Land Use

(These parameters apply to the Plant Growth Model Method.  For the Simplified Coefficient Method, see Simplified Coefficient Method, Land Use; for the Soil Moisture Method, see Soil Moisture, Land Use; for the MABIA Method see, MABIA Method, Land Use.)

Area

The land area for a catchment or subcatchment, or the share of land area from the branch above.  Note: You can use WEAP's Automatic Catchment Delineation to help you calculate catchment area.

Crops

Each catchment branch represents a piece of land on which exists an agricultural crop or other vegetation type .  For each branch, you need to specify which crop or plant (from the Crop Library) is planted.  This is most easily done using the Crop Scheduling Wizard.  Use the Crop Scheduling Wizard to choose crop and planting date, or choose one of the crop/planting dates already specified on another branch.  You may also specify if the planting and/or harvest dates will be a function of heat unit accumulation. There is also an option here to view or edit the Crop Library.  The expression created by the Crop Scheduling Wizard will use the CropLibrary function.  It is not possible to edit the expression directly in the data grid cell -- use the Crop Scheduling Wizard instead.

Surface Layer Thickness

This is the thickness of the top layer in the soil moisture model.  In order to properly simulate bare soil evaporation, it is recommended that the thickness of this layer be 10 cm (FAO 56).  Use of this parameter results in a default 13 layer model with the first layer thickness set in Surface Layer Thickness, the 2nd - 4th layers 100 mm thick, the 5th - 7th layers 200 mm thick, the 8th and 9th layers 300 mm thick, the 10th - 12th layers 500 mm thick, and the 13th layer 600 mm minus the Surface Layer Thickness.  This parameter must be blank if the Soil Layers parameter is used.

Soil Layers

This optional variable can be used to define the number and thickness of soil layers.  If blank, will default to 13 layers of increasing thickness (from top to bottom, in mm: 100, 100, 100, 100, 200, 200, 200, 300, 300, 500, 500, 500, 600) with a total of 3.5 meters.  Use the SoilLayers function to specify the thickness in mm, e.g., SoilLayers(100, 100, 200, 200, 300, 500, 600) would define 7 layers of increasing thickness from top to bottom with total = 2 meters.  Do not enter data for both Soil Layers and Surface Layer Thickness.

Soil Water capacity

This is the available water capacity, or the difference between the field capacity and the permanent wilting point.  This value is calculated by WEAP using the information entered into the Soil Library.  The soil associated with this sub branch is chosen in this field.  Click on the dropdown arrow and choose either "Enter Soil Properties directly" or "Choose from Soil Library."

Soil Albedo

The albedo of soil. This is used in the calculation of an average surface albedo, considering plant cover and soil, which is then used in calculating net radiation.

Soil Moisture Limit for Evaporation

Soil moisture limit to which bare soil evaporation can dry the soil.  This is expressed as a fraction of the soil moisture at wilting point.  A value of 0.5 is recommended.

Saturated Hydraulic Conductivity

The saturated hydraulic conductivity is a measure of a soil's ability to transmit water when subjected to a hydraulic gradient.  This value can be left blank if the Soil Water Capacity is being specified using the Soil Library.  In that case, the conductivity from the soil library will be used in the calculations.

Plant Uptake Compensation Factor

This factor allows deeper root zone layers to meet transpiration demand if upper layers are too dry.  If the value is equal to 1.0 then deeper layers can meet the demand.  If the value is 0.0 then deeper layers cannot be used to meet the demand.

Initial Soil Water Content

Value of the soil moisture content at the start of the model run for every layer in the soil moisture model.

Depth to Groundwater

This value is used to estimate the contribution of a shallow water table to crop transpiration and bare soil evaporation.  Leave this value blank if there is no  contribution from groundwater to ET.

See also: Plant Growth Model Calculation Algorithms

Entered on: Data View, Branch: Catchments, Category: Land Use, Tabs: Area, Crops, Surface Layer Thickness, Soil Water Capacity, Soil Albedo, Soil Moisture Limit for Evaporation, Saturated Hydraulic Conductivity, PLant Uptake Compensation Factor, Initial Soil Water Content, Depth to Groundwater.