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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #332167
Title: Hydrology submodel of WEPS

Author
item Fox, Jr, Fred
item DURAR, ABDU - City Of Manhattan, Ks, Public Works Department
item Skidmore, Edward

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/11/2020
Publication Date: 9/3/2020
Citation: Fox, F.A., A.A. Durar, and E.L. Skidmore. 2020. Hydrology submodel of WEPS. In: Tatarko, J., editor. The Wind Erosion Prediction System (WEPS): Technical Documentation. USDA Agriculture Handbook 727. United States Department of Agriculture, Agricultural Research Service, Beltsville, MD. p. 158-225.

Interpretive Summary:

Technical Abstract: The hydrology submodel of the Wind Erosion Prediction System (WEPS) models the movement of water within the atmospheric boundary layer and vadose zone. Inputs generated by weather generators as well as the crop growth, soil, management, and residue decomposition submodels provide inputs to the hydrology submodel. The hydrology submodel tracks the soil water content and temperature, with special emphasis on the water content at the soil-atmosphere interface, which is a significant factor in the wind erosion threshold friction velocity. The soil water content affects crop growth and residue decomposition. Changes in soil water content and temperature influence changes in the soil aggregate size distribution and soil aggregate stability, which are also significant factors in the erodibility of soil by wind. The hydrology submodel of WEPS maintains a continuous, daily, soil water mass and energy balance including a surface snow layer. Evapo-transpiration is partitioned into evaporation at the soil/snow atmospheric interface and crop transpiration, accounting for standing and flat crop residue evaporation suppression effects. Water flows modeled include rainfall, runoff, surface, and subsurface irrigation applications and drainage. Soil texture and bulk density are used to estimate soil hydraulic properties. Two methods of solving the soil water balance are implemented. In the first, the one-dimensional Darcy equation is applied to a thinly layered soil profile and solved as a system of ordinary differential equations. The soil water content at the soil-atmosphere interface is then estimated using the functional relationship between surface-soil wetness and the evaporation ratio. The second, faster, method uses the Water Erosion Predication Program (WEPP) hydrology model adapted to the WEPS modeling system. For this, the soil water content at the soil-atmosphere interface is estimated using the water content of a very thin surface layer. Using data from two field studies, the hydrology submodel of WEPS shows good results in estimating the susceptibility of the soil to wind erosion from a dry surface when configured to use the evaporation ratio with the one-dimensional Darcy equation method or when using the WEPP hydrology component. The one-dimensional Darcy equation method over-predicted the cumulative evaporation from the soil profile, limiting its usefulness for predicting crop available water after fallow periods. Use of the WEPP hydrology component for this purpose would give better results, although it under predicts the loss of water to evaporation during long periods without rainfall. Additional validation is recommended.