The influence of groundwater to future flood risk

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Flood risk is changing worldwide, associated with population and socioeconomic growth, and climate change. Lower catchments and estuaries are particularly vulnerable because land value is high and susceptible to flooding from compounding extremes: sea-levels, precipitation, river flows and groundwater. For the UK, these drivers of flooding are not well-resolved spatio-temporally and their interactions are often poorly understood. Groundwater and soil moisture conditions prior to rainfall have been shown to be important components of flooding (MacDonald et al. 2008). Whilst researchers have investigated seasonal and spatial changes of groundwater and soil moisture nationally (Jackson et al 2015; Grillakis 2019), and changes on runoff generation locally, how these changes will affect flooding across the UK has yet to be investigated (Woldemeskel and Sharma 2016; Ascott et al. 2017). This PhD, therefore, aims to investigate:Where does groundwater contribute to flooding in the UK? What antecedent weather conditions exacerbate flooding, such as back-to-back storms?Can droughts or heatwaves contribute to flood resilience? How will flood risk change in a warming and more seasonal climate?We hypothesise that UK-catchments with high groundwater contributions will see reduced flooding in future summers, but increased in winters - and acknowledgement of antecedent weather conditions can improve flooding forecasts. Heatwaves above 30C are rare in the UK but expected to occur up to four times every summer by the end of the century, causing significant decreases in groundwater levels and soil moisture, but also causing intense downpours. Winters on the other hand will be up to a third wetter than presently, with uncertain effects of changing storm behaviour on groundwater. This PhD will apply these newly-released climate projections to coupled catchment-groundwater-marine models of contrasting UK-catchments with high groundwater contributions - the outcomes of which will have important implications for disaster emergency response, flood-risk management, catchment spatial-planning and ecosystem resilience.