Rivers may see more frequent floods and droughts due to climate change

By Stephen Beech

British rivers may see more frequent floods and droughts due to climate "whiplash," say scientists.

Global warming could push U.K. waterways to dangerous extremes — a phenomenon known as "hydroclimatic whiplash" which will see more rapid swings between wet and dry conditions, according to a new study.

A research team, led by University of East Anglia (UEA) scientists, analyzed almost 700 river catchments across the British Isles to project how river flows may change at 2 and 4 degrees Celsius of global warming.

The results, published in the journal Earth's Future, reveal "stark" regional contrasts and growing challenges for communities and water managers trying to plan for flood and drought risk.

The researchers also warn of more intense river flooding during extreme rainfall events in western and northern parts of the U.K. and longer dry spells and lower river flows in southern and eastern England.

They say the findings underline the need for regionally tailored adaptation, including enhanced flood-risk management and greater capacity to store water during wetter periods in western and northern parts of the U.K.

The study also highlights the need for strengthened water-supply resilience and demand management in southern and eastern England, according to the research team.

Study lead author Dr. Yi He said: “Our projections show sharper swings between heavy downpours and long dry spells, with river catchments shifting more suddenly from flooding to drought.

“These rapid shifts are making water management increasingly difficult, putting pressure on both flood defenses and drought-response systems at the same time.

“As warming increases, traditional approaches to flood and drought planning may no longer be enough.

"Instead, region‑specific adaptation strategies will be critical to protect water supplies, infrastructure, ecosystems, and communities.

“Climate change is expected to increase both floods and droughts in many regions, so understanding how these changes will play out locally is crucial for managing water resources and preparing for future risks.”

She says dry-to-wet hydroclimatic whiplash — sudden shifts from dry to wet conditions — may increase the risk of flash flooding, water quality deterioration and soil erosion.

Wet-to-dry shifts can make drought planning harder because preceding wet conditions may create a false sense of security before a rapid move into drought.

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Projected changes under both 2- and 4-degree warming scenarios show widespread increases in the frequency of both types of whiplash events.

For dry-to-wet whiplash, increases are projected across most of the U.K.

In some catchments, the number of events rises from around four over a 30-year period from 1981 to 2010 to around seven to nine under 4-degree warming.

Overall, stronger increases can be observed in South Wales, Northern Ireland, Northern and Western England and parts of Southeast England.

The modeling provides one of the most comprehensive national-scale assessments to date of how U.K. rivers may respond to different levels of global warming.

The results also show how temperate climates worldwide could face similar shifts.

Under baseline conditions between 1981 and 2010, the middle value across U.K. catchments for the maximum number of consecutive dry days — an indication of heightened drought risk or conditions associated with drought — is 32.

But that number rises to 36 days under 2-degree warming and 41 days under 4-degree.

The most pronounced increases are seen in southern and Southeast England, including the Anglian, Thames, and South East river basin regions, where the maximum number of consecutive dry days could exceed 50 days under 4-degree warming.

Catchments in northern and western Scotland show smaller increases, remaining below 35 days even under the highest warming scenario.

But western and northern parts of the U.K. — including Wales, Northwest England, western Scotland and parts of Northern Ireland — are projected to see the largest increases in flooding and extreme rain, with the strongest rises in extreme rainfall linked to upland and Atlantic-facing catchments.

The largest increase is projected for the Glaslyn at Beddgelert catchment in Snowdonia, North Wales, where maximum one-day rainfall rises by more than 30 mm and maximum five-day rainfall by almost 42 mm under 4-degree warming.

For river flooding, the study finds that the size of a flood with a 2% chance of occurring in any given year — often called a 1-in-50-year flood — generally increases across U.K. river basin regions.

The projected increase is around 20% to 50% under 2-degree warming and up to 40% under 4-degree warming, with greater regional variation and uncertainty at the higher warming level.

He, of the Tyndall Centre for Climate Change Research at UEA, said: “The U.K.’s well-monitored river network and strong regional climate contrasts make it an important test case for temperate regions worldwide."

She added: “Our findings offer insights into how global warming could alter river flows, flood and drought risks, and rapid shifts between wet and dry conditions beyond the U.K.”