Clear link between global warming and heavy rainfall and flooding for the first time

The assumption that there is an increase in heavy rainfall events and thus more frequent small-scale flooding due to the climate crisis has now been proven in a study. Using data from almost 900 measuring points in Austria, it was possible to prove that the amount of rain that has fallen within one day during extreme weather events has increased by 8 percent over the last 40 years. The risk of small-scale flooding has even increased by 25 percent in the same period, explain the experts in the analysis just published in the scientific journal "Nature". The evaluations have global relevance, especially for mid-latitudes.

The study was carried out in cooperation between the Federal Ministry of Agriculture, Forestry, Regions and Water Management (BML), the Vienna University of Technology, GeoSphere Austria and the University of Graz. Evaluations of the recordings at almost 900 measuring points show that short-term, extreme rainfall has increased since the 1980s and that the figures also correspond to the increase in flood events. The measuring points, some of which provide data on an hourly basis, made it possible to analyze measurement series between 1900 and 2023. According to the hydrologist involved in the study, Günther Blöschl from the Vienna University of Technology, this is unprecedented.

Connection between heavy rainfall and global warming

"From 1950 to 1980, the hourly values of heavy rainfall show no trend. In the 40 years from 1980 to the present, the amount of heavy rainfall increased by around 15 percent," says Klaus Haslinger from GeoSphere Austria, lead author of the study: An average heavy rainfall in the period 2003 to 2023 brought 15 percent more water than an average heavy rainfall in the period 1950 to 1970."

"This shows that global warming is primarily responsible for the increase in hourly heavy rainfall," says climate researcher Haslinger, "for every degree of warming, air can absorb around seven percent more water vapor, as shown by a physical law defined by the Clausius-Clapeyron equation. The last 40 years have brought a warming of around two degrees in Austria, which corresponds almost exactly to the 15 percent increase in heavy rainfall determined from the station measurements."

"This also means that this happens more or less everywhere outside the tropics in a similar way. This is the first study in the world to show this," says Blöschl, explaining the TRagweite of the study results

Risk of small-scale flooding increases by 25%

In particular, the accumulation of short, intense rainfall has increased the risk of flooding in small catchment areas over the past four decades (around 25 percent in the last 40 years). This development is a consequence of climate change: higher temperatures allow the atmosphere to store more water, which favors extreme precipitation.

For the first time, the direct link between climate change and pluvial flooding has been clearly demonstrated by reliable measurements. Pluvial flooding occurs when it is triggered by heavy rainfall.

Existing measures and further research

In order to minimize the effects of increasing heavy rainfall events and surface runoff, initiatives such as a comprehensive hazard information map and a guide to self-caution in the event of surface runoff as well as the promotion of measures to retain surface runoff and prevent soil erosion have been implemented for several years.

Particularly in small catchment areas, where technical flood protection can only partially contribute to reducing the flood risk, individual precautions play a decisive role. Here, heavy rainfall events are often so localized and variable that general protection measures reach their limits and the possibilities of spatial and building regulations as well as disaster control must be given greater consideration in order to ensure comprehensive flood risk management.

Link

The study "Increasing hourly heavy rainfall in Austria reflected in flood changes" was published this week in the scientific journal "Nature" : (link to the article).