Large-scale water cycle perturbation due to irrigation in the US High Plains

This study investigates the hydrologic and climatic impacts of large-scale irrigation in the US High Plains to elucidate the influence of human activities on the natural water cycle. The US High Plains (between 104°W-96°W and 32°N-44°N) is one of the major agricultural regions in the world covering parts of eight states from southern Dakota to northwestern Texas with a surface area of 450,000 km2. Herein, it is hypothesized that the extensive irrigation development throughout the region during 1940-1980 has resulted in three potential impacts on regional hydrology and climate. 1) depletion of streamflow in the High Plains, 2) enhancement of warm-season precipitation downwind of the High Plains, and 3) increases in downwind groundwater storage and streamflow, over the period of irrigation development (1940-1980). Each of these hypothesis were tested using advanced statistical methods such as Mann-Kendall and Pettitt test and as many observations as possible. The results of this research demonstrated that large-scale irrigation in the High Plains significantly altered the hydrologic and climatic patterns over and downwind of the study area by causing; 1) depletion of both annual and summer streamflow in the High Plains, 2) increase of July precipitation over the Midwest, and 3) increased groundwater storage and streamflow in the Midwest during August and September. Additionally, this study establishes the facts that human-induced modifications on the hydrological cycle are drastic and their effects are far-reaching, and, also, attribution of hydrologic changes to correct causes is of crucial importance for better sustainability of ecosystems and future climate change predictions.