After a record-breaking summer - and with a potentially very strong El Niño developing - Jon Fawcett, Head of Technical at Keyline Civils Specialist, reflects on how the changing climate is contributing to surface water flooding.
With Flood Action Week underway, it seems timely to talk about how and why the extreme weather we’ve been experiencing is worsening surface water flooding.
Flooding of all kinds has been a growing concern for several years. To mark the start of Flood Action Week 2026, the Department for Environment, Food & Rural Affairs (Defra) and the Environment Agency have launched ‘Flood Action Online’, which the government describes as a “one stop shop” for flood preparedness in England.
It brings together guidance on checking your flood risk, signing up for flood warnings and Met Office weather alerts, and measures that can make properties more resilient to flooding.
Flooding of any kind can have a devastating impact on people’s lives, and with £4.2 billion being invested in flood defences between 2026 and 2029, it’s clearly not a problem that is going away. Surface water is the most widespread risk: the Environment Agency estimates that around 4.6 million of the 6.3 million properties at risk of flooding in England are in areas at risk from surface water.
This is likely to be compounded by El Niño. The Met Office has said this year’s event could be the strongest since the 19th century, and that the UK is likely to see wetter and stormier conditions this autumn and into early winter.
It might seem counterintuitive, but the longer spells of hot and dry weather we’re experiencing are also contributing to surface water flooding.
After a prolonged hot spell - and this summer was the UK’s warmest on record - it can be a relief to see some rainfall. But through a combination of natural and man-made factors, while a downpour may be good for the garden, there’s an increased risk that it can lead to surface water flooding.
Surface water flooding occurs when rainfall cannot drain away quickly enough. Often this comes down to something as simple as gullies, drains or culverts blocked by leaves and debris, or a lack of available capacity in existing drainage.
There are, however, a few more recent factors making the situation worse.
Firstly, growing urbanisation means more hard, impermeable surfaces - whether that’s new roads to connect up housing developments, front gardens paved over for driveways, or natural grass replaced with artificial alternatives.
Secondly, a warmer atmosphere holds more moisture - roughly 7% more for every 1°C of warming - so when the hot weather breaks, we can see shorter but more intense downpours.
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The issue here is that the ground is often baked hard by then, so when it gets hit by a sudden deluge, the soil can’t absorb the water quickly enough and much of it runs off or pools on the surface.
Thirdly, all of this is feeding into drainage networks, many of them decades old, that were not designed to handle these volumes, both in terms of the additional surface water runoff and the growing number of new properties connected to them.
And all of this comes on top of longer periods of rainfall during the autumn and winter months, when the ground becomes saturated and can absorb little more, meaning that once again there is a considerable risk of surface water flooding.
This type of flooding can form rapidly and its impacts can be severe, from costly insurance claims and repairs to significant disruption for homes and businesses.
This is why it’s more important than ever to ensure that drainage is capable of dealing with increased volumes of surface water.
That can mean managing water closer to where it falls, through sustainable drainage (SuDS) features that slow, store and, where ground conditions allow, infiltrate runoff; providing attenuation storage that holds water back and releases it at a controlled rate, easing pressure on existing sewer networks; or building additional capacity into new and existing sites. Just as important is maintenance - keeping gullies, channels and culverts clear so that existing systems perform as intended.
So while the government invests in defences and helps people to prepare, those of us in the drainage and civils sectors should be looking to the future, and considering new and better ways of managing what can be a life-changing issue.