Uncertainty and sensitivity of coastal flood risk estimates across the Solent, UK from 1920 to 2100

This thesis develops a methodology to understand the influence of environmental and socioeconomic factors on the past, present and future evolution of coastal flood risk on a regional level. The Solent, in the south of England, is selected as a case study region as it encompasses a variety of natural and urban coastal environments along its length, creating the opportunity to transfer the knowledge acquired and the methods developed to other areas in the UK and more widely. The richness of data and previous assessments for this region allow for a better understanding of the coastal processes, leading to more accurate assessments. The overreaching aim of this PhD study is to quantify the influence that each component of the Source-Pathway-Receptor-Consequence conceptual framework has on past, present and future coastal flood risk levels. The analysis uses a 2D inundation model coupled with improved population distributions to determine the risk of coastal flooding using the number of people threatened as the indicator. The uncertainty is assessed using a combination of scenarios and a variance-based sensitivity assessment. Three objectives are defined to assist in the completion of the aim. The first objective is to assess how coastal flood risk has evolved at the Solent between 1920 and 2000. Population growth was the primary driver of coastal flood risk during the 20th century, followed by a small contribution of sea-level rise, but defence improvement after 1940 slowed the rise in risk for some areas (e.g. Portsmouth). The second objective is to estimate the present-day risk of coastal flooding and quantify its sources of uncertainty. The average estimate is a risk of 1,480 people/year, equivalent to £145 million/year in 2020. The biggest uncertainties are given by the presence/absence and height of flood defences, but the height of extreme sea levels creates the largest variability for present-day coastal flood risk. The third objective is to determine how coastal flood risk may evolve over the remainder of the 21st century, given future sea-level rise, population change, and plausible coastal management strategies. The magnitude of sea-level rise causes the biggest uncertainties, and it is the main driver of coastal flood risk, which reaches an average of 4,581 people/year by 2100. Furthermore, the scenarios of coastal management strategies will not be sufficient to mitigate all of the future effects of climate and population change on coastal flood risk at the Solent. Hence, improved protection or alternative adaptive approaches would be prudent. The approach, methods developed, and learnings of this thesis can be transferred to other regions that follow a similar evolution to that of the Solent and can help steer their coastal management strategies