Impact of the Agricultural Research Service Watershed Assessment Studies on the Conservation Effects Assessment Project Cropland National Assessment

WATERSHED MODELING AND USDA CONSERVATION POLICY PLANNING The Soil and Water Resources Conservation Act (RCA) of 1977 provides the USDA broad strategic assessment and planning authority for the conservation, protection, and enhancement of soil, water, and related natural resources (USDA NRCS 2011). Through RCA, USDA

• appraises the status and trends of soil, water, and related resources on nonfederal land and assesses their capability to meet present and future demands;

• evaluates current programs, policies, and authorities; and

• develops a national soil and water conservation program to give direction to USDA soil and water conservation activities.

WATERSHED MODELING AND USDA CONSERVATION POLICY PLANNING

The 1985 RCA Appraisal was the first to use a comprehensive model (EPIC; Erosion Productivity Impact Calculator) to estimate the impact of soil erosion on crop productivity (Williams et al. 1984). EPIC is a field-scale model, and thousands of representative fields were modeled across the agricultural regions of the continental United States. The first watershed-based RCA assessment, called the Hydrologic Unit Model for the United States (HUMUS), was undertaken for the 1997 RCA Appraisal (Srinivasan et al. 1998; Arnold et al. 1999). HUMUS provides the necessary technical basis that enables the status of the nation's water resources to be determined at the national scale. The HUMUS framework enables modeling of spatially…