Modeling the Nonlocal Effects of Summer Growing Season Irrigation in the Great Plains

Irrigation practices in the United States have greatly intensified since the early 1930s with Great Plains states like Nebraska leading the country with most acres irrigated. This increase in water application is likely altering the local atmosphere as various studies have confirmed similar changes near other irrigated soils. The most marked local changes include increased low level moisture, decreased temperatures and decreased precipitation which evolve to further affect convective and boundary layer processes. These local changes suggest atmospheric modification much further downstream of irrigated land may be potentially significant given the potential for rapid chaotic perturbation growth, but the degree of this modification is still poorly understood. This study’s purpose is to better understand how increased soil moisture affects convection advancing over irrigated land and the frequency and magnitude of nonlocal weather modification that it causes.

This sensitivity analysis of atmospheric variables begins with multiple soil moisture perturbation variations over the eastern two-thirds of Nebraska using the Advanced Research (ARW) Weather Research and Forecasting Model Version 3.5.1 (WRFV3.5.1). Instead of taking a case study approach to this experiment, the methodology consists of experiments over three summer growing seasons where high precipitation events occur during the first 24 hours in Nebraska over a 96 hour forecast. This allows for the observation of irrigation’s more general, widespread effects on weather downstream in areas as far as the Eastern seaboard. A combination of principle component analysis and empirical orthogonal function analysis is used to produce temporal trends and loading patterns of precipitation to identify how areas of nonlocal weather modification are linked to the increased soil moisture in Nebraska. The use of three summer growing seasons is also expected to provide an understanding into the climate’s contribution to this modification since each year is associated with different base soil moisture values. Using this large dataset over a long temporal scale will allow for more robust results and better insight into nonlocal inadvertent weather modification due to irrigation.