Identifying Cause of Declining Flows in the Republican River

Abstract

The Republican River, shared by three states, Colorado, Nebraska, and Kansas, has yielded depleted streamflow at the Nebraska-Kansas border for about 20 years when compared to values preceding 1970. Based on model results estimating the average annual water balance of the basin, it is concluded that the observed decline in runoff cannot be explained by changes in climatic variables over the area; rather, it is the result of the combined effects of the following human activities: crop irrigation, change in vegetative cover, water conservation practices, and construction of reservoirs and artificial ponds in the basin. These human-induced changes have one property in common: they all increase the amount of water being evaporated over the basin, thereby reducing the amount of water available to runoff.