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Number of people exposed to extreme drought could double by end of 21st century

International climate study predicts total mass of land water for the first time

International research led by Michigan State University and in collaboration with the Vrije Universiteit Brussel has led to the first simulations of the impact of climate change on the total mass of water on land. Co-author and VUB climate scientist Prof Wim Thiery: “By the end of the 21st century, the global land area affected by extreme drought could more than double – from 3% in the period 1976-2005 to 7%. In this moderately pessimistic scenario, almost 500 million more people will be affected by extreme drought.” The study was published in the renowned journal Nature Climate Change.

Until now, no study had examined how future climate change could affect the total storage of land water worldwide. There is a reason for this. Projections of drought are very difficult because there are many ways to define drought: lack of precipitation, amount of soil moisture, groundwater level, river low flows, etc. Depending on the focus and the method, the results of drought predictions can vary considerably. That is why a new satellite was launched a few years ago. The GRACE satellite can measure changes in the total mass of water by mapping changes in the earth’s gravitational field. The total mass of water, or terrestrial water storage (TWS), is the accumulation of water in snow and ice, rivers, lakes and reservoirs, swamps, soil and groundwater – all critical components of the world’s water supply. TWS modulates the water flow within the hydrological cycle and can therefore determine the availability of water and the prevention of drought.

Thiery explains the new method: “The difference with previous studies is that, just like the GRACE satellite, we looked at the total amount of water in our computer models, i.e. snow, soil moisture, groundwater, lakes, etc., all at the same time. It is also the first time that scientists have used hydrological models to investigate how the TWS could evolve in the future. The results show a large reduction in natural land water storage in two-thirds of the world under a medium emissions scenario, especially in the southern hemisphere. This reduction is largely driven by climate change.”

This reduction in TWS will increase the likelihood of extreme droughts, potentially more than doubling the number of people exposed to exceptional drought in this scenario by the end of this century. “More and more people will suffer from extreme droughts as long as global warming continues and water management is maintained in its current state,” Thiery says. “We predict that this increase in water scarcity will affect food security, increase migration and fuel conflict.”

“Our findings show that we need to limit climate change in order to avoid negative impacts on global water supplies,” adds Prof Yadu Pokhrel of Michigan State University, hydrologist and lead author of the study. “We must also work towards better water management and adapt to dwindling water resources in order to avoid the potentially catastrophic consequences of water shortages.”

The study is based on a set of 27 global hydrological model simulations over 125 years, some of which were generated by VUB, and was carried out as part of a global research project called the Inter-Sectoral Impact Model Intercomparison Project.

Nature Climate Change publication: https://www.nature.com/articles/s41558-020-00972-w