PNNL

Abstract

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 quantify global land water availability over the last two decades. We show that the Southern Hemisphere has dominated the declining trend in global water availability in 2001-2020. The significant decrease mainly occurs 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 highlights their dominant role in controlling global water availability.