Remote detection of water management impacts on evapotranspiration in the Colorado River Basin

The complexity involved in accurate estimation and numerical simulation of regional evapotranspiration (ET) can lead to inconsistency among techniques, usually attributed to methodological deficiencies. Here we hypothesize instead that discrepancies in ET estimates should be expected in some cases and can be applied to measure the effect of anthropogenic influences in developed river basins. We compare an ensemble of corrected ET estimates from land surface models with Gravity Recovery and Climate Experiment and Moderate Resolution Imaging Spectroradiometer satellite-based estimates in the intensively managed Colorado River Basin to contrast the roles of natural variability and human impacts. Satellite-based approaches yield larger annual amplitudes in ET estimates than land surface model simulations, primarily during the growing season. We find a total satellite-based ET flux of 142 +/- 7MAF yr(-1) (175 +/- 8.63 km(3) yr(-1)), with 38% due to anthropogenic influences during summer months. We evaluate our estimates by comparison with reservoir storage and usage allotment components of the basin water management budget.