The UK had the driest start to a year since the 1970s in 2022, with large parts of southern England receiving less than 50% of their normal winter rainfall. On top of that, southern England recently received just 17% of its average rainfall for July, in what was the country’s driest since 1935.
How the atmosphere circulates moisture is incredibly complex and so there is huge variability in rainfall from year to year. This makes it very difficult to conclude trends from past observations.
Temperature trends, meanwhile, are more straightforward: increasing concentrations of greenhouse gases in the atmosphere have raised average temperatures and made dry periods in Britain drier, as hotter weather evaporates more water. Short and intense rainfall, which does not replenish parched soils, rivers and aquifers as well as gentler, longer showers, is also increasingly common as warmer air can hold more moisture.
Although some water companies have enacted hosepipe bans to conserve water in the worst-affected areas, the Environment Agency has yet to declare an official water supply drought. Reservoir levels were healthy entering 2022, having been replenished in the preceding autumn, but some in southwest England are now less than half full.
Farmers across southeast England have been reeling from an agricultural drought (when levels of moisture in the soil are low enough to affect crop production) since spring. Warmer than average summer temperatures, plus a heatwave during which temperatures reached 40°C for the first time in the UK, have further dried out the soil.
At the time of writing, many rivers across southern England are exceptionally low. The situation could significantly worsen if a dry autumn or winter follows.
Rivers with underlying acquifiers in southern England (such as chalk streams) can take months to respond to changes in rainfall. Projections by the UK Centre for Ecology and Hydrology suggest that flows will remain below average in these groundwater-fed rivers over autumn and potentially beyond.
Yet, the UK retains its reputation for being a rainy country. A survey titled The Great British Rain Paradox conducted in 2020 showed that 77% of the British public agreed with this sentiment. But with most of the UK forecast to have hotter and drier summers, it’s no longer as simple as that.
The Great British rain paradox
The UK has experienced regular periods of drought in the past, including the last official drought in 2018-’19. The National Infrastructure Commission, which advises the government, warned then that the UK must do more to prepare for water shortages. The Environment Agency estimates that water demand may outstrip supply across southern England in as short a timescale as 20 years if the country does not adapt to its new climate by building reservoirs and desalination plants.
So what does that new climate look like? The latest set of simulations project hotter and drier summers plus warmer and wetter winters, with larger changes in summer compared to winter rainfall.
Prolonged periods of below average river and groundwater levels are projected to become more severe. Summer droughts are likely to affect the entire country, while multi-year droughts are more likely across southern England.
There will be an increased risk of cascading hazards in future too, such as when a flood quickly follows a drought, spoiling crops and damaging infrastructure. Record rainfall in spring 2012 suddenly ended a drought which had begun in 2010, causing flash floods which affected more than 4,000 properties.
How low rivers and public water supplies recede each summer will depend on rainfall in autumn and spring. There is less agreement between climate model simulations on how rainfall patterns will change in these seasons, which is when aquifers are usually replenished. Water demand will add an additional strain on these sources as the population grows, particularly as severe heatwaves are set to become much more common.
Severe droughts in the UK’s past have always included one or more dry winters, such as 1975-’76, 1988-’93 and 2010-’12. The severity of future droughts will be determined by how sequences of dry seasons interact.
Research has shown that the probability of a dry winter and spring being followed by an extremely hot summer, like the one the UK is experiencing in 2022, is now at least five times more likely compared with the 1970s. A drier than average winter is much more likely to be followed by a dry summer too.
Although winters are projected to become wetter on average, scientists aren’t sure how the sequencing of dry seasons is changing. This is due to uncertainty around the influence of climate change on atmospheric circulation, such as the position and strength of the jet stream – a major driver of heatwaves and dry weather in the UK.
Where the rain ends up falling also matters. The northwest of the UK, including Northern Ireland, receives more rain than the southeast. So a wet winter nationally could still mean drier than average conditions in the southeast.
Water companies cannot discount the possibility of consecutive dry winters and the potential for three consecutive dry winters are particular concern. This was narrowly avoided in the 2010-2012 drought, but research has revealed that continued dry conditions in 2012 would have meant critically low river flows across southern England.
To prepare for a drier future, the UK must reckon with the ways drought will make food production, biodiversity conservation and even electricity generation (as a result of cooling water shortages and reduced hydro-electricity) more difficult. Droughts will have major implications for the country’s national food strategy, its nature recovery targets and – critically – progress towards net zero emissions, which will be essential for bringing extreme weather under control.
This article first appeared on The Conversation.