FloodsFlash Flooding Is a Serious Threat in the U.K. – Here’s How Scientists Are Tackling Its Prediction
Surface water flooding is what happens in built-up areas when heavy rainfall has nowhere to go. Unable to enter a watercourse or drainage system, the water instead flows over the ground causing flash flooding. Unlike river and coastal flooding, which can be widespread, surface water flooding presents unique challenges because it’s difficult to predict the location, timing and impact of what are typically localized events. As the climate changes and urban populations grow, the number of people at risk of surface water flooding increases.
It’s becoming a familiar scene on the news: sodden British people wading through streets up to their knees in flood water. From Stirling to Sheffield, many parts of the UK in 2019 felt the impact of severe surface water flooding – often referred to as flash flooding – that followed torrential rain. As the climate changes and the UK experiences more intense summer storms, this is becoming an increasingly important issue.
Surface water flooding is what happens in built-up areas when heavy rainfall has nowhere to go. Unable to enter a watercourse or drainage system, the water instead flows over the ground causing flash flooding. Increased development means more areas are paved over, leaving fewer places for rainfall to drain away. And more frequent heavy rains overload the sewer and drainage network, which makes flash flooding more likely.
James Bevan, chief executive of the England and Wales Environment Agency, said this kind of flooding “threatens more people and properties than any other form of flood risk”. In 2016, the UK government included surface water flooding on the national risk register.
Unlike river and coastal flooding, which can be widespread (as was seen in November 2019 across parts of northern England), surface water flooding presents unique challenges because it’s difficult to predict the location, timing and impact of what are typically localized events.
As the climate changes and urban populations grow, the number of people at risk of surface water flooding increases. This risk is particularly high in Scotland with over 100,000 properties identified at risk from flash floods. And for many people, even if their home or business is not at risk, there’s a good chance the roads or railway lines they use are.
Flash Flood Forecasting in Scotland
Although Scotland’s river and coastal flooding warning systems are well established, surface water alerting is still in its infancy. To address this gap, the Scottish Environment Protection Agency (SEPA) is continually developing its flood forecasting service with the Flood Warning Development Framework for 2017-21, which aims to explore and test innovative ways to warn people about flash floods.
Developing an effective forecasting system requires hydrological models that represent surface run-off, inundation and water movement, showing how water travels via surface and urban sewerage and drainage networks. Prediction models are also needed to quantify uncertainty in forecasting the rainfall that causes surface water flooding.
