As the world becomes increasingly impacted by climate change, understanding more about the potential future intensity of hourly rainfall and extreme daytime temperatures is key to the UK’S resilience.
The Met Office and the Environment Agency have launched the highest-ever resolution of climate projections produced for the UK, which is on par with the resolution used for weather forecasting. The launch complements the other products already unveiled last year as part of the UKCP18 suite of climate projections. In the coming decades, extreme weather events, such as higher maximum daily temperatures and intense rainfall events, which may lead to flash flooding, are said to be some of the most serious potential consequences of climate change set to affect the UK.
The Met Office scientists have divided the UK up into 2.2km grid squares to provide higher resolution projections and an improved representation of small-scale features, such as the development of thunderstorms and the influence of mountains, coastlines and cities. In addition, the science team has been able to look at weather events that will only last less than a day which will provide new information that will be essential for understanding flood risk.
The 2.2km model suggests that in the future, there will be significant increases in hourly rainfall extremes. For example, rainfall associated with an event that occurs typically once every two years, increases by 25% by the 2070s under a high emissions scenario – a level where insufficient global action has been taken to reduce the atmospheric concentration of greenhouse gases. These projections use the RCP8.5 emissions scenario, which relates to a change in global temperature of around 4.0 C by the 2070s, relative to the period 1981-2000.
The frequency of days with hourly rainfall exceeding 30 mm per hour – the threshold used by the Environment Agency to indicate likely flash flooding – almost doubles by the 2070s under a high emissions scenario – increasing from a UK-average of once every ten years in the present-day to almost once every five years by the 2070s.
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