Estimating long-term changes in actual evapotranspiration and water storage using a one-parameter model

•We use GRACE data to parameterize a simple water balance model.•We find evapotranspiration has increased in the Missouri River Basin over 80 y.•Water storage has also increased despite no trend in the “change in storage”.

SummaryEstimations of long-term regional trends in evapotranspiration (E) and water storage are key to our understanding of hydrology in a changing environment. Yet they are difficult to make due to the lack of long-term measurements of these quantities. Here we use a simple one-parameter model in conjunction with Gravity Recovery and Climate Experiment (GRACE) data to estimate long-term E and storage trends in the Missouri River Basin. We find that E has increased in the river basin over the period 1929-2012, consistent with other studies that have suggested increases in E with a warming climate. The increase in E appears to be driven by an increase in precipitation and water storage because potential E has not changed substantially. The simplicity of the method and its minimal data requirements provide a transparent approach to assessing long-term changes in hydrological fluxes and storages, and may be applicable to regions where meteorological and hydrological data are scarce.