Evapotranspiration frequently increases during droughts

Changes in evapotranspiration (ET) substantially affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce the moisture supply necessary for ET. These competing factors limit straightforward prediction of even the sign of ET anomalies during droughts.  Drought-driven increases in evapotranspiration (ET+) are of particular concern because they quickly deplete water resources, causing flash droughts and acute stress on ecosystems. Here, we used GRACE/GRACE-FO and a water balance approach to show that ET+ is globally widespread, occurring in 44.4% of drought months. The sign of ET’s drought response depends most on the magnitude of precipitation and of total water storage anomalies, rather than its location. CMIP6 Earth system models underestimate the ET+ probability by nearly half, and more so in drier regions, primarily due to missing representations of soil structure effects on soil evaporation, and incorrectly parametrized plant and soil traits. These processes should be prioritized to reduce model uncertainties in the water-energy-food nexus.