Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8895053 | Journal of Hydrology | 2018 | 36 Pages |
Abstract
Trends in monthly evapotranspiration (ET) rates across Nebraska, the most intensely irrigated state within the US, were calculated by the calibration-free version of the nonlinear complementary relationship of evaporation over the 1979-2015 period utilizing North American Regional Reanalysis (NARR) net radiation, 10-m wind velocity, as well as Parameter Regression Independent Slope Model (PRISM) air- and dew-point temperature data. State-averaged modeled ET rates rose by 5.5â¯mmâ¯decadeâ1 due to the presence of wide-spread large-scale irrigation projects in accordance with a 2.4â¯mm decadeâ1 increase in PRISM precipitation (P) and a simultaneous â2.8â¯mmâ¯decadeâ1 drop in United States Geological Survey's state-averaged annual streamflow rates, raising the state-wide ET to P ratio from 0.89 to 0.91 over the modeled time-period. ET rates over irrigated crops increased by 7â¯mm decadeâ1 despite a â4.4â¯mmâ¯decadeâ1 drop in precipitation rates. A similar increase in ET rates (6â¯mm decadeâ1) required 8.1â¯mm decadeâ1 increase in precipitation rates across the non-irrigated Sand Hills of Nebraska. Published NARR ET rates are unable to pick up this unusual regional trend. Since an increase in precipitation rates should normally decrease the ET ratio, as predicted by the Budyko curve, this study yields evidence on how dramatically sustained large-scale irrigation can alter the regional hydrologic cycle not only through a) trivially depleting streamflow rates and/or lowering groundwater table levels; b) suppressing precipitation locally (while enhancing it a long distance downwind), but also; c) reversing the trajectory of the regional ET ratio under generally increasing trends of precipitation.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
Jozsef Szilagyi,