Effects of Great Plains Irrigation on Regional Climate

Abstract

Irrigation provides a much needed source of water in regions of low precipitation such as the western Great Plains. However, adding water to a region that would otherwise see little natural precipitation has ramifications for the partitioning of radiative and turbulent fluxes, the development of the planetary boundary layer, and the transport of water vapor from the regions of irrigation. The first two effects have the potential to drastically alter the climate of irrigated regions of the Great Plains, while the transport mechanism can alter precipitation processes of regions far downstream of the irrigated areas. These effects are investigated in this thesis through the employment of the Advanced Research (ARW) implementation of the Weather Research and Forecasting Model (WRF) version 3.1.1 using a pair of simulations representing an irrigated and non-irrigated Great Plains. It will be shown that the introduction of irrigation in the Great Plains alters the radiation budget by increasing latent heat flux and cooling the surface temperatures. These effects, in turn, provide additional moisture to the atmosphere and increases the net radiation at the surface, thus increasing moist static energy in the boundary layer and providing downstream convective systems with additional energy and moisture. The increase in atmospheric moisture nearly doubles precipitation accumulations downstream without producing any new precipitation events.