Interpreting Century-Scale Changes in Southern North Sea Storm Surge Climate Derived from Coupled Model Simulations

Abstract

This paper describes numerical experiments using a climate-storm surge simulation system for the coast of the United Kingdom, with a particular focus on the southern North Sea and the Thames estuary in southeastern England.Time series of surges simulated in the southern North Sea by a surge model driven by atmospheric data from a regional climate model and surges simulated by the same surge model driven by atmospheric data from a global climate model are compared. A strong correspondence is demonstrated, and a linear scaling factor relating them is derived. This factor varies slowly with location. Around the Thames estuary, extreme surges are compared in the same way, and the linear scaling factor for the extremes is found to be similar to that for the full time series. The authors therefore assert that in seeking significant trends in surge at this location using this model arrangement, the regional model downscaling stage could be avoided, if observations were used to establish a suitable scaling factor for each location.The influence of the tide-surge phase relationship is investigated, and extreme sea levels at the mouth of the River Thames from regional-model-driven simulations are compared to the extreme event of 1953. Although the simulated levels are slightly lower, they are found to be comparable given the observational uncertainty.The assumption that time-mean sea level changes can be added linearly to surge changes is investigated at this location for large changes in time-mean sea level. The authors find that the primary effect of such an increase is on the speed of propagation of tide and surge, supporting the case for a simple linear addition of mean and extreme sea level changes.

Sources of 21st century regional sea-level rise along the coast of northwest Europe

“…Nevertheless, previous studies (e.g. Sterl et al, 2009;Howard et al, 2010) have shown that it is reasonable to combine surge changes additively with mean sealevel change. Similarly Howard et al (2014) show that for their model IDSL and ADSL changes appear to be additive.…”

“…Howard et al, 2010;Sterl et al, 2009) that changes in storm surge contribution to sea level can be added linearly to mean sea-level change and so, following Lowe et al (2009), that is the approach we took in this study.…”

Projected Change—North Sea

“…As there is sufficient evidence that the changes in extreme water level due to changes in time-mean sea-level rise and changes in storminess combine approximately linearly (e.g. Kauker and Langenberg 2000;Lowe et al 2001;Howard et al 2010) over a sizeable range of future sea levels, it is insightful to consider the two components in isolation.…”

Tide–surge interactions and their effects on total sea levels in Irish coastal waters

“…van den Brink et al 2003, Sterl et al 2009) is that the surge residuals correlate with tides (when interactions exist). In contrast, skew surges do not exhibit such correlations (Howard et al 2010) and were, therefore, unsuitable for this study.…”

“…Horburgh and Wilson (2007) added that surges are significantly greater at low water than at high water. This interpretation was used by Howard et al (2010) to justify greater surge residuals close to low water in the Thames estuary. Surge amplification due to interactions is also sensitive to the shape and time profile of the surge such that amplification increases with decreasing surge duration (Prandle and Wolf 1978).…”