Measuring Environmental Benefits of Conservation Practices: The Conservation Effects Assessment Project (CEAP)-A Model Calibration Approach at the National Level

Abstract

The purpose of the Conservation Effects Assessment Project (CEAP) is to provide peopleinvolved with environmental policy issues an accounting of the environmental benefits obtained fromUnited States Department of Agriculture (USDA) conservation program expenditures. There are twomain components in CEAP: (1) The national assessment and (2) watershed assessment. This paperwill focus on the calibration aspects of modeling component of the national assessment part of theproject. The primary focus of the project is on cropland where most of the conservation practices wereimplemented. Hence field level modeling for CEAP will be conducted by APEX (AgriculturalPolicy/Environmental eXtender). Outputs from the APEX model runs will be input to the watershedscale model Soil and Water Assessment Tool (SWAT) in HUMUS (Hydrologic Unit Modeling for theUnited States) setup to route flow, sediment, and pollutants to the outlet of each watershed indifferent agricultural regions. Environmental benefits at the national scale will be estimated based onthe differences in output between the two scenarios before conservation practices and afterconservation practices. In this modeling approach a calibration is necessary to compensate for theuncertainties in input data. The scale of the study, limits manual calibration. Hence an automatedcalibration procedure is developed to manage the large-scale calibration efforts. The auto-calibrationprocedure automatically adjusts the input parameters in HUMUS-SWAT so that the annual averagestream flow and sediment yield values from HUMUS-SWAT system match to that of SPARROW(SPAtially Referenced Regression On Watershed attributes) model estimates for each 8-digitwatershed.