Start | Index | Overview • PREV | UP | * The SimComponent SlimWater estimates the daily change in soil water content in a variable number of soil layers based on the volumes of crop water uptake, soil evaporation, surface run-off and seepage below the root zone. Besides soil and weather input files, the SimComponent needs a separate input file (SlimProperties or SlimFile) where input parameters which are specific to the SimComponents SlimWater (and SlimRoots) are defined by the user.
CAUTION: It is important to note that the SimComponent does not consider canopy interception nor lateral subsurface run-off (interflow) in the water balance calculation. Soil water storage, surface run-off (WFAST), soil evporation (EVAPS), crop transpiration (EVAPC), water losses through mole drains (WDRAIN) and seepage (WSEEP) are calculated within the SimComponent, whereas potential soil evporation (POTES) and crop transpiration (PEVAPC) must be provided by other SimComponents (e.g. EvapTranDemand or CropEvapoTranspirationDualCoeff.java).
The water present in each layer is subdivided in different fractions. The fractions are defined according to the soil water content at certain soil matrix potentials for each soil layer: (1) SAT(i): Water content (m3 m-3) of saturated soil (SAT(i) at 0 kPa) (2) DUL(i): Water content (m3 m-3) at field capacity or Drained Upper Limit (DUL(i) at 33 kPa=0.33 bar=pF2.5) (3) AML(i): Water content (m3 m-3) at an intermediate soil water potential between field capacity (DUL) and wilting point (RLL) (AML(i) at 200 kPa=2.0 bar=pF3.3) (4) RLL(i): Water content (m3 m-3) at wilting point (RLL(i) at 1500 kPa). (5) SW(i): Initial soil water content at the start of the simulation (m3 m-3)
In relation to these cardinal points, different soil water fractions are calculated for each soil layer depending on their layer thickness (THICKL in m) : (1) Mobile water (mm): WM=(SAT(I)-DUL(I))*THICKL*1000 (2) Maximum retainable water (WRH in mm): WRH=(DUL(i)-RLL(I))*THICKL*1000 (3) Actual amount of retained water at the start of simulation (WR in mm): WR=(SW(i)-RLL(I))*THICKL*1000; and WR=<WRH (4) Half of the water retained at Wilting Point (WHT15R in mm): WHT15R = 0.5*RLL(I)*THICKL*1000 (5) Maximum amount of mobile water in the top soil layer which triggers run-off generation (WM1S in mm): WM11S=(SAT(1)-DUL(1))*THICKL*1000 (6) Fraction of water which is not available to solute transport (WRS in mm): WRS is set to WHT15R i.e. half of the water retained at wilting point (7) Fraction of water which is not available for upward movement of water and solutes in the topsoil layers (WFR in mm): WFR = (DUL(I)-AML(I))*THICKL*1000 (as defined in AFRCWHEAT 1995, not in Addiscott and Whitmore (1991)) (8) Fraction of water in finer pores (between 2 bar (pF3.3) and 0.5*Wilting point) available for upward movement (WR33 in mm): WR33 = (AML(I)-0.5*RLL(I))*THICKL*1000
NOTE: Due to various changes in the definition of AML(i), WHT15R, and WRS the definitions of WFR and WR33 and the equations for upward movement of water and solutes within the top soil layers may need substantial revision
The daily actual amount of water in each of the fractions in each layer is calculated depending on the amount of water input into the soil (rainfall or irrigation) and the water losses due to surface run-off, drainage (see function "LeachingWater()" and "RedistributionWithinLayers()"), soil evaporation (see function CalculateEvaporation()) and crop transpiration (function Avail() and TakeUp()).
Currently SlimWater does not account for crop canopy interception. However, when combining SlimWater with LintulDRUNIR.java or HillFlow1D.java, the interception can be obtained from these SimComponents.
Surface run-off (WFAST) is calculated as the excess of cumulative subdaily rainfall aliquots (WALIQ in mm) which exceed the water retention capacity of the first soil layer (WM1S). The parameter "CalcuationRunoffWater" is FALSE by default. Thus, in the SlimProperties file, the user must set "CalcuationRunoffWater" to TRUE in order to enable the calculation of WFAST. SlimWater breaks the daily amount of rainfall down into user-defined aliquots (WALIQ, default value: 3 mm). WALIQ is defined in the SlimProperties input file. Each aliquot is then added to the first soil layer and either added to the fraction of retained water (if WRH<WR) or to the mobile fraction (WM), until the infiltration capacity of the first layer (WM1S) is reached (WM1S=WM(1)). The excess water of each aliquot (WXTRA in mm) is then accumulated in a loop and constitutes the total daily surface run-off volume (WFAST in mm). NOTE: The amount of surface-runoff is highly sensitive to the ratio between the rainfall aliquot (WALIQ) and the thickness of the first soil layer (THICKL). In the original version of SLIM the default values for THICKL and WALIQ where 0.5 and 0.05m respectively. Thus a ratio of THICKL:WALIQ of 1:10 is recommended (Addiscott & Whitmore 1991).
The water (aliquot) which infiltrates into the first soil layer is routed vertically to the layers below. The water transport from one layer to the other consists of a vertical movement (see function LeachingWater()) of half of the product of the mobile water times a user defined fraction (SlimAlfa) from the upper layer to the lower layer. After a horizontal redistribution within the lower layer (RedistributionWithinLayers()), a second leaching of the remaining excess water from the upper layer occurs. This procedure tries to mimic the gradual vertical flow of water through the whole soil profile within one day. SlimAlfa is a critical parameter and is related to the clay content of each layer. Addiscott& Whitmore (1991) recommend for mineral soil layers the following equations to estimate SlimAlfa:
SlimAlfa = 1.0 when %clay <= 9.5 SlimAlfa = 1.0271-0.000302 * %clay when 9.5 < %clay < 58.3 SlimAlfa = 9.0 when %clay >=58.3
If the leached water reaches the last soil layer, the leachable fraction of the mobile water (WM*SlimAlfa) leaves the rootable zone and is thus added to the amount of daily seepage (WSEEP).
In addition, SlimWater considers the effect of mole drains on water losses through artifical drainage pipes (WDRAIN). In this case the user must specify the soil layer number (MD) where the drainage pipes are located in the SlimProperties file. Furthermore, the user must estimate in the SlimProperties file the fraction (DP in Decimal-%) of leaching water (WL) which is absorbed and evacuated by the mole drains in layer MD. If "CalculateRunoff" is switched off, then WXTRA is considered as preferential flow by-passing the main body of the soil. If this is the case, in addition to the fraction of the percolating water (DP of WL) the fraction DP of the preferential flow (fraction DP of WXTRA) is evacuated through the mole drains (WDRAIN). The remaining preferential flow in layer MD in each leaching loop (WXTRA*(1-DP)) is then added to the preferential flow.
If CalculateRunoffWater is FALSE:
\[ \begin{eqnarray} WDRAIN = WL(MD) \cdot DP + WXTRA \cdot DP \end{eqnarray} \]If CalculateRunoffWater is TRUE:
\[ \begin{eqnarray} WDRAIN = WL(MD) \cdot DP \end{eqnarray} \]Originally the subroutine of SLIM to calculate potential soil evporation received the potential open pan evaporation (EVAPO) from the subroutine EVAPW.FOR. Then potential crop transpiration (EVAPC) was derived from EVAPO by considering daily LAI of the crop and the light extinction coefficient. Finally, potential soil evaporation (POTES) was calculated as
\[ \begin{eqnarray} POTES = (EVAPO - EVAPC) \cdot 0.9 \cdot (1.0 - \frac {ECUM}{WRHTopsoil}) \end{eqnarray} \]| Content Type | Name | Description | Data Type | Unit | Min Value | Max Value | Default Value |
|---|---|---|---|---|---|---|---|
| constant | cALFA | The proportion of the mobile water in each layer that moves downwards to the underlying layer | DOUBLEARRAY | 1 | - | - | - |
| constant | cCalculateRunoffWater | If set to true runoff water (WFAST) is calculated, otherwise rain which exceeds infiltration capacity of the soil is by-passing the soil matrix | BOOLEAN | 1 | - | - | false |
| constant | cDP | The proportion of leaching water which is lost from layer MD (the layer : containing the drains) through mole drains | DOUBLE | 1 | 0.0 | 20.0 | 0.0 |
| constant | cELIM | Minimum daily soil evaporation (mm) from the topsoil layers within soil evaporation depth (MaxSoilEvaporationDepth) | DOUBLE | mm | 0.0 | 20.0 | 0.05 |
| constant | cIFWGEN | Switch to use estimates for initial soil water content in topsoil and subsoil (set to TRUE if initial water retention characteristics are unknown) | BOOLEAN | 1 | - | - | false |
| constant | cLatitude | Latitude | DOUBLE | ° | -90.0 | 90.0 | 50.7 |
| constant | cMD | Number of layer containing mole drains | INT | 1 | 0 | 1000 | 0 |
| constant | cMT | Number of layers in the topsoil | INT | 1 | 0 | 1000 | 5 |
| constant | cMaxSoilEvaporationDepth | Maximum soil depth which supplies water for soil evaporation | DOUBLE | m | 0.0 | 20.0 | 0.12 |
| constant | cSEEDD | Sowing depth in m | DOUBLE | m | 0.001 | 20.0 | 0.02 |
| constant | cSMD | Initial soil Moisture Deficit as estimated by the user (only used when initial soil water fractions are not provided); this initial soil moisture deficit is equal to the initial DEF value) | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| constant | cSoilLayerDepth | Depth of the bottom of each soil layer after soil layer transformation | DOUBLEARRAY | m | - | - | - |
| constant | cSoilWaterFieldCapacity | Volumetric soil water content of each layer at field capacity (pF2.5 or -33 KPa) | DOUBLEARRAY | m3/m3 | - | - | - |
| constant | cSoilWaterInitial | Volumetric soil water content of each layer at the start of the simulation | DOUBLEARRAY | m3/m3 | - | - | - |
| constant | cSoilWaterReducedThreshold | Volumetric soil water content of each layer at which water is available for upward movement (pF3.3 or 200 KPa) | DOUBLEARRAY | m3/m3 | - | - | - |
| constant | cSoilWaterSaturation | Volumetric soil water content of each layer at saturation (pF0 or 0.0 KPa) | DOUBLEARRAY | m3/m3 | - | - | - |
| constant | cSoilWaterWiltingPoint | Volumetric soil water content of each layer at permanent wilting point (pF4.2 or -1500 KPa) | DOUBLEARRAY | m3/m3 | - | - | - |
| constant | cWALIQ | The aliquot size in the rainfall splitting routine (mm) | DOUBLE | mm | 0.0 | 20.0 | 3.0 |
| constant | cWM1S | Amount if mobile water (WM) in the top soil layer at saturation (mm) | DOUBLE | mm | 0.0 | 20.0 | 10.3 |
| constant | cWMGENS | Default values for mobile water (WM) in the subsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 1.9 |
| constant | cWMGENT | Default values for mobile water (WM) in the topsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 2.75 |
| constant | cWRGENS | Default values for retained water (WR) in the subsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 11.6 |
| constant | cWRGENT | Default values for retained water (WR) in the topsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 9.1 |
| constant | cWRSS | the amount of water that is not available for water and solute transport in the subsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 7.15 |
| constant | cWRST | the amount of water that is not available for transport of water and solutes in the topsoil layers (only used if water retention characteristics are unknown) | DOUBLE | mm | 0.0 | 20.0 | 4.35 |
| input | iFRR | Root restriction factor for water uptake in each soil layer as affected by root age and root density (provided by SlimRoots) | DOUBLEARRAY | 1 | - | - | - |
| input | iMD95 | Number of deepest soil layer containing roots (provided by other SimComponents e.g. SlimRoots) | INT | 1 | 0 | 1000 | 0 |
| input | iPotentialTranspiration | Potential crop transpiration (provided by other SimComponents e.g. CropEvapoTranspirationDualCoeff.java) | DOUBLE | mm | 0.0 | 20.0 | - |
| input | iRAIN | Precipitation | DOUBLE | mm | 0.0 | 20.0 | - |
| input | iReferenceCropEvapotranspiration | Reference Evapotranspiration (ET0) provided by other SimComponents (e.g. ReferenceETHargreaves.java or ReferenceETPM.java | DOUBLE | mm | 0.0 | 20.0 | - |
| input | iWithCrop | Switch to indicate the days of the year where a crop is present | BOOLEAN | 1 | - | - | false |
| state | sCAPS | the proportion of the soil porosity likely to support upward (capillary) movement of solutes in each soil layer | DOUBLEARRAY | 1 | - | - | - |
| state | sCAPW | the proportion of the soil porosity likely to support upward (capillary) movement of water in each soil layer | DOUBLEARRAY | 1 | - | - | - |
| state | sCAW | Cumulative amount of rainfall | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| state | sCAWM | Total crop available water in the mobile fraction in each soil layer | DOUBLEARRAY | mm | - | - | - |
| state | sCAWMT | Total crop available water in the mobile fraction over the actual rooting depth | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| state | sCAWR | Total crop available water in the retained fraction in each soil layer | DOUBLEARRAY | mm | - | - | - |
| state | sCAWRT | Total crop available water in the retained fraction over the actual rooting depth | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| state | sCAWT | Total crop available water over the actual rooting depth | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| state | sDEF | Daily soil moisture deficit (Difference between Rainfall and (Transpiration+Soil evaporation)) | DOUBLE | mm | -2000.0 | 200000.0 | - |
| state | sECUM | Daily soil moisture deficit in the retained water fraction (WRH(I)-WR(I)) of the topsoil layer (i=0) in mm | DOUBLE | mm | -2000.0 | 2000.0 | - |
| state | sNNR | Number of successive days when 0.9*(potential soil evaporation) exceeds rainfall | DOUBLE | mm | 0.0 | 2000.0 | - |
| state | sSOILAV | Sum of soil available retained (SAWR) and soil available mobile (SAWM) water in each layer | DOUBLEARRAY | mm | - | - | - |
| state | sTWM | Total amount of mobile water over the soil profile | DOUBLE | mm | 0.0 | 200000.0 | 0.0 |
| state | sTWR | Total amount of retained water over the soil profile | DOUBLE | mm | 0.0 | 200000.0 | 0.0 |
| state | sTWRH | Total soil available water capacity over the soil profile | DOUBLE | mm | 0.0 | 200000.0 | 0.0 |
| state | sWFR | Amount of less mobile water in each layer not available for upward movement of solutes or water (DUL(i)-AML(i)) | DOUBLEARRAY | mm | - | - | - |
| state | sWHT15R | Retained water below 0.5*wilting point in each layer not available for movement of solutes | DOUBLEARRAY | mm | - | - | - |
| state | sWLM | Total amount of less mobile water (WR-WHT15R) in each layer (only used for solute transport) | DOUBLEARRAY | mm | - | - | - |
| state | sWM | Daily amount of mobile water (WM) in each soil layer (mm) | DOUBLEARRAY | mm | - | - | - |
| state | sWM1S | Amount of mobile water (WM) in the top layer at saturation (mm) | DOUBLE | mm | 0.0 | 20.0 | 10.3 |
| state | sWMBeforeLeaching | Daily amount of mobile water in each soil layer before leaching occurs | DOUBLEARRAY | mm | - | - | - |
| state | sWR | Daily amount of retained water (WR) in each soil layer (mm) | DOUBLEARRAY | mm | - | - | - |
| state | sWR33 | Amount of retained water in finer pores of each layer available for upward movement of solutes or water(AML(i)-WHT15R(i)) | DOUBLEARRAY | mm | - | - | - |
| state | sWRH | Retained water at field capacity in layer i | DOUBLEARRAY | mm | - | - | - |
| state | sW_out | Water leaving each soil layer by vertical drainage percolating to the layer below | DOUBLEARRAY | mm | - | - | - |
| out | ActualEvapotranspiration | Sum of 'Evaporation' and 'Transpiration' | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| out | ActualSoilEvaporation | Actual soil evaporation as affected by potential evporation and soil mositure in the upper soil layers | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| out | ActualTranspiration | Actual crop transpiration as affected by crop water demand (EVAPC) and crop available soil water (CAWT) | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| out | CumulativeActualSoilEvaporation | Cumulative soil evaporation over time | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| out | CumulativeActualTranspiration | Cumulative crop transpiration over time | DOUBLE | mm | 0.0 | 2000000.0 | 0.0 |
| out | DRYFAC | Dryness factor in each layer (input to SlimRoots) | DOUBLEARRAY | 1 | - | - | - |
| out | PotentialEvapotranspiration | Sum of 'Potential Transpiration' and 'Potential Evaporation' | DOUBLE | mm | 0.0 | 22.0 | 0.0 |
| out | PotentialSoilEvaporation | Potential soil evaporation (provided by other SimComponents e.g. CropEvapoTranspirationDualCoeff.java) | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| out | PotentialTranspiration | Potential crop transpiration (provided by other SimComponents e.g. CropEvapoTranspirationDualCoeff.java) | DOUBLE | mm | 0.0 | 20.0 | 0.0 |
| out | THICKL | Standardized thickness of soil layers (after soil layer transformation) | DOUBLE | m | 0.001 | 20.0 | 0.0 |
| out | TLW | Total water content over all soil layers (mm) | DOUBLE | mm | 0.0 | 2000.0 | 0.0 |
| out | TotalCropAvailVolumetricWaterContentFirstLayer | Volumetric total water content in the first soil layer | DOUBLE | m3/m3 | 0.0 | - | - |
| out | TotalCropAvailVolumetricWaterContentPerLayer | Volumetric crop available water content in each soil layer | DOUBLEARRAY | m3/m3 | 0.0 | 50.0 | - |
| out | TotalCropAvailWaterContent | Total crop available water over the actual rooting depth | DOUBLE | mm | 0.0 | - | - |
| out | TotalCropAvailWaterContentFirstLayer | Total crop available water content in the first soil layer | DOUBLE | mm | 0.0 | - | - |
| out | TotalCropAvailWaterContentPerLayer | Total crop available water per soil layer (mm) | DOUBLEARRAY | mm | 0.0 | - | - |
| out | TotalSoilAvailVolumetricWaterContentPerLayer | Sum of volumetric mobile and retained water in each layer | DOUBLEARRAY | m3/m3 | 0.0 | - | - |
| out | TotalSoilAvailWaterContentPerLayer | Sum of mobile and retained water in each layer | DOUBLEARRAY | mm | 0.0 | - | - |
| out | TotalVolumetricWaterContentFirstLayer | Volumetric total water content in the first layer | DOUBLE | m3/m3 | 0.0 | - | - |
| out | TotalVolumetricWaterContentPerLayer | Volumetric total water content in each soil layer | DOUBLEARRAY | m3/m3 | 0.0 | 0.6 | - |
| out | TotalVolumetricWaterContentUpperLayers | Volumetric total water content over the rooting depth | DOUBLE | m3/m3 | 0.0 | - | - |
| out | TotalWaterContent | Total water content over all soil layers (mm) | DOUBLE | mm | 0.0 | 1000.0 | - |
| out | TotalWaterContentFirstLayer | Total water content in the first layer (mm) | DOUBLE | mm | 0.0 | - | - |
| out | TotalWaterContentPerLayer | Total water content in each soil layer (mm) | DOUBLEARRAY | mm | 0.0 | - | - |
| out | TotalWaterContentUpperLayers | Total water content over the rooting depth in mm | DOUBLE | mm | 0.0 | - | - |
| out | WDRAIN | Daily amount of water lost through mole drains (only calculated if MD>-1) | DOUBLE | mm | 0.0 | 2000.0 | - |
| out | WFAST | If cCalculateSurfaceRunoff is TRUE: Daily amount of surface run-off (mm); If FALSE: WFAST is the infiltration excess water by-passing the soil matrix | DOUBLE | mm | 0.0 | 2000.0 | - |
| out | WSEEP | Daily amount of deep percolation (mm) | DOUBLE | mm | 0.0 | 2000.0 | - |
| out | WaterBalance | Daily Water Balance over the soil profile (mm) | DOUBLE | mm | -20000.0 | 20000.0 | 0.0 |