First long-term, direct measurements of evapotranspiration and surface water balance in the Nebraska SandHills

The Nebraska SandHills is a vast grassland ecoregion that also serves as the main recharge zone for the High Plains (Ogallala) aquifer. Despite the national importance of this region in supplying irrigation water and supporting the US cattle industry, there have, until now, been no long-term, direct measurements of the components of the surface water balance. We have addressed this issue by installing energy balance/Bowen ratio (EBBR) flux towers in three key ecosystems. We report here the results of 7 years of measurements and interpret them in terms of annual weather variability. Additionally, these data have allowed us to make first-order estimates of the recharge rate to the aquifer. We found that the three ecosystems behave in very different ways, and that, in a first-order estimate, the region provides approximately 115 ± 20 mm year−1 of recharge to the aquifer over the 2003–2009 period.