Agricultural Best Management Practice Sensitivity to Changing Air Temperature and Precipitation

Abstract.Agricultural best management practices (BMPs) reduce nonpoint-source pollution from cropland. Goals for BMP adoption and expected pollutant load reductions are often specified in water quality management plans to protect and restore waterbodies; however, estimates of the needed load reductions and pollutant removal performance of BMPs are generally based on historic climate. Increasing air temperatures and changes in precipitation patterns and intensity are anticipated throughout the U.S. over the 21st century. The effects of such changes on agricultural pollutant loads have been addressed by several studies, but how these changes will affect the performance of widely promoted BMPs has received limited attention. We used the Soil and Water Assessment Tool (SWAT) to investigate potential changes in the effectiveness of conservation tillage, no-till, vegetated filter strips, grassed waterways, nutrient management, winter cover crops, and drainage water management practices under potential future temperature and precipitation patterns. We simulated two agricultural watersheds in the Minnesota Corn Belt and the Georgia Coastal Plain with different hydroclimatic settings under recent conditions (1950-2005) and multiple potential future mid-century (2030-2059) and late-century (2070-2099) climate scenarios. Results suggest future increases in agricultural source loads of sediment, nitrogen, and phosphorous. Most BMPs continue to reduce loads, but removal efficiencies generally decline due to more intense runoff events, biological responses to changes in soil moisture and temperature, and exacerbated upland loading. The coupled effects of higher upland loading and reduced BMP efficiencies suggest that wider adoption, resizing, and/or combining practices may be needed in the future to meet water quality goals for agricultural lands. Keywords: Agricultural management, Best management practices, Climate change, Conservation tillage, Cover crops, Drainage water management, Hydrologic and water quality modeling, Nutrient management, Pollutant removal efficiency, Soil conservation, Vegetated buffer