Abstract
High impact weather events such as extreme temperatures or rainfall can cause significant disruption across the UK affecting sectors such as health, transport, agriculture and energy. In this study we draw on the latest set of UK climate projections, UKCP, to examine metrics relating to high-impact weather over the UK and how these change with different levels of future global warming from 1.5 °C to 4 °C above pre-industrial. The changes to these hazards show increases in the frequency of extremely hot days and nights, with a UK average increase in hot days of between 5 and 39 days per year between 1.5 °C and 4 °C of global warming. Projections indicate an increase in cooling degree days of 134–627% and an increase in growing degree days of 19–60% between 1.5 °C and 4 °C of global warming. Extremely hot nights, which are currently rare, are emerging as more common occurrences. The frequency of high daily temperatures and rainfall increase systematically, while the frequency of very cold conditions (based on days where temperatures fall below 0 °C) is shown to decrease by 10 to 49 days per year. A reduction in heating degree days, of 11–32% between 1.5 °C and 4 °C of warming, is projected. Levels of daily rainfall, which currently relate to increased risk of river flooding, are shown to increase across the country, with increases of days with high impact levels of rainfall occurring by 1 to 8 days per year between 1.5 °C and 4 °C of warming. Average drought severity is projected to increase for 3-, 6-, 12- and 36-month-long droughts. The largest changes in the severity of the 12-month drought are between −3 and +19% between 1.5 °C and 4 °C of warming and for 36-month drought between −2 and +54% between 1.5 °C and 4 °C of warming. The projected future changes in high impact weather from this study will enable the characterization of climate risks and ultimately be able to better inform adaptation planning in different sectors to support the increase in resilience of the UK to future climate variability and change.
Highlights
Human and natural systems can be vulnerable to weather and climate variability, and it is clear that extreme weather events can cause impacts across many sectors in the UK
We have presented a range of impact relevant hazard metrics derived with respect to fixed global warming levels and using the new UKCP regional model dataset
The results reinforce the view from the second UK Climate Change Risk Assessment (CCC 2017) of the potential for severe impacts on the UK from changes in precipitation, leading to both flooding and drought and extremely high temperatures
Summary
Human and natural systems can be vulnerable to weather and climate variability, and it is clear that extreme weather events can cause impacts across many sectors in the UK. Attribution studies have shown that UK heatwaves, such as that of summer 2018, could be 30 times more likely due to anthropogenic activities (McCarthy et al 2019). Results from the latest set of climate projections for the UK (Lowe et al 2018) estimate that summers like 2018 could be “more common than not” by the mid-twenty-first century. To illustrate the severity of this particular extreme event, summer 2018 saw a hot, dry spell in June and July 2018 which resulted in a range of heat-related impacts due to high daytime temperatures:
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