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.