Southern Hemisphere dominates recent decline in global water availability

Global land water underpins livelihoods, socioeconomic development, and ecosystems. It remains unclear how water availability has changed in recent decades. Using an ensemble of observations, we quantified global land water availability over the past two decades. We show that the Southern Hemisphere has dominated the declining trend in global water availability from 2001 to 2020. The significant decrease occurs mainly in South America, southwestern Africa, and northwestern Australia. In the Northern Hemisphere, the complex regional increasing and decreasing trends cancel each other, resulting in a negligible hemispheric trend. The variability and trend in water availability in the Southern Hemisphere are largely driven by precipitation associated with climate modes, particularly the El Niño-Southern Oscillation. This study highlights their dominant role in controlling global water availability. How has climate change affected the availability of land water over the recent past? Zhang et al . calculate global land water availability over the last two decades and found an overall decline that has been dominated by a negative trend in the Southern Hemisphere, whereas a mixture of positive and negative regional trends in the Northern Hemisphere have led to no significant change there (see the Perspective by Blöschl and Chaffe). El Niño is the most important climate mode affecting water availability in the Southern Hemisphere. —H. Jesse Smith Large-scale atmospheric climate modes dominate the recent decline in global water availability.