Traditionally, global water supply assessments focus on the rain falling directly on the earth's surface, which is then stored in aquifers, lakes, and rivers. However, a recent study published in *Nature Water* emphasizes the importance of upwind areas-regions where moisture evaporates before traveling through the atmosphere and falling as rain-in evaluating water security risks.
"Water supply really originates beforehand, with moisture evaporated from land or in the ocean traveling in the atmosphere before falling as rain. This upwind moisture is commonly overlooked when assessing water availability," says Fernando Jaramillo, associate professor in physical geography at Stockholm University and responsible for the study.
When examining 379 hydrological basins worldwide, the study found that risks to water security are significantly higher when the origin of the moisture, or precipitationshed, is taken into account. "With this approach, we see that 32,900 km3/year of water requirements worldwide face very high risk, a near 50 percent increase, compared to the 20,500 km3/year resulting from the more traditional upstream focus," says Jose Posada, former doctoral student at Stockholm University and main author of the study.
The research underscores the impact of political control and land use changes in upwind areas on downwind water availability. For instance, deforestation and agricultural expansion in upwind regions can reduce the moisture available for downwind precipitation, thereby increasing water scarcity risks.
The study also highlights the significant risks faced by inland countries, where rain largely depends on moisture evaporated in neighboring regions.
"For coastal countries such as the Philippines, most of the rain comes from the sea, which means that land-use changes pose very little risk to water security. Rainfall in inland countries such as Niger, on the other hand, comes mainly from moisture that evaporates in neighboring countries such as Nigeria and Ghana. This puts many land-locked countries at high risk regarding how water security is affected by changes in land use," says Fernando Jaramillo.
Political and environmental governance in upwind regions is crucial for ensuring water security in downwind areas. "The Congo River basin, heavily reliant on moisture from neighboring countries with low environmental performance and governance according to global indicators, faces considerable risks due to potential deforestation and unregulated land use changes in neighboring areas," says Lan Wang-Erlandsson, researcher at the Stockholm Resilience Centre at Stockholm University and co-author of the study.
The study calls for an upwind perspective in environmental regulation and emphasizes the interconnected nature of water resources. "It is not possible to ignore the interdependence between countries. In the end, all water is connected, so we should not only mind how we manage our water resources within a region or country but also how our neighboring countries do," says Lan Wang-Erlandsson.
Related Links
Bolin Centre for Climate Research
Water News - Science, Technology and Politics
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