy XCHARE on retenu I 21 SPAC USER
44. n to the ground gm s Loss of water from soil through percolation and runoff gm s Loss of water from surface layer to root zone gm s Loss of water from root zone to soil layer below root zone gm s Aerodynamic resistance sm Aerodynamic resistance specially for heat sm Aerodynamic resistance from soil surface to above canopy sm Stomatal resistance per unit ground surface sm Sub function of the stomatal resistance only dependent on the canopy water potential sm Sub function of the stomatal resistance only dependent on the water potential in the root sm zone Sub function of the stomatal resistance dependent on the radiation and vapour pressure sm deficit of the air sm Sub function of the canopy resistance dependent on the radiation Sub function of the stomatal resistance only dependent on the canopy temperature sm Sub function of the stomatal resistance dependent on the vapour pressure deficit of the air sm Maximum stomatal resistance sm Minimum stomatal resistance sm Soil root resistance MPa s m g Soil surface resistance sm Richardson number p Net radiation above canopy Wm Net radiation of the canopy Wm Net radiation of soil surface Wm Net radiation of the wet and the dry part of the canopy respectively Wm Plant resistance MPa s m 8 LIST OF SYMBOLS F Stomatal resistance per unit leaf area sm R Incident radiation intensity 300 3000nm on a horizontal surface W m Romin Radiation limi
45. nes of SIMvb so that presentations programs can be used in a normal way In case of 1 store the file under name AIN_ONE PAR and select switch one par file under Help etc MAIN MENU In case of 2 store the parameter file under the name AIN_MAN PAR and take away i the declaration of file names except for FILE 9 which should be named ain_fert bin if it is used and ii the OUTFORN switch All the other parameter files have to exist but could n be empty except for a at the end of the file ain_out par is delivered by SIMvb automatically SIMVB MANUAL 47 BR Making the five parameter files Under the option GIVE INPUT Normal MAIN MENU the five parameter files ain_soil par ain_plan par ain_out par ain_time par and ain_man par can be created automatically from the last simulation i e from SPAC_CUR SUM file mE Multiple runs Up to 6 multiple simulations can be done and plotted It is the presentation of output that limits the number of simulations A Initial states of previous run Make a simulation using outputs of the previous simulation as initial states in the new simulation 8 File fist In the GIVE INPUT option of SIMvb files can be selected arbitrarily by selecting file list in the list menus This is a complement to the other preparation options Alternative applications under directory KXXX Often several versions of the same main application is wanted to be run by SIMvb Using the Standar
46. new simulation including the estimated change in radiation GIVE INPUT Changes Variables Remember to change both global and net radiation 3a First examine the changes in energy exchange in more detail Give the changes between the new simulation and the previous one choose the way to compare yourself Variable Change Equation Factor s mainly responsible for the approx change Refer to the equation and explain why net radiation sensible heat flux latent heat flux leaf temperature On a daily basis are the canopies warmed or cooled SPAC SIMULATION EXERCISES 25 3b Sum up using your own words the important changes in both energy exchange and water conditions and give an explanation to them 4 Effect of changed climate on plant water and energy conditions For latitude 40 N not only the global radiation changes As a consequence of the different global radiation also other weather variables will differ we continue to assume optimum soil water conditions First you change the weather factor you want to change GIVE INPUT Changes then you make new simulations and compare the results with other simulations to answer the following questions Which weather factor s have you changed How Give an explanation of why this these variables should be changed Describe and give an explanation of the important changes of water and energy conditions Compare with the case when you only changed
47. nly used if SPECIAL switch 1 SOILWPOT 0 Soil water potential is input given in the driving variable file Default Soil water potential is simulated Note that still the variable nr 6 in driving variable must exist although not used SPECIAL OFF Parameters in the group Special are NOT available Default Parameters in the group Special are available These parameters enables modifications or introduction of special functions normally kept fixed or not used No water flow simulations are made I Actual canopy evaporation Er and or simulations are made Default SPAC USER s MANUAL TRANSPPOT No calculations of the potential transpiration Ey 1 The potential transpiration E defined as the transpiration being independent of the Default plants internal water status i e my myy is simulated using the iteration method for solving the canopy energy balance The potential transpiration E is defined as the water content is non limiting and located on the leaf surface i e surface resistance r 0 4 3 PARAMETERS Note that the units sometimes are multiples of the basic SI system Variable Symbol Explanation Unit i Plant water PLANWATX my Maximum available plant water per unit of leaf surface gm WATPOTGP Yp 3 W for the potential transpiration MPa Only used if TRANSPPOT switch gt 0 WATPOTN Yann Canopy water potential when the plant is
48. ns to PREP to take the information from that file PREP is the program thatcan activate SPAC EXE i e to start the simulation Output from the simulation are stored in two files SPAC_001 BIN and SPAC_001 SUOM The first file BIN includes the values of the simulated variables The second file SUM includes both a summary of all outputs averages sums etc and the prerequisites for the simulation i e the inputs which can be used to repeat the simulation if it is renamed to xxxx PAR You can get presentations of the results and make further evaluations of the simulation outputs SPAC_001 BIN with help of a special program PG EXE Run under WINDOWS SIMvb The principal idea of programming SIMvb is to make use of already developed DOS programs and applications The programming is restricted to this administration of the operative programs and routines SIMvb EXE is programmed in Windows VisualBasic and is possible to run under WINDOWS if the VBRUN300 DLL file is available You start SIMvb from the run option of WINDOWS or by double click on the icon if installed or by writing under DOS gt win simvb SIMVB MANUAL 45 In the program SIMvb you always start with the bottom denoted Start here Note that in the SIMvb program you should always use only single click Then you select model to be used and then application which should be stored on a hard disk or floppy Thereafter you normally continue with GIVE INPUT If you alrea
49. nt of light In the model the degree of light dependency is represented by parameters Hence parameter values represent plant properties and normally differ between plant types A parameter value is normally independent of time If it is not its variations is an indication that the model is not general in some way SPAC SIMULATION EXERCISES 15 The result of the model concerns a certain time interval If the time step is one minute as it is in the SPAC model the calculations of for instance the transpiration concerns the evaporation from leaves to the atmosphere during the last minute Similarly the uptake calculations concerns the amount of water taken up by roots during the last minute These two variables are called flow variables and transport water from the plant and to the plant respectively In this way they determine the amount of water stored in plant which is called a state variable and is the base for the calculations of flows during the next minute The model calculates the flows to and from the state variable which then changes minute by minute We could say that the model imitate the plant development This type of model we call simulation model The state variable is hence the amount of water that exists at a certain occasion The unit is independent of time and is the mass divided by a reference area gH O m The flows which change the state over time are expressed in gH O m s At the start of a simulation state variables are g
50. of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy R 165 SE 72 pp Kowalik P J amp Eckersten H 1984 Water transfer from soil through plants to the atmosphere in willow energy forest Ecological Modelling 26 25 1 284 Kowalik P J amp Eckersten H 1989 Simulation of diurnal transpiration from willow In K L Perttu amp PJ Kowalik Editors Modelling of energy forestry Growth water relations and economy Simulation Monographs Pudoc Wageningen pp 97 119 Kowalik P J amp Turner N C 1983 Diurnal changes in the water relations and transpiration of a soybean crop simulated during the development of water deficits Irrig Sci 4 225 238 Rosenberg NJ Blad BL Verma SB 1983 Microclimate the biological environment Second edition John Wiley amp Sons New York Chisester Brisbane Toronto Singapore 495pp 52 REFERENCES F rteckning ver utgivna h ften i publikationsserien SVERIGES LANTBRUKSUNIVERSITET UPPSALA INSTITUTIONEN F R MARKVETENSKAP AVDELNINGEN FOR LANTBRUKETS HYDROTEKNIK AVDELNINGSMEDDELANDE Fr o m 1994 94 1 94 2 94 3 94 4 94 5 95 1 95 2 95 3 95 4 95 7 95 8 96 1 96 2 96 3 97 1 97 2 97 3 97 4 97 5 Tabeli L Tj le i torvjord 46 s Halldorf S Runoff water as a soil forming factor in arid zones 62 s Jansson P E SOIL model User s Manual Third edition 66 s Eckersten H Jansson P E amp Johnsson H SOILN model User s manual
51. on K amp Linn r H Vaxtniringsstyrning i potatis 69 s Uppenberg S Waligren O amp Abman M Saturated hydraulic conductivity in an acid sulphate soil A minor field study in the he Vietnamese Mekong delta 45 s Djodjic F Avrinningsmonster i ett litet keromr de under 40 r av successiv urbanisering 38 s Vukovic M The effect of soil hydraulic properties on ground water fluctuations in a heavy clay soil Measurements and simulations 43 s Eckersten H Jansson P B Karlsson S Lindroth A Persson B Perttu K Carlsson M Lewan L amp Blomb ck K En introduktion till biogeofysik 3 e upplagan 130s Eckersten H Simulation of water flow in plant communities SPAC model description exercises and user s manual 2 edition SPAC version 5 0 52 s
52. on between latitudes at noon is related to the difference in latitude A suggestion is that you start by calculating the sun declination Make use of the Figure below At noon the sun elevation is at maximum and for August 13 in Uppsala it is 45 SPAC SIMULATION EXERCISES 23 North Equator Sun declination Sun elevation at noon August 13 at 40 N Estimate with help of Beer s law and Lambert s cosine law the global radiation at Uppsala and then the corresponding value for 40 N assuming the same turbidity as in the air above Uppsala Sun Above atncephare Re Solar constant R Solar radiation at ground surface but perpendicular against the sun arrays R Global radiation B Sun elevation x 10 m 100 km shortest distance between soil surface and the upper boundary of the atmosphere x length of the pathway of the sun arrays through the atmosphere K 0 22 10 m extinction coefficient related to x What is the relative change in global radiation What is the relative change in global radiation only caused by a decreased pathway for sun arrays through the atmosphere 24 SPAC SIMULATION EXERCISES 2 Reference simulation for Uppsala Make a reference simulation and store the results so that you can compare future simulations with this one see Exercise 1 3 Effect of changed incoming radiation on the energy balance transpiration and plant water storage Make a
53. on of intercepted water E and transpiration E are NOT going on simultaneously First the intercepted water is evaporated until the canopy is dry no transpiration occurs Then the transpiration starts Evaporation of intercepted water E and inspiration By are going on simultaneously The total canopy net radiation R is shared between the two processes in proportion to area of the two surfaces The intercepted water receives my Myintax fractions of Ry and the water for transpiration the rest The stomatal resistance is increased linearly towards ru when the fraction of dry surface decreases IRRIGAUT 0 No irrigation Default Automatic irrigation starts when soil water potential becomes lower than a critical value IRRIGPSD The concept is taken from the SOIL model Jansson 1991 SPAC USER s MANUAL 33 34 PENMANM I Default Evaporation simulations are made using an iteration method for solving the canopy energy balance Evaporation simulations are made using the Penman Monteith equation for calculating the latent heat flux and the energy balance The simulation time decreases RESCANOP 0 Default Different stomata resistance sub functions are combined by selecting the one with highest value Different stomata resistance sub functions are combined by adding them Only used if SPECIAL switch 1 Different stomata resistance sub functions are combined by multiplication O
54. or the energy balance of the water lost as transpiration Only used when the INTERCEPT switch 2 R Net radiation at the ground surface ng r Aerodynamic resistance T Canopy stomatal resistance per unit of ground surface r Qy Leaf stomatal resistance as a function of water potential in the root zone r R Leaf stomatal resistance as a function of incident shortwave radiation on the leaves r CE Leaf stomatal resistance as a function of canpoy temperature r vpd Leaf stomatal resistance as a function of vapour pressure deficit r y Leaf stomatal resistance as a function of canopy water potential a Soil resistance against water transport in sub soil Tyg Soil resistance against water transport in root zone r s gt Soil resistance against water transport in surface layer gm s g m s g m s gm s g m s g m s gm s gin s Qn m W m W m W m Wm W m W m W m Wm ism smh sm s nv s m s m s nv MPa s m 9 MPa s m g MPa s m g SPAC USER s MANUAL RESIGROU r i Soil root resistance between soil and root surface ROOTDEPTH z Root depth SENHEATG SENHEATI SENHEATT SOILWATRS TEMPDIFI TEMPDIFT TEMPSURG TEMPSURI TEMPSURT THETA THETASUB THETASUR TRANSPOT TRANSRAT UPTAKE VPRESAIR VPRESSUR WATPOTC WATPOTG WATPOTGM
55. rrounding is our system The system is limited in space it has a boundary The boundary conditions is here the situation in the atmosphere weather These conditions vary with time and are input to the model given by driving variables We have sorne ideas of how weather influences soil and plant These ideas are our conceptual model which often is clear in structure and theory but normally not possible to evaluate in detail or comparable with measurements in a systematic way The formalised model is based on the conceptual model The theory of the conceptual model is formalised in terms that can be evaluated quantitatively A theory expressed in words for instance when the atmosphere is dry the evaporation from the wet leaves is high should be expressed in precis terms How dry is the air How wet are the leaves How is vapour transported from the wet leaves to the dry air All these things must be expressed in quantitative terms The formalised model we call a mathematical model or here only model The model represents a system including several processes going on simultaneously The processes are represented by equations for instance how the stomata of the leaves open when light fall an the leaves The reason for the opening is that light causes chemical reactions in the grid cells This is a rather general rule for plants and can be represented by one type of equation However the degree of opening differs between species given a certain amou
56. rty that differs from the reference plant The aim of this exercise is to examine which property this is by analysing differences in transpiration water uptake plant water status radiation absorption sensible and latent heat fluxes and leaf surface temperature compare to the reference plant Note that there is one precise answer in terms of which property parameter value that differs Try to find this answer and explain how you could derive it from the analysis of differences in transpiration uptake etc i e from differences in output variables Simulation with a plant with other properties Give new inputs to the simulation Only one modification is needed compare to 1 above In the plant preparation option choose Plant_A Make a new simulation View output and compare the results with the reference simulation SHOW OUTPUT Select file f Store 0 Plant water flow fi FU uptake Make notations of differences in output variables Analyse with help of the model description what could be the reason for the differences Which parameter could be the reason for the difference Make a simulation with changed parameter values Make a change of the value of the parameter you expect to be the reason for the differences you found above Make the change so as to give the same result as the reference simulation i e try to eliminate the differences compared to the reference simulation Do it this way 20 SP
57. s MANUAL sssrovsrovoosreroees Un MN Ee oer TORRY 31 AFFIES guss air seen ens eolerstnttarpeeiseagetenvers TT 31 4 2 SWITCHES siennes eee ST ES Te 32 4 3 PARAMETERS PLAN ATOS VTT TT RE Es 35 Be SOP UMTS nn ns se 41 SIMVB MANUAL oossmsssrerorsooreseresre E haa ese eee 45 5 HOW torun SPAC a St tiens 45 5 2 Alternative use of OLNEY asiosio iniiis Radar 46 6 LIST OF SYMBOLS PT Ne 49 7 REFERENCES asie PESTE TE ETETE TETE EST TETE EE TEE IEEE IT IESTIETESTI SET EETT ET EETITIE 1 PREFACE This is the second edition of this report Compared to the first edition Eckersten 1995 the sections on SPAC simulation exercises and SIMvb manual have been updated The model description is only partly updated The newest version of the model version 5 1 dated February 1997 includes capillary rise of soil water which is updated in the description of model outputs chapter 4 but not described in the model equations chapter 2 This report is especially designed for courses in biogeophysics Two previous published reports SPAC GROWTH model description Eckersten 1991a and SPAC GROWTH user s manual Eckersten 1991b are shortened and put together This report also describes a new subroutine for soil water dynamics added to the SPAC model version 5 0 dated 951205 The main objective of introducing the soil module is to get the model more pedagogic in terms of representing a complete water balance of the site The soil water module includes
58. s taken from the layer below If the thickness of the surface layer za is larger i e deeper than the root depth z no root uptake occurs If no surface layer exists no soil evaporation occurs The loss of water through percolation is the amount of water that is in excess of the amount of water at saturation M sma Mgrmax ANd Mypmmo respectively defined as the relative water content at saturation 8 multiplied by the depth of the layer concerned and the density of water py Near saturation soil water potential in the root zone is a linear function of the relative water content 0 which is related the bulk density of soil p Eq 366 At all other occasions it is a non linear function given by Brooks amp Corey relationship Eq 365 Soil surface evaporation E is determined by Penman Monteith equation assuming the storage of heat in soil being neglectable in the energy balance The aerodynamic resistance r is increased in proportion to leaf area Eq 355 and the surface resistance r is inversely related to the relative water content of the surface layer 0 5 Eq 356 Soil surface water balance ms P Qs r Eg 0t where qsar mys t I Mygmax where Masmax PW OZsuet Soil evaporation B 8 AYL HE Ts where Las Lt a LAI Pers brss Lys ars O ps O di where LAS Mas ZsuriPg 12 SPAC MODEL DESCRIPTION Root zone water balance 5m grt AMenepth Grop Fy St where AMyrpepth
59. sses on earth It varies a lot between different latitudes For instance how much more solar radiation do surface receive on latitude 40 for instance Italy compare to here in Uppsala 60 Why is the radiation higher in Italy Is it because the sun beams reach the soil surface at a different angle or is it because the sun beams have a shorter pathway through the atmosphere If the plants in Sweden would receive as much radiation as in Italy just for a day how would that influence transpiration But of course if we consider longer time periods than one day the climate should change due to the high radiation level Which other weather variables would also change And what would then be the effect on transpiration The exercise is divided into four parts 1 estimate the change in radiation conditions in Uppsala 60 N if the sun elevation would be the same as for latitude 40 N corresponds to Italy 2 estimate the plant water and temperature conditions during a sunny day in August in Uppsala 3 and 4 estimate the change in plant water and temperature conditions due to the changed radiation climate nuances 1 Estimate the change in radiation due to latitude change Estimate the difference in global radiation between the latitudes by estimating how it differs under clear sky conditions at noon First you have to know the sun elevation at 40 N Estimate this by making use of the fact that the difference in sun elevati
60. t below which the stomatal resistance achieves its maximum value Wm t Time differs t Time at the beginning of a time step s b Time at the end of a time step s T Air temperature C To Ter Canopy surface temperature of wet and dry surfaces a T Canopy surface temperature C k t at start of simulation day number Ta Soil surface temperature C U Wind speed above canopy ms vpd Vapour pressure deficit of the air hPa Zy Depth of whole soil profile m Za Displacement height m Zo Roughness height m Ze Root depth m Zsuf Depth of soil surface layer m Zy Height above ground of wind measurements above canopy m 7 REFERENCES Papers and reports published with relevance for the SPAC model and publications referred to in the text Burujeny M 1992 Dygnsvariation i bladvattenpotential hos raps och senap M tningar och simuleringar Examensarbete Division of Agricultural Hydrotechnics Communications 92 3 Dep of Soil Sci Swed Univ of Agric Sci Uppsala ISRN SLU Hy AVDM 92 3 SE 27 pp Cienciala E Eckersten H Lindroth A H llgren JE 1994 Simulated and measured water uptake by Picea abies under non limiting soil water conditions Agric and Forest Meteor 71 147 164 Eckersten H 1985 Transpiration of Salix simulated with low and high time resolution weather data Research Reports Biotechnical Univ E K of Ljubljana Suppl 10 pp 49 55 Eckersten H 1986a Willow growth as a function of climate water and nitrogen Department of
61. the radiation VA AAN AD ONE N EAA use VARA tudes 26 SPAC SIMULATION EXERCISES Exercise 4 Effect of plant structure on evaporation and energy exchange Objectives Estimate how wind speed above the canopy differs between an agricultural crop and a forest Estimate how the difference in plant aerodynamic properties influence evaporation and energy balance of the plant Estimate how large the influences due to the aerodynamic properties are in comparison with other differences between an agricultural crop and a forest Estimate properties that can explain differences in uptake rates of a crop and a spruce stand Background The transport of heat and vapour in the air is related to the wind Close to the canopy wind is disturbed by the roughness of the surface Turbulence occur whichis very effective in transporting vapour and heat The degree of turbulence depends on how rough the surface is Is the forest more rough than an ordinary agricultural crop Is there some measure for this difference How will this difference in surface structure influence the plant energy and water conditions This exercise will try to answer this later questions It will also ask you for other differences between a crop and a forest in terms of properties that determine the water dynamics By considering the most important differences you might predict the water uptake by spruce You can check how well you succeed by comparing your simulated results
62. tomata cavities hPa Ep Transpiration rate gm st Er Potential transpiration rate gm s Fy Water uptake by roots gm s g Gravitational acceleration ms h Relative air humidity above canopy H Sensible heat flux from wet canopy to the air Wm LIST OF SYMBOLS 49 LAI Myg MyBMax Mer MyrMax Mys Moesmax My Myr My imax Myo My max Myo P P Gloss sor Gro Ye rY LR vpd r R rT r vpd Tomax Tomin Te 50 Sensible heat flux from ground surface to the air Wm Sensible heat flux from dry canopy to the air Wm Number of water balance iteration number von Karman s constant 0 41 Latent heat of water vaporisation 245 1 8 Jg Leaf area per unit ground surface leaf area index Water in the layer below root zone gm Water in the layer below the root zone at saturation gm Water in the root zone gm Water in the root zone at saturation gm Water in the soil surface layer gm Water in the soil surface layer at saturation gm Easily exchangeable water in the plant gm Water intercepted on the canopy surface per unit ground surface gm Maximum water intercepted on the canopy surface per unit ground surface gm Maximum water intercepted on the canopy surface per unit leaf area gm Maximum easily exchangeable water in the plant per unit ground surface gm Maximum easily exchangeable water in the plant per unit leaf area gm Precipitation above canopy gm s Precipitatio
63. try of the root system The resistance increases with decreasing unsaturated hydraulic conductivity a ly which in turn decreases faster with decreasing soil water potentials y when the soil pore size factor c is high as for sandy soils for instance Eq 330 Fig 331 50 Be A NR RANA Figure 331 The soil root resistance oh cS a eo ee Bocas p as function of the soil water potential a 2 r MPosm q he 3 cS Lae rO Olet Soil water potential MPa The plant resistance r is assumed to be constant Eq 331 SPAC MODEL DESCRIPTION 9 The stomatal resistance of the whole canopy i e per unit ground surface r is affected either by the incoming short wave radiation R the canopy water potential w or the vapour pressure difference of the air vpd e e Three separate mechanisms are assumed to regulate stomata one represented by r R one by r w and one by r vpd The actual value of r is then the highest value given by the three functions The User can choose which of the functions that should be active If the User gives the resistances per unit leaf area the stomatal resistances are assumed to be coupled in parallel with each other i e the stomatal resistance is inversely proportional to the leaf area index Note that in the program alternative ways of combining these functions are available also more sub functions are available Eqs 332 337 The aerodynamic resistance
64. udy because the resources are limited Both already known processes and purely theoretical processes can be studied this way As a forecast tool it is used to evaluate the effect of known or possible changes of the system properties or of changes in the boundary conditions on a certain variable for instance the transpiration How to run the model Start the SIMvb program From WINDOWS you start the model by making a double click on the icon for SIMvb if there is an icon otherwise you use the run option under Archive by starting c simvb exe simvb3 exe Note that within the SIMvb program only single clicks are used 16 SPAC SIMULATION EXERCISES Select exercise Start by pressing then select model then select application then select exercise Atypical procedure to make a simulation Select first initial loading of the application Select input data to the simulation Start here SPAC BGF course Exl fi GIVE INPUT Initial prep GIVE INPUT Normal Soil fi Clay Plant f i Brassica Weather fi Sunny day Management f i No irrigation SHOW INPUT View parameters Select file fi PARAMET txt Weather fi Air temperature SIMULATE Normal SHOW OUTPUT an example Select file No comparison Plant water flow Et transp View input data Make a normal simulation View the results of the simulation Store the simulatio
65. value using iteration until the sum of all three fluxes is below a certain limit Apa which is close to zero Eqs 320 322 324 Rie Hy LEy lt Anas T is changed until this statement is fulfilled where Ry R Ci exp KLAD Hy 0 0 TT Fa PC Ces Ca Ep esse meant YE Lea ex aexp b T c d T e T T 4273 15 Cu g he es aexp b T c d T e T T 273 15 8 SPAC MODEL DESCRIPTION 2 3 Resistances The pathway for water flow from bulk soil to the atmosphere is represented by four resistances the soil root resistance r from the soil where the water potential is Y to the root surface the plant resistance r from the root surface to the mesophyll of leaves the stomatal resistance r from the leaf mesophyll to the air just outside the leaf surface and finally the aerodynamic resistance r from close to the leaf surface to the ambient air above canopy The resistances vary with environmental conditions of the air and the soil as well as with the plant conditions If for instance the wind speed or the radiation or the soil water potential increases then the resistance against water flow decreases Fig 330 Atmosphere Figure 330 Schematic description of T 2 ae ee E the pathway for water from soil through the plant to the atmosphere For explanation of symbols see text The soil root resistance r is proportional to the root density factor b which accounts for the geome
66. values Start SIMvb select model SPAC application BGF course and exercise Ex4 and make initial preparation GIVE INPUT Initial prep Select input for the simulation GIVE INPUT Normal Soil Clay Plant woe Brassica Weather Sunny day Management No irrigation Change parameter values to those you estimated above GIVE INPUT Changes t Parameters etc Select file ain_plan par Change parameter values RESAIRH RESAIRD RESAIRZ Press Enter Save Make a simulation for the crop Store the results 28 SPAC SIMULATION EXERCISES Change parameter values again now to those of the forest Change the wind speed according to the ratio between forest and crop which you estimated above GIVE INPUT Changes Variables Wind speed Give the relative difference Note that this change remains until you make a new normal preparation of Weather Make a simulation for the forest Compare the results between forest and crop and describe the important differences and the reason for them 3 Sensitivity test Other differences between crop and forest Evaluate the effects of other differences between agricultural crops and forest Crops and forest differ in more aspects than the aerodynamic properties like for instance leaf area index etc What are the effects of a change in such a property compared to the differences in roughness length and d
67. with measured data on sap flow in spruce The exercise is divided into six parts 1 Estimate the parameters for plant structure that determine wind speed above the canopy 2 Compare simulated evaporation and energy exchange between the plant and the atmosphere for two plants one with aerodynamic properties of an agricultural crop and one with those of a forest 3 Evaluate the relative importance of differences in aerodynamic properties compare to other differences between crops and forest 4 Compare the simulated water uptake with measured sap flows 4 Calibration of the SPAC model 5 Validation of the SPAC model 1 Estimate plant properties and wind speed la Describe the surface properties of the different plant types Do this by estimating the parameters in the logarithmic wind profile equation Assume the crop to be I m high and the forest to be 20 m high Under which circumstances can the logarithmic wind profile law be used to determine the wind speed above the canopy Surface properties of the crop Surface properties of the forest SPAC SIMULATION EXERCISES 27 forest ree U wind speed m s 1b Estimate the wind speed 2 m above the canopies if the wind speed at 100 mis 5 ms Equation Wind speed 2 m above the crop Wind speed 2 m above the forest Ratio between wind speed above forest and crop U forest U crop 2 Make simulations with the estimated

Simulation of water flow in plant communities

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