The influence of groundwater to future flood risk

洪水风险正在全球范围内发生变化，与人口和社会经济增长以及气候变化有关。较低的集水区和河口尤其脆弱，因为土地价值高，容易受到海平面、降水、河流流量和地下水等复杂极端因素的洪水影响。对于英国来说，这些洪水驱动因素在时空上还没有得到很好的解决，它们之间的相互作用通常也没有得到很好的理解。降雨前的地下水和土壤水分状况已被证明是洪水的重要组成部分（MacDonald et al. 2008）。虽然研究人员已经在全国范围内调查了地下水和土壤湿度的季节和空间变化（Jackson等人2015；Grillakis 2019），以及当地产流的变化，但这些变化将如何影响整个英国的洪水尚未得到调查（Woldemeskel和Sharma 2016； Ascott等人2017）。因此，这位博士的目的是调查：地下水在英国的哪些地方导致了洪水？之前的什么天气条件会加剧洪水，比如连续的风暴？干旱或热浪能提高抗洪能力吗？在气候变暖和季节性更强的情况下，洪水风险将如何变化？我们假设，地下水贡献高的英国集水区在未来的夏季洪水会减少，但在冬季会增加——并且承认之前的天气条件可以改善洪水预报。30摄氏度以上的热浪在英国很少见，但预计到本世纪末，每年夏天将出现多达四次，导致地下水位和土壤湿度显著下降，但也会导致强降雨。另一方面，冬季的降雨量将比现在多出三分之一，而不断变化的风暴行为对地下水的影响尚不确定。本博士将把这些新发布的气候预测应用于集水区-地下水-海洋耦合模型，对比地下水贡献高的英国集水区，其结果将对灾害应急响应、洪水风险管理、集水区空间规划和生态系统恢复能力产生重要影响。

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.