The influence of future weather pattern changes and projected sea-level rise on coastal flood impacts around the UK

Abstract

When local extreme water levels surpass defences, the consequences can be devastating. We assess the importance of sea-level rise and future weather pattern changes on UK coastal flood impacts. Historical weather pattern classifications are matched with the observed skew surges and significant wave heights. Coastal-risk weather patterns are then defined as ≥ 1% of events in the distribution exceeding the local warning threshold. We combine this methodology with projections of sea-level rise and weather pattern frequency occurrences, to determine the relative importance of each on future coastal risk. A deep low-pressure system situated to the west of Ireland (WP29) has the highest probability (6.3%) of exceeding Newlyn’s present-day warning threshold; this is projected to increase under climate change to 46.2% by 2050 under RCP2.6. This work found that weather patterns associated with storm surges are increasing and decreasing in frequency; a synoptic situation causing windy conditions in the north of the UK (WP23) will increase by > 40% under RCP8.5 by the end of the century (2079–2090). When combining the impact of sea-level rise and changing frequency of weather patterns, this study found that sea-level rise dominates future coastal risk and is highly linked to the future emission scenarios. The need for successful adaptation, such as coastal defence improvements and early warning systems, will become even more important under the higher emission pathway. The most significant increases in coastal risk are found along the east coast, through the English Channel to the north Devon coastline.

Synoptic conditions conducive for compound wind-flood events in Great Britain in present and future climates

“…The location of most extreme precipitation in the future period is centred over Southern England (as reported in [43]), suggesting extreme rainfall may now coincide with locations of potential wind damage (see figure A4). This is also a region experiencing increased coastal flood risks, associated with sea level rise [45]. Storms are generally present around GB for the compound windflood events, although in a future climate it becomes more common for the minimum MSLP to be over the North Atlantic (see figure A5).…”

Storm surge changes around the UK under a weakened Atlantic meridional overturning circulation

“…As part of a wider study which considers projected change in mean sea level and atmospheric conditions (as an indicator of waves in addition to surge), Perks et al (2023) assess projected future changes in coastal flooding according to the PPE using a weather-typing approach. Their emphasis is somewhat different to ours in that they are concerned with the ensemble signal of change (typically represented by the behaviour of the ensemble median), whereas we are more concerned with the largest change.…”

“…The expected annual damage in England and Wales alone due to coastal flooding is £0.5 billion and this figure is predicted to at least double over the 21st century in the absence of any adaptation (Hall et al 2006). Regional mean sea level (MSL) rise is expected to be the primary driver of the increased risk (Perks et al 2023, Howard et al 2019, Menéndez and Woodworth 2010. There could also be a secondary contribution from an increase in the level of the storm surges, relative to the mean sea level.…”