Climate Change Impacts on Runoff, Sediment, and Nutrient Loads in an Agricultural Watershedin the Lower Mississippi River Basin

Abstract. Projected climate change can impact various aspects of agricultural systems, including the nutrient and sediment loads exported from agricultural fields. This study evaluated the potential changes in runoff, sediment, nitrogen, and phosphorus loads using projected climate estimates from 2041-2070 in the Beasley Lake watershed in Mississippi, USA, using the Annualized Agricultural Non-Point Source (AnnAGNPS) pollution watershed model. For baseline conditions and model inputs an earlier validated simulation of the watershed was used with an event-based NSE of 0.81 for runoff and 0.54 for sediment without calibration. Fifteen global climate models (GCMs) for the climate change scenario RCP8.5 in Western Mississippi were used. Daily precipitation and air temperature were generated with the weather generator SYNTOR. Daily climate data derived from all 15 GCMS were used in AnnAGNPS simulations to generate ensemble projected loads, and climate data from four GCMs were used in simulations to assess the effectiveness of five different conservation practices for reducing projected loads. Predicted median annual-average pollutant loads increased by 9% to 12% with ensemble projected climate change. However, no-tillage and cover crop conservation practices were predicted to reduce pollutant loads from 20% to 75% below historical levels despite the impacts of climate change. This study suggests that greater implementation of conservation practices can be effective at mitigating water quality degradation associated with projected climate change.