Sustained decline in the trend of global terrestrial evapotranspiration since year 2000

Evapotranspiration (ET) is a key element of the surface water and energy balances in the earth system. Accurate quantification of ET is therefore crucial for sustainable water resource management, improved understanding of the hydrological cycle and its connections with the carbon cycle and Earth's climate1, 2. Here we propose an improved complementary relationship (CR) formulation to estimate global terrestrial ET more accurately by resolving the partitioning of incoming energy between latent and sensible heat. The estimated global terrestrial ET over 1979-2017 showed an increasing trend before the year 2000 while the trend declined afterwards. Such decline was largely driven by soil water limitation, associated with a large global reduction in soil moisture that occurred, and is still occurring, especially in most parts of Africa, Australia and Europe. The continuing decline in soil moisture over a long time indicates that increased limitations of water supply to support ET are due to climate change rather than natural meteorological oscillations. Furthermore, decreased energy dissipation as ET would result in accelerated warming on the land surface3, and thus enhancing the depletion of soil moisture - a positive climate change feedback loop.