Water-budget based Evapotranspiration product captures natural and human-caused variability

Abstract

Evapotranspiration (ET) is one of the most important yet highly uncertain components of the water cycle. Available modelled ET products do not necessarily agree with each other at various spatiotemporal scales, either due to limitations on input data and/or due to model assumptions and simplifications. Therefore, using water budget equation to estimate ET has gained attention. However, a large number of water-budget combinations with large uncertainties are available that increases ambiguity in choosing the best ET estimate. Here, the Kalman filter is employed for ingesting 96 water-budget based ET estimates and produce a global ET product with uncertainty < 2 mm, and it captures the general spatiotemporal pattern of ET and the inter-annual variability over all continents. Since the water budget includes storage change due to human interventions, our ET estimates are superior over regions with strong irrigation signal, such as the Ganges basin. We verify our claim by using a modified variable infiltration capacity model that simulates irrigation activities as well. Our ET estimates have a global mean positive trend of 0.18 ± 0.02 mm/year with larger regional variations that are discussed.