Global Water Scarcity Risk Elevated by Considering Rain’s Upwind Origins

A new study by researchers at Stockholm University presents an alternative approach to assessing global water scarcity risks, suggesting these risks may be higher than previously thought when considering the environmental conditions and governance of areas where rain originates. The study, published in Nature Water, highlights the importance of upwind moisture sources—areas where water evaporates and travels through the atmosphere before falling as rain— in evaluating water supply risks.

Traditionally, water scarcity assessments focus on water sources such as aquifers, lakes, and rivers, where rainwater is stored after falling to the earth’s surface. However, the study emphasizes the need to consider the conditions of the “precipitationshed”—the upwind areas contributing moisture to a region’s rainfall. According to Fernando Jaramillo, associate professor in physical geography at Stockholm University, these upwind factors are often overlooked in current water availability evaluations.

The research analyzed 379 hydrological basins globally, finding that risks to water security increase significantly when the upwind sources of moisture are taken into account. The study indicates that 32,900 km³ of global water demand per year faces a high risk, a nearly 50% increase compared to the 20,500 km³/year identified using traditional methods focusing on upstream factors.

The study also reveals how changes in land use, such as deforestation or agricultural expansion in upwind areas, can reduce moisture levels available for rainfall downwind, impacting water security in regions far from the initial source of evaporation. For instance, in tropical South America, the Amazon basin and the Andes region depend on each other for moisture, highlighting the interconnectedness of these areas’ water supplies.

Political and environmental management practices in upwind areas can significantly influence water availability downstream. For example, the Congo River basin relies on moisture from neighboring countries, where inadequate environmental governance could exacerbate water scarcity risks due to deforestation and other land-use changes.

The researchers advocate for a broader perspective on water governance, incorporating an understanding of upwind moisture sources and their influence on regional and transboundary water security. They call for international cooperation to address these interconnected risks, emphasizing the need to include atmospheric water flows in transboundary water management strategies.