The risk of global water shortages is greater than previously thought, new research shows

The common idea of global water supply is rain falling on the earth's surface, stored in aquifers, lakes, and rivers. This idea is usually used to assess water security and risk of scarcity. But a new study, published in Nature Water, shows how the assessment of the stability of the global water supply is dependent on factors much earlier in the system, which means global risk to water supply changes if you also consider the source of the rain.

“Water supply really originates beforehand, with moisture evaporated from land or in the ocean travelling 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 a lake or river is shared between different countries or authorities, assessments and regulations mainly apply an upstream perspective of what is occurring within the specific water body. In other words in the water itself. An upwind perspective also takes the area where evaporated water is transported from before ending up as rain. The area is known as a precipitationshed and can cover large areas of the earth’s surface.

The study examined 379 hydrological basins worldwide, revealing that risks to water security are significantly higher when considering the upwind origin of water.

“With this approach, we see that 32,900 km3/year of water requirements worldwide face very high risk, a near 50 per cent increase, compared to the 20,500 km3/year resulting from the more traditional upstream focus,“ says José Posada, former doctoral student at Stockholm University and main author of the study.

Dependent on many different systems

Precipitation on Earth depends on many different currents, both in the atmosphere, on land and in the ocean, making the new method of risk calculation more complete. In meteorology, a wind direction is the direction the wind is coming from. The term 'upwind' is in the direction of the source of the wind and 'downwind' is in the direction away from the source. The study highlights the importance of adding these concepts in risk assessments, as a complement to the water currents upstream and downstream.

“For instance, in tropical South America, most of the Amazon basin is downstream of the Andes mountain range, whereas large areas of the Andes are in themselves downwind of the Amazon rainforest and depending on it, which makes these two regions dependent on each other for water supply,” says Fernando Jaramillo.

Political control

Since a large amount of water is evaporated from plants, changes in land use can affect downwind water availability. If deforestation and agricultural development are predominant in the neighboring countries, the amount of moisture that vegetation provides upwind may decrease reducing rainfall and increasing risk to water security.

"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 makes many countries in land locked countries high-risk countries when it comes to how water security is affected by changes in land use," says Fernando Jaramillo.

In other words, political factors such as environmental management and regulations in areas from which the moisture first evaporates can affect water safety in completely different areas. Unregulated deforestation or land use changes in adjacent areas can entail serious risks, but are difficult to control.

“For instance, the Congo River basin, heavily reliant on moisture from neighboring countries with low environmental performance and governance according to global indicators, faces severe risks due to potential deforestation and unregulated land use changes in neighboring areas,“ says Lan Wang-Erlandsson, Centre researcher and co-author of the study.

An upwind perspective

The study reveals why accounting for lack of governability and environmental performance in countries upwind is critical for the water supply of other countries. It stresses the codependence between upstream/downwind and downstream/upwind countries.

"It is not possible to ignore the interdependence between countries when it comes to the water issue in a river basin or catchment area. 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 we and our neighbors can affect the overall water supply,” says Lan Wang-Erlandsson.

And access to fresh water is an issue that as a result of this creates tensions between regions.

"We hope that the findings of this study can help identify where and to whom cooperation strategies and efforts can be directed to mitigate the causes of water-related tensions, including atmospheric water flows in transboundary decision-making and water governance frameworks. We stress the need for international cooperation to effectively manage upwind moisture sources,“ concludes Fernando Jaramillo.