0608 GMT September 27, 2020
Water is the lifeblood of ecosystems and one of the most important natural resources for human beings. But available terrestrial water — that is, the amount of water left from precipitation after evaporation—is not just distributed unevenly across the planet, it is also changing over time. Observations show that the available volume of water has been falling in some regions of the world for a few decades. One example is southern Europe, where aridity is increasing. But in other areas water supplies are trending upwards, phys.org reported.
The causes of this change in water availability pose an urgent question — and not only for those countries suffering from acute water shortages. Is anthropogenic climate change to blame, or is it simply random fluctuations in the climate system? To date, there has been no definitive answer at a global level.
It is scientifically indisputable that increased atmospheric concentrations of CO2 influence the complex global water cycle in various ways. But until now it has been impossible to prove a direct effect of global warming on available terrestrial water resources over recent decades. The historical observation series, sometimes too brief and qualitatively inadequate, did not enable exclusion of natural climate variability as the cause of the changes observed.
Now, an international research team led by Sonia Seneviratne, ETH Professor of Land-Climate Dynamics, has proved this. As the scientists report in the current edition of Nature Geoscience, they reconstructed worldwide water availability in the driest month of years between 1902 and 2014 using climate models and new observations-based data.
In order to determine how water availability changed over time, the researchers compared the reconstructed water resources of the years 1985 to 2014 with those of the first half of the 20th century. In this way they mapped out a global pattern of changes in available water over the past three decades. In this pattern, the researchers found the fingerprint of climate change.