Hydrological Responses to Warming: Insights From Centennial‐Scale Terrestrial Evapotranspiration Estimates

Abstract Quantifying changes in global terrestrial evapotranspiration (ET) is essential for understanding how the hydrological cycle responds to climate change. Most current ET estimates are limited to the satellite observation era, starting in the 1980s, leaving the dynamics of global ET over longer time scales, such as the past century, largely unknown. Based on thoroughly validated centennial‐scale global ET rates, estimated by the complementary relationship method, here we show that global ET significantly increased with a trend of 0.08 ± 0.011 mm yr −2 ( p < 0.001) during 1901–2014, equivalent to an accumulated relative increase of 1.8 ± 0.2%. This pronounced increase provides robust evidence of the intensification of the hydrological cycle on a centennial scale. The increase in global ET has mainly occurred in the most recent five decades, as the trend during 1966–2014 is five times as large as that during 1901–1965. From 1901 to 2014, the scaling rate of global ET to temperature ( η ae ) is 1.3 ± 0.3% °C −1 . Notably, η ae remains nearly constant across different timescales, despite an accelerated warming and rising atmospheric CO 2 concentrations in the recent past. Similar findings of stable η ae values can also be observed in the state‐of‐the‐art land surface models, despite being parameterized in more complex ways. This timescale invariance property may enable the application of a constant η ae value to facilitate predictions of future global ET changes based solely on temperature projections. These findings have relevance for global‐scale water resources management under the ongoing climate change.