Environmental (Commonwealth Union)_ The familiar rhythm of British weather is disintegrating. Once, the nation could expect a broadly dependable seesaw between damp summers and more waterlogged winters, but now it is swinging wildly from one end of the spectrum to the other: hosepipe bans for 8 million households in spring droughts and then biblical floods the next season. This hydrological fluctuation, the more extreme pendulum swings between water deficit and excess, constitutes one of the most paradoxical impacts of climate change in the UK. While climate models all agree with a drier future with more severe droughts, observational data provides a more complex and contradictory story of an evolving climate system, one that is moving rather than following a simple linear path.
Spring and summer 2025 have proved extremely enlightening. The Derwent and Wye rivers dropped to levels equaling or even below the legendary 1976 drought, the long-time benchmark for water scarcity. But these droughts have been punctuated by bouts of heavy rain and flooding, which have triggered a whiplash effect, straining both water systems and environmental systems. The Environment Agency’s maps tell a spatially complex story too: while southeastern rivers show decreasing flows, many northern and western waterways have actually seen increases in their minimum flows over the past half-century. This north-south divergence reflects both the influence of natural climate oscillations like the North Atlantic Oscillation and the uneven fingerprint of global warming across the UK’s varied landscapes.
Climate projections paint a concerning future. According to the high-emission RCP8.5 scenario, hydrological models anticipate uniformly declining summer river flows in all UK catchments by the 2080s. The lowest value annual flows are expected to decline significantly, particularly in the summer, suggesting more severe and frequent hydrological droughts. But these open projections contradict the record of observation: no systematic trend of worsening droughts in the past 50 years, and even longer reconstructions back to 1890 show no linear evolution towards dryness. This apparent contradiction arises because natural climate variability, like events such as ENSO and NAO, can mask underlying trends over decades in a country as hydroclimate-complicated as the UK.
The real concern for water managers is not so much the direction of increasingly recurrent summer droughts superimposed on increasing temperatures (although the latter are undesirable enough) but the probability of multi-annual droughts energised by back-to-back dry winters. Previous droughts, such as those from 1988 to 1993 and 2010 to 2012, which persisted for two or more years, have been particularly challenging for the water supply. Even though climate models generally indicate wetter winters, climate variability guarantees that sequences of dry winters will continue to occur. The greatest vulnerability of the water supply is the combination of dry winters and hot summers, which was exactly what caused the 1976 drought.
This hydrological uncertainty demands a new approach to water management. Rather than building water systems against past averages or waiting for unambiguous trends, water systems must be stress-tested against the entire spectrum of possible futures in large ensembles of climate models. The UK must plan simultaneously for both dry and wet extremes, investing in flood resilience and water storage and transfer infrastructure. The alternative is to be locked into a perpetual cycle of reaction: imposing hosepipe bans during droughts, then scrambling months later to cope with floodwaters, all the while the underlying climate ineluctably changes towards ever greater extremes. British weather is not just changing; it’s going through an identity crisis, and water management must change to cope with its new contradictory nature.
