A process-based hydrology submodel dynamically linked to the plant component of the simulation of production and utilization on rangelands SPUR model

Due to the great diversity and complex interactions of vegetation, soils, and climate on rangelands, process-based models designed to evaluate rangeland hydrology must include sophisticated plant and animal components that simulate changes in vegetation over space and through time. An infiltration-based submodel similar to that used in WEPP (Stone et al. (1995) USDA-Agri. Res. Service, NSERL Report No. 10, Chap. 4) was dynamically linked to the SPUR2.4 rangeland ecosystem model (Foy et al., Ecol. Model. 118 (1999) 149) to provide the framework for future model enhancement and investigation of the impacts of management on the rangeland ecosystem. Model description and documentation of model modifications are presented for SPUR 2000. A sensitivity analysis and initial test of SPUR 2000 were performed using rainfall simulation plot and micro-watershed data from Idaho sagebrush rangeland. The sensitivity analysis showed improved sensitivity of runoff and erosion to various vegetation parameters. The long-term simulations demonstrated good representation of soil water content, peak standing crop, and evapotranspiration. SPUR 2000 did a better job of predicting individual thunderstorm runoff events, and estimated 15-year runoff within 12% compared to SPUR2.4, which grossly overestimated runoff. Neither model accurately predicted sediment loss, but predicted values did demonstrate the relatively small amount of erosion that occurs from these rangelands. Neither model could reasonably estimate the snow-driven runoff that dominates these types of western rangelands. Additional research needs to explore the degree of influence that vegetation has on infiltration and runoff and how it varies for different plant communities. Development of specific Ke estimation equations based on this information will strengthen the vegetation–hydrology linkage within the model.