Government agencies have emphasized the need to provide sound, science-based technology to model and predict the benefits of conservation technical assistance, rangeland hydrology and erosion for National Resource Inventories, and for Ecological Site development.  The need and ability to monitor and assess rangeland conditions is an important function for land managers and conservationists across the western United States.  On rangelands, it is imperative that hydrologic components are linked with erosion dynamics and ecological functions in the plant community. SWRC is developing a new Rangeland Hydrology and Erosion Model (RHEM) for inclusion as a module in a comprehensive agency-wide erosion prediction and conservation planning technology for water and wind erosion.  Central to this effort is a process-based hydrologic and soil erosion model, development of algorithms for parameterizing the model from system state assessments such as the National Resource Inventory or Ecological Site Descriptions, and coupling an ecological/plant productivity component.  The end product will be a multi-tiered hydrologic and soil erosion prediction technology based on process-based hydrologic and erosion science.  First, a model will be developed for making estimates of runoff, soil erosion, and sediment yield rates as a function of soil, slope, and plant community for single storms.  Data for parameterizing, testing and validating the model will come primarily from past experiments such as The Interagency Rangeland Water Erosion Team experiments of 1990-93 which included 156 plots at 26 sites in 10 western states of the US, the WEPP rangeland field experiments of 1988-99 which included 102 plots at 20 sites in 9 western states, and long-term small watershed data from Aaizona.  The model will be expanded to include annualized runoff, soil erosion, and sediment yield rates.  This phase will involve the use of weather generators, plant models, and evapotranspiration routines.