Simulated changes in precipitation intensity due to large-scale cropland irrigation in the Great Plains

Abstract:

The effects of large-scale cropland irrigation on precipitation patterns have been studied extensively over the last several years, but most studies have focused on monthly or seasonal timescales. Since irrigation impacts on precipitation may vary widely on shorter timescales with changing synoptic and mesoscale conditions, we present a modeling analysis of the daily and sub-daily impacts of irrigation on precipitation using the Weather Research and Forecasting (WRF) regional climate model. In particular, we focus on changes in precipitation over and downwind of the US Great Plains, where irrigation has experienced rapid development over the last sixty years. When an irrigation scheme is implemented in the model, preliminary results of simulations for one growing season suggest that precipitation intensity is more likely to be enhanced downwind of, rather than over, the irrigated areas. In addition, the proportion of precipitation events with moderate and heavy precipitation seems to increase downwind of irrigated areas. We discuss other changes in the precipitation distribution (e.g., frequency, duration, and total precipitation) and in precipitation extremes (for both no-rain days and heavy precipitation) both in and downwind of irrigated areas. We also explain certain atmospheric and surface conditions that create a more favorable environment for potential irrigation enhancement of precipitation. Finally, we show preliminary results from a precipitation recycling model to better attribute the irrigation-induced changes in precipitation to either moisture enhancement or stability changes in the affected regions.