Rising temperatures may increase flood risk through river ‘whiplash’, study finds | Climate crisis

Rising temperatures could trigger a dangerous increase in the “hydroclimatic pulse” on rivers, making traditional approaches to flood and drought planning inadequate, a study has found.

As temperatures rise due to the worsening climate crisis, rivers will experience increasingly rapid shifts between heavy downpours and long droughts, called hydroclimatic whiplash events, as a warmer atmosphere will retain more moisture, intensifying extreme precipitation.

The study found that sudden transitions from dry to wet conditions can increase the risk of flash flooding because heavy rainfall on dry, hardened soil is less likely to penetrate the ground. Instead, water can rush off the surface, causing localized flooding and deterioration of water quality, as well as soil erosion as heavy rainfall washes pollutants into rivers.

By comparison, transitions from wet to dry can make drought planning difficult because previous wet conditions can create a false sense of security ahead of a rapid transition into drought.

In the study published Wednesday in Earth’s Future, Researchers used climate projections and a hydrological model to simulate changes in 698 river catchments in the UK under 2C and 4C warming scenarios. In the study, hydroclimatic whiplash was defined as a movement of monthly river flow from unusually low flow to unusually high flow or vice versa.

Lead author Dr Yi He from the University of East Anglia said the UK was already experiencing rapid transitions from dry to wet and wet to dry, making hydroclimatic impact a significant concern.

Modeling, which provides the most comprehensive national-scale assessments to date of how UK rivers may respond to different levels of global warming, found widespread increases in the frequency of whiplash events of both types (wet to dry and dry to wet) are expected in the 2C and 4C warming scenarios.

The researchers found that in some basins, the number of whiplash events could increase from about four over a 30-year period in the 1981-2010 baseline to as many as nine under a 4C warming scenario.

Although this increase is predicted across much of the UK, the largest increases in dry-wet whiplash are likely to occur in south Wales, Northern Ireland, northern and western England and parts of south-east England.

Dr He said these rapid changes would also put pressure on flood defense systems and drought response systems, making water management increasingly difficult. “As warming increases, traditional approaches to flood and drought planning may no longer be adequate,” he said. “We need to plan for extraordinary circumstances, not just one event.”

The study’s authors said the findings underscore the need for regionally tailored adaptation plans, including improved flood risk management and greater capacity to store water during rainy periods.

Dr He said modeling in the UK was an important test case for temperate zones around the world, and the findings offered insights into how rising temperatures could alter river flows and flood and drought risks around the world.