Interesting new paper by Mekonnen and Hoekstra. Here’s the abstract:
Freshwater scarcity is increasingly perceived as a global systemic risk. Previous global water scarcity assessments, measuring water scarcity annually, have underestimated experienced water scarcity by failing to capture the seasonal fluctuations in water consumption and availability. We assess blue water scarcity globally at a high spatial resolution on a monthly basis. We find that two-thirds of the global population (4.0 billion people) live under conditions of severe water scarcity at least 1 month of the year. Nearly half of those people live in India and China. Half a billion people in the world face severe water scarcity all year round. Putting caps to water consumption by river basin, increasing water-use efficiencies, and better sharing of the limited freshwater resources will be key in reducing the threat posed by water scarcity on biodiversity and human welfare.
A major change from past estimates is the use of higher temporal resolution (monthly vs annual) indications of water scarcity. A couple of other issues are the spatial scale and the lack of environmental flow requirements. The presented numbers are pretty concerning — the monthly approach suggests scarcity is about 1.3-2 times more prevalent than previous estimates.
The supplementary materials are also worth reading and include an additional set of figures and a table summarizing some of the earlier estimates.