Extraordinary scenes unfolded across Birmingham this Spring Bank Holiday as the city was battered by a huge downpour of rain.  We examine the origin of this spectacular storm system and compare the impact of the city’s flash flooding against our risk models.

The Met Office recorded a month’s worth of rain in just an hour, with 58.6mm falling in parts of Edgbaston and 81mm in a 12-hour period. The very warm air pulse drew up a very warm southerly air stream from eastern France into South Eastern UK, creating rising, unstable cloud formations, which built to extensive cumulonimbus storm cells.

These storms can last for several hours if there is enough energy and moisture to sustain the process and can form a large complex of thunderstorms known as a Mesoscale Convective System (MCS). This was how the situation developed over the Bank Holiday Weekend, with the UK as a whole recording over 100,000 lightning strikes.

Roads Become Rivers

As the system picked up heat and moisture from the English Channel and the South East, it accelerated its electrical charge and rainfall load. It delivered spectacular lightning displays and discharged a huge amount of rainfall in a track from Northamptonshire, through the West Midlands and onto the Welsh Borders.

Dramatic footage captured the effects of the flash floods across Birmingham. Homes were severely flooded on Sir John’s Road, Selly Park, with wheelie bins floated past submerged cars, as roads became rivers.

More than 100 homes were flooded in June 2016 on the same street, forcing evacuation of the residents. The nearby Heartlands Hospital declared a major incident when its accident and emergency department was badly hit.

Some residents had only recently returned before Sunday’s floods. The Far Cotton area of Northampton was also severely flooded, with the M1 and A45 under three feet of water in places.

The Environment Agency issued 28 red “immediate action required” flood warnings for parts of the Midlands, as smaller rivers reacted rapidly to the torrential rain. The situation was compounded by severe surface water flooding in some places.

Cities Failing to Cope with Surface Flooding

These storm cells are becoming ever more frequent, as our atmosphere warms up through Climate Change. Increasingly higher amounts of moisture are being generated which creates locally very severe surface water flooding. The run-off charges sewer systems and often small, usually benign streams impacting houses and community services at a very local level, with little warning.

Urban areas like Birmingham have large swathes of hard concrete surfaces, with few areas for surface water to naturally drain, exacerbating flooding where events occur across our cities. In the face of such localised intense rainfall, our urban streetscapes are least capable of dealing with the deluge.

The above image shows pluvial (flash flood) predictions from Ambiental’s UKFloodMap4™ hazard data. This flood data layer (shown in pink) shows areas susceptible to flooding from intense rainfall and corresponds with reports of flooding near Selly Park, Birmingham. You can see how precise the modelled flood extents are – together with how the roads funnel and increase the surface flooding risk. Find out more information about Ambiental’s flood maps here .

Ambiental’s FloodFutures® modelling helps insurers, property and infrastructure asset managers with long term planning for resilience. We are developing flood forecasting systems, such as FloodWatch® to support countries around the world which can model flash flooding. Contact us to find out more.