20 February 2019

Publication Geophyscial Research Letters

Global warming of two degrees will make extreme droughts more common

Global warming of 2°C will cause more extreme hydrological situations on earth. This is the conclusion of researchers from Utrecht University and the Royal Netherlands Meteorological Institute (KNMI), published this week in the journal Geophyscial Research Letters. The researchers demonstrate that extreme drought such as in 2018 will become more common if the global temperature rises by two degrees as a result of climate change. ​

Laag water aan de Waalkade. Foto: Tim Hahn
The Waal in Nijmegen reached a historical low in October 2018. Picture: Tim Hahn

The summer of 2018 will be remembered as an extremely dry summer. Grass was sooner yellow than green, farmers were only permitted to spray their fields in moderation and crops were a lot smaller than usual, meaning the produce could not be sold. Dutch newspaper Algemeen Dagblad reported that farmers are already concerned about the summer of 2019. Winter is now coming to an end, we have seen plenty of downpours and on the face of it, little evidence of last year’s drought remains. However, our water table is unfortunately still to recover and with a view to global warming, droughts such as that of 2018 are set to return with increasing frequency and intensity. 

2,000 years of climate studies

Researchers from Utrecht University worked together with colleagues from the KNMI to compare various scenarios, in which the current climate is compared with that in a world that is two degrees warmer. Using climate models from the KNMI and hydrological simulations developed by Utrecht University, the researchers were able to view and analyse 2,000 years of potential weather conditions.

“What makes these scenarios unique is that they help us to better forecast how the current level of global warming will impact extreme years such as 2018, or even worse”, says Niko Wanders, hydrologist at Utrecht University specialising in hydrological extremes. “We normally examine the measurements from recent years. These new simulations facilitate vastly improved forecasts, meaning we gain better insight into what extreme drought really is. Now and in the future”.

Grafiek: de kans (herhalingstijd) van een extreme droogte in de Rijn
The risk of extreme drought in the Rhine. The longer the interval, the lower the frequency. Crosses indicate measurements conducted by Lobith, black = expectation with the current climate and red = forecasted situation in the case of global warming of 2°C

Examining extreme drought and a rising sea level

The researchers concluded that a two degree rise in global temperature would make the European land surface additionally vulnerable to drought. Not only in the Netherlands, but also in countries where the Rhine and Maas rise. “If less water enters the Netherlands via rivers, while sea level rises, we will need all of that river water to prevent salinization of the groundwater”, adds hydrologist and co-author prof. Marc Bierkens from Utrecht University. “Saltwater intrusion is already a major problem, which is only exacerbated in periods of drought”.

Adjustments

Wanders says that we need to take a sustainable approach to water management. After all, we cannot influence the amount of water entering our country. In the case of global warming of two degrees, there is simply less water available, so it is essential that we make proper preparations. By reducing demand for water, for example, or ensuring that our water management is flexible. These measures should ideally be taken in the short term, as this warmer climate will be a reality in just 30 years if the world continues to produce greenhouse gasses at the current rate.