A new study finds that the Southern Hemisphere is responsible for over 95% of the recent drop in global water availability, which is partly driven by large-scale atmospheric climate modes. Climate change and rising human water consumption have caused variations in the availability of land water worldwide. Even though water is an essential resource that supports ecosystems, socioeconomic growth, and livelihoods globally, it is yet unknown how and why water availability has altered recently on a global scale.
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To determine the global land water availability for the past 20 years, Yongqiang Zhang and colleagues use a variety of data, such as streamflow observations of major river basins worldwide, terrestrial precipitation data, and satellite measurements of evaporation and water storage.
The results showed a decrease in the availability of land water worldwide between 2001 and 2020. However, variability and a negative trend in water availability in the Southern Hemisphere accounted for more than 95% of the global variance in land water availability, accounting for only 26% of the global land surface.
Across the Southern Hemisphere, water availability decreased significantly over the study period—around 3.55 millimeters each year over the last 20 years. In contrast, a complex mix of positive and negative trends in various Northern Hemisphere locations have mostly canceled each other out, resulting in a small change in land water availability during the same time.
According to Zhang et al., the variability and trend in Southern Hemisphere water availability are mostly influenced by changes in large-scale atmospheric climate patterns, particularly the El Nio-Southern Oscillation. Günter Blöschi and Pedro Chaffe explore the topic in greater depth in a related Perspective.
Zhang, Y., et al. (2023) Southern Hemisphere dominates recent decline in global water availability. Science. doi:10.1126/science.adh0716