Rarest extreme rainstorms will become even more intense
Rare extreme rainfall events, which occur roughly once every hundred years, will show the greatest increase in magnitude under future climate change. Researchers from Delft University of Technology publish this in Nature Communications. They calculated this based on 25 different climate models and data analysis on the global domain. The magnitude of these very rare rainstorms will increase much more than that of "common" extremes, that occur about once a year. PhD student Gaby Gründemann calculated rainfall extremes in 2071-2100 for four future scenarios, ranging from a world in which population growth and fossil energy use continue to increase, to one that focuses on sustainability and decreasing CO2 emissions. Either way, both the rarest rainfall events and annual rainfall extremes will become more intense in each scenario.
It comes as no surprise that precipitation is increasing due to global warming. But thanks to new analyses, we now know the consequences of various levels of CO2 emissions. Using several climate models from the IPCC reports, Gründemann and her colleagues calculated extreme rainfall around the world for multiple future scenarios. The very rare centennial rainstorms will increase more in severity than the extreme rain that occurs about once a year. "Extreme rainstorms, like the one in Limburg in 2021, will be much more intense by the end of this century. This will have major impacts if we do not take far-reaching measures to combat flooding. Thanks to this research, we now know better where in the world we can expect the increase," Gründemann says.
Each future scenario predicts more extreme rainfall events
In the most favourable scenario, in which we greatly reduce greenhouse gas emissions, rare rainfall events over land will increase by approximately 14%. In the most unfavourable scenario, where emissions will rise even more sharply, precipitation extremes will increase by approximately 38%. Gründemann: "Which scenario we could expect is unknown, as it depends on many factors including the international effort to combat climate change. Cutting CO2 emissions will certainly have an effect. But one thing we know for sure: the increase is creeping. Even at best, floods are expected to increase. Looking further ahead to see how the climate develops, and acting accordingly, is therefore important."
The findings were calculated on the basis of 25 international climate models on which the IPCC reports are also based. Therefore, this study builds on other state-of-the-art research. The researchers noticed that all models predict the same outcomes for precipitation on land: the rarer the extremes, the more their relative increases.
Centennial rainfall (in 2071-2100) increases relatively most around the equator (dark blue) compared to the rainfall in the late 20th century. In a few places over the ocean, precipitation extremes will become slightly less intense.
Especially around the equator
Rainfall will not increase equally across the world. "Africa, for example, will be hit much harder compared to the Netherlands," Gründemann says. Especially around the equator, the extreme rainfall events will become even more extreme. For example, in central and northern Africa, the Amazon and northern Australia. In the Netherlands, the extreme rainstorms will certainly become more intense (12-26%), but not in the same order of magnitude as in Africa (17-90%).