Heavier summer downpours possible due to climate change

The study, know as the CONVEX project, uses a state-of-the-art climate model that has provided the first evidence that hourly rainfall rates in summer could increase.

Even though it is expected that summers by 2100 will be drier than they are now, intense rainfall rates, of the type that cause flash flooding, could occur several times more frequently.

Dr Lizzie Kendon, lead author of the research at the Met Office, said: “It shows heavier summer downpours in the future, with almost five times more events exceeding 28mm in one hour in the future than in the current climate — changes we might expect theoretically as the world warms.”

She added: “However, we need to be careful as the result is only based on one model – so we need to wait for other centres to run similarly detailed simulations to see whether their results support these findings.”

The research is an important step in understanding how UK rainfall will change in a warmer climate – especially when looking at past events such as the Boscastle flooding in 2004.

Until now, climate models haven’t been able to simulate how extreme hourly rainfall might change in the future, due to limitations of computing power and model resolution.

The study uses a climate model with a higher resolution than anything used before. Instead of the previous grid box resolution of 12km, a 1.5km resolution has been used.

This has allowed much more detail to be gained, offering scientists a realistic representation of hourly rainfall and the ability to make future projections with some confidence.

The study was so computer intensive that only the southern half of the UK could be included. Even then, it took the Met Office supercomputer – one of the most powerful in the world – about nine months to run the simulations.

Two 13-year periods were looked at, one based on the current climate and one based on the expected climate around 2100.

Prof Hayley Fowler, from Newcastle University’s School of Civil Engineering and Geosciences, and lead on the CONVEX project, said: “The next steps are to see if these changes are consistent with observed trends in summer rainfall extremes and changes projected by climate models in other parts of the world. We will be looking at this over the next five years, jointly with the Met Office and other leading international scientists in the European Research Council funded INTENSE project.”

A warmer atmosphere can hold more moisture and this is expected to intensify rainfall. This ongoing research is needed to understand what this might mean for extremes and how this might affect the UK.