Make Your Mind Up: Is it Floods or Drought that’s the problem?

To name just some of the horrific flood events from the last few weeks: The East Coast of USA; Nepal; Central Europe; Central England; Hurricane Helene; Storm Boris; and – as I write – Hurricane Kirk (mental note: good excuse to make a Star Trek reference later). Given that I regularly write about water scarcity – and the first Water Matters podcast was on the topic of ‘Day Zero’ and cities running out of water – how can we have both water shortages and a flooding problem? Surely one solves the other? Well, not quite. Water scarcity and flooding are two sides of the same coin. The good news is, they share many of the same solutions, too.

Trying to prove that climate change caused an extreme weather event such as Hurricane Helene is difficult. Albeit there is a whole new strand of climate science called Attribution Studies which attempts just that. But proving that climate change made Hurricane Helene stronger and more devasting is comparatively straightforward. A warmer climate creates more evaporation, holds more water vapour in the atmosphere, and causes more intense rainfall. It’s the water cycle, Jim, but not as we know it – it’s speeded up. In fact, 7% more moisture is added into the atmosphere for each 1°C rise in global mean temperature. Given that the world has already warmed by over 1.1°C since preindustrial times, and hit the grim milestone of 1.5 degrees this summer, this means more fuel in the atmosphere for intense storms. It also means more evaporation from the land, leading to drier, parched earth – exacerbating flood conditions when the (heavy) rains return.

In short, the new normal sees us increasingly yo-yoing between flood and drought. UN Water reports that the number and duration of droughts has increased by 29% since the year 2000, while flood-related disasters have increased by 134%. It rains less frequently because it’s held in the atmosphere for longer, but when it does rain, it dumps out in ever-more intense volumes. As any farmer or amateur back-garden weather station enthusiast can tell you, we’re getting roughly the same amount of rain annually, but it’s less evenly dispersed.  The ‘driest month of X ever’ is often followed by the wettest ‘month of Y’.

All of which makes water management far harder. I remember my surprise when getting a tour of Farmoor reservoir one similarly wet October – I had expected the water engineers to be pleased with all the recent rain, but in fact they closed the levees that feed into the reservoir on such days. The river Thames would be too murky, apparently. It was not “the right kind of rain”.

Much of our water engineering is still Victorian, either literally or in mindset. Between 1840-1890, 12 million acres of land were drained in the UK, adding levees, embankments and dredging, re-channelling and straightening rivers to meet drainage and commercial shipping needs. Stormwater was to be channelled out to sea as quickly as possible. Large reservoirs and dam walls could deal with the rest.

That system is no longer fit for purpose. We have disconnected our waterways from their underground water sources and floodplains – meaning we no longer have the water we need in summer (see ‘Day Zero’). And from a flood management perspective, losing the sponge effect of floodplains and wetlands was catastrophic. Concrete flood defences cannot compete with the intense rainfall events we’re now seeing both locally and globally.

That rivers should be winding, with floodplains, marshlands and ponds, sounds like an environmental message. But it is for the benefit of human communities, too.

In the 2010s, following years of damaging flood events, the town of Pickering in Yorkshire came close to spending £20m on concrete flood defences. Instead they went ahead with a plan that promised to be more effective, at a tenth of the cost: rewilding and restoring the river upstream, to slow and absorb flood water before it reached the town. The following year, when flooding hit North Yorkshire again, Pickering was one of the few towns in the area that came out unscathed.  

The successful measures Pickering introduced included restoring floodplains, and constructing ‘leaky dams’ – essentially logs and branches laid across the river, mimicking how the UK’s wild rivers would once have been. Currently, such log dams are handmade by volunteers. But recent work to reintroduce beavers would make better leaky dams without the time or labour costs (but that’s another blog for another day!)

We do still need engineered flood defences. But think about it this way, as one conservation manager put it: “if you can slow things down upstream you don’t need to build your walls so high.”

In the Lake District, a re-meandering scheme in the Swindale valley for just £200,000 let the river meander back into its old course after being straightened by hill farmers: each 1km of river in the valley is now 180 metres longer, with ponds and floodplains – it’s not hard to see how that would slow, hold and absorb more water River floodplains restored to their natural status have been described by the National Trust as “a computer reset” of our river systems.

But what does that look like in our towns and cities, where ‘rewilding’ in any meaningful sense is no longer possible? It means Sustainable Urban Drainage Systems (SuDS), parks and trees, pervious pavements, green walls and green roofs, all designed to soak up and soak in the stormwater. Even Xi Jinping is a fan. China’s ‘Sponge City’ initiative has spent billions on the greening of Chinese cities as a flood defence and water capture strategy since 2015. The ongoing plan is to absorb, reuse or recharge 70 per cent of the rainwater on four fifths of China’s urban land.

Arguably the UK will have its own “sponge city” when Mansfield’s £76m SuDS retrofit scheme completes in 2025. The scheme will store more than 58 million litres of surface water, equating to a reduced flood risk for 90,000 people – almost the entire population. Severn Trent told New Civil Engineer magazine that, “The Mansfield SuDS is effectively a scheme based on how we want to manage surface water differently in the future”.

Rainwater harvesting tanks are also a SuDS technique, from garden water-butts to rooftop tanks and underground units. When I spoke to Dr Peter Melville-Shreeve at Exeter University for my book The Last Drop, I remember him telling me that “there's a larger holistic benefit to having a rainwater system for stormwater management than for the free water benefit.” In new-build housing developments, he said, if you installed appropriately functioning rainwater harvesting systems, “you can chop your stormwater runoff in half because you've captured it off the roof”.

Between 2018 and 2020, South West Water gave Peter funding for a proof-of-concept pilot on a hundred properties in St Mary’s, the Isles of Scilly. The year-long pilot evaluated the benefits of rainwater collected from the house roofs and stored in 600–1,000L tanks, internet-connected using Peter’s own patented system which communicated real-time data. When the tanks were full, any additional rainwater spilled back to the drainage system; and, if the tanks ran empty during dry periods, they would automatically top-up with mains water, meaning that householders never noticed a change in service level (what Peter calls ‘fit and forget’).

Peter’s system could even drain the tanks in anticipation of a major storm event, to avoid overwhelming the sewers. The water savings alone – not even taking into account the wastewater and storm-water benefits – came to a staggering average saving of 54 L per day, per house (20,000 L per year). But there was also far less run-off to overwhelm the sewage system – the very overwhelm that water companies have blamed for the sewage crisis.

Thames Water want to build southern England largest ever reservoir in Abingdon, which will take 10 years to build and just as long to fill. I believe that is now the wrong approach. As the University of Ghent proclaimed in 2015, “The next big thing will be a lot of small things”. Big, centralised systems are not climate resilient. We need a mass movement to build and restore the small things: parks, trees, rivers, wetlands, floodplains, SuDS and rainwater harvesting tanks. Combined, these form the solution to the water crisis: both flooding and drought.