Contributions of Anthropogenic Forcings to Evapotranspiration Changes Over 1980-2020 Using GLEAM and CMIP6 Simulations

Anthropogenic impacts on terrestrial evapotranspiration (ET) changes during 1980-2020 were evaluated based on newly released observed-based GLEAM ET and Coupled Model Intercomparison Project Phase 6 (CMIP6) through optional fingerprint method. Global assessments show that anthropogenic forcings dominate the increasing ET trend, other than natural forcing (NAT). On the global scale, anthropogenic forcings explain similar to 84.2% of the observed ET trend, while the signal of natural forcing cannot be detected. Among anthropogenic forcings, greenhouse gases (GHG) are the primary driving factor for ET changes, and GHG-only has already explained similar to 78.8% of the observed ET trend. This study for the first time demonstrates that the GHG signal can be detected in the observed-based ET and can be separable from NAT and aerosol (AER) signals. At the regional scale, CMIP6 simulations work well in North Hemisphere, but are deficient in South Hemisphere. GHG still dominates ET changes in the North Hemisphere, except for Europe, where the influence of AER forcing stands out, and attributable changes to AER is 2.4 times of GHG. Our first quantitative detection and attribution of ET contribute to advance the understanding of anthropogenic activities on hydrological cycle changes.

Automated summary

The study reveals that anthropogenic forcings, especially greenhouse gases, dominate the changes in terrestrial evapotranspiration (ET), explaining a significant portion of the observed trends. While CMIP6 simulations perform well in the Northern Hemisphere, they are lacking in the Southern Hemisphere. The influence of aerosols in Europe stands out, with attributable changes to aerosols being 2.4 times that of greenhouse gases.