Measured and Simulated Surface Soil Drying

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Abstract
The USDA initiated the Wind Erosion Prediction System (WEPS) to develop improved technology for predicting wind erosion. A HYDROLOGY submodel has been developed for WEPS to simulate the soil energy and water balances. This study was conducted to evaluate the performance of the HYDROLOGY submodel in predicting surface soil drying. Water content was measured gravimetrically in a bare 5‐ by 30‐m plot for 14 d after irrigation during July and August 1991. The plot was located 5 m directly north of a bare weighing lysimeter at the USDA‐ARS Conservation and Production Research Laboratory at Bushland, TX. Hourly samples were taken from depth increments of 0 to 2, 2 to 6, 6 to 10, 10 to 30, and 30 to 50 mm. Furthermore, soil cores were taken to 900 mm at 6‐h intervals. Water content was also measured daily at the lysimeter and between the lysimeter and gravimetric sampling plot using a neutron probe to 2.1 m. The submodel accurately predicted that no deep percolation occurred throughout the simulation period. Simulation results agreed well with the measured daily evaporation rates from the lysimeter (r2 = 0.96). Furthermore, the submodel reasonably estimated the soil water content profiles, particularly the status of soil water at the soil‐atmosphere interface. The mean absolute error, which describes the average absolute deviation between measured and simulated soil water contents, was 0.015 m3 m−3. The HYDROLOGY submodel of WEPS shows a potential to accurately simulate soil water dynamics, as needed for wind erosion modeling. The submodel successfully predicts the changes in water content at the soil surface, which relate to the susceptibility of the soil to wind erosion.

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