| There is a pressing need for a practical hydrological model which successfully simulates the soil thermal regime and infiltration on hillslopes in cold regions to assess the effects of management on agricultural sustainability. The preliminary Water Erosion Prediction Project (WEPP) hillslope version 91.5 was evaluated and found to be inadequate for cold regions because the amount and seasonality of runoff were very poorly estimated. A new model, the Cold Region Agricultural Hydrology Model (CRAHM), was developed to simulate agricultural hillslope hydrology in climates where snow and soil frost are important. CRAHM is a continuous two-dimensional simulation model of tillage, residue, crops, precipitation, snowmelt, show drifting, infiltration, runoff, drainage, lateral flow, soil water, and soil temperature on cropped hillslopes. CRAHM is unique among practical hydrologic models in the completeness with which it simulates hydrologic processes and its ability to simulate differences in cropping practices, snow and soil frost states, soil properties, and the soil water regime along the hillslope. CRAHM has fast execution times and simple data needs and is readily implemented on microcomputers. Based on corroboration with 100 plot-years of data from the northwestern United States and southwestern Canada, the soil thermal regime, soil moisture, runoff amount, and runoff peak flow rates all agreed well with those observed. The predicted snowpack followed trends in observed snow amount, although snow drifting was often overestimated or underestimated. The effects of crop rotation and residue management on runoff and soil water content were correctly simulated. The root mean square error between estimated and observed plot runoff was less than the root mean square difference in observed runoff between paired plots. Using CRAHM, divided slope farming in southeastern Washington was predicted to reduce the eroding power of surface runoff by 50% for backslopes and footslopes compared to uniform hillslope management. Model simulations showed that reduced-tillage farming practices which left wheat stubble untilled over the winter increased soil water conservation but decreased seedzone soil temperatures in the spring. |
