It is well-established that climate change does interfere with the planet’s water cycle, but new studies show we underestimated the impact.
Climate change alters the global atmospheric circulation, which in turn alters precipitation and evaporation in large parts of the world.
For example, streamflow from a river channel is formed by run-off aggregated from the upstream contribution area (or catchment), in turn, providing an essential freshwater resource for sustaining humans and ecosystems
However, new data analyses conducted under the leadership of Prof. Günter Blöschl (TU Wien, Vienna) indicate that previous models systematically underestimate how sensitive water availability reacts to certain changing climate parameters.
Observation of stream flow from 9,505 catchments across the globe shows that climate change can lead to local water crises to an even greater extent than previously expected.
The new study found that in the near future (2021–2050) global streamflow may be lower than predicted by Earth System Models, particularly in Africa, Australia, and North America. The results have now been published in the scientific journal Nature Water.
“In the climatology community, the effects of climate change on the atmosphere are very well understood. However, their local consequences on rivers and the availability of water falls into the field of hydrology,” explains Prof. Günter Blöschl from the Institute of Hydraulic Engineering and Water Resources Management at TU Wien, according to Science Daily.
As Professor Blöschl explains, water availability is related to external parameters such as precipitation or temperature. And locally, around the world, measuring stations do provide information related to various parameters, but global conclusions cannot be drawn from such individual observations.
“How the water balance depends on external parameters varies from place to place; local vegetation also plays a very important role here,” says Günter Blöschl, reports Phys.Org. It is difficult to develop a simple physical model that can be used to calculate these interrelationships at all places in the world with precision.
To address the problem, Blöschl collaborated with colleagues from China, Australia, the USA, and Saudi Arabia to build up and analyze a large database of streamflow observations from all over the world, some going back several decades.
“So we don’t base our analysis on physical models, but on actual measurements,” Günter Blöschl emphasizes. “We look at how much the amount of available water changed in the past when external conditions change. In this way, we can find out how sensitively changes in climate parameters are related to a change in local water availability. And this allows us to make predictions for a future, warmer climate.”
As it turns out, the connection between precipitation and the amount of water in the rivers is much more sensitive than was previously thought — and thus much more sensitive than is assumed in the models currently used to predict climate change.
Forecasting models of the effects of climate change on water supply should therefore be fundamentally revised. “Up to now, runoff measurements have usually not been included at all in the models, such as those currently reported by the IPCC,” says Blöschl. “With the series of measurements now available, it should now be possible to adjust the physical prediction models accordingly.”
