FUTURE-FLOOD: New estimates of evolving UK flood risk for improved climate resilience

最近席卷英国和欧洲的毁灭性洪水突显了让社会对洪水更具弹性的必要性。鉴于随着气候变化，洪灾预计将变得更加频繁和破坏性，这一需求更加迫切。然而，目前对英国和其他地方未来洪水风险的估计是不可靠的，因为它们通常基于分辨率较低的气候模型，无法捕捉导致洪水的短期极端降雨。它们也没有捕捉到降雨事件的空间范围和时间聚集性的关键变化，并忽略了改变降雨和河流流动模式的关键物理过程。未来洪水是一个雄心勃勃的项目，旨在促进我们对未来内陆洪水风险的了解，并在英国各地提供符合目的的新洪水估计。它将把国际上最先进的高分辨率气候预测与先进的洪水模拟能力结合起来。我们将开发一套新的100年连续气候预测，为英国每个2.2公里的网格框提供每小时的降雨量数据，为12个组合成员提供1981-2080年的数据。这就像启动了12个天气预报，每个预报运行了100年。这些预测(“UKCP Local”的延伸只适用于三个20年的时期)在空间和时间覆盖范围上都是独一无二的。它们将被用来对未来几年和几十年的降雨量变化有新的了解，包括时间聚集性、前兆条件和事件空间范围的变化。这些变化还不是很清楚，但很可能对洪水风险至关重要。100年的UKCP地方预测将被用于驱动水文和洪水模型，首次在英国范围内对复合洪水和河流洪水的频率和严重程度的变化提供完整的评估。UKCP将直接使用当地降雨数据，以便在模拟的河流流量和洪水水位中捕获降雨模式和强度分布的复杂变化。最近的一项试点研究(由项目组进行)表明，使用完整的UKCP当地时空变化降水场来驱动洪水模型，可能会导致对未来洪水风险的估计与基于简化隆起方法的当前指导中包含的完全不同。这项初步研究没有捕捉到复合效应，仅限于一个雨区(布里斯托尔)和两个河流集水区(Thet和Dyfi)，但证明了这里提议的全国范围研究的必要性。我们将把结果与使用标准方法和更粗分辨率的气候模式数据模拟的洪水进行比较，以评估现有洪水预报的可靠性。额外的洪水模型实验将使我们能够确定对洪水及其随时间变化的物理控制，包括降雨时空变异性变化的作用及其与地形的相互作用。这一理解将是确定从业人员在未来洪水风险评估中常用的改进抬升方法的关键。连续提供超过100年的洪水预测是向前迈出的重要一步，将使我们能够在气候变化的背景下解释个别观测到的洪水事件，并将结果转化为与特定政策相关的全球变暖水平的变化。我们将把新的洪灾风险信息与风险暴露和脆弱性估计结合起来，以评估洪灾风险(例如，财产被淹、关键基础设施受损、货币损失)。这一估计将包括对社会经济变化的预测。我们将展示这些新信息在国家范围内的决策中的使用。我们还将与城市决策者共同开发一个当地规模的演示器(最初是为布里斯托尔)，将新的洪水信息带到提高城市复原力、评估适应性行动的范围和好处方面。

Recent devastating floods across the UK and Europe have highlighted the need to make society more resilient to flooding. This need is even more urgent given that flooding is predicted to become more frequent and destructive with climate change. However, current estimates of future flood risk in the UK and elsewhere are unreliable as they are typically based on coarse resolution climate models, which are unable to capture the short-duration rainfall extremes responsible for flooding. They also do not capture critical changes in the spatial extent and temporal clustering of rainfall events and neglect key physical processes in changing rainfall and river flow patterns. FUTURE-FLOOD is an ambitious project to advance our understanding of future inland flood risk and provide new flood estimates across the UK that are fit for purpose. It will bring together internationally state-of-the-art high resolution climate projections with advanced flood modelling capability. We will exploit a new set of continuous 100yr climate projections that provide rainfall data hour by hour, for every 2.2km grid box across the UK, for 1981-2080 for twelve ensemble members. This is like starting twelve weather forecasts and running each for 100yrs. These projections (an extension of "UKCP Local" only available for three 20yr periods) are unique in their spatial and temporal coverage. They will be exploited to gain new understanding of changes in rainfall over the coming years and decades, including changes in temporal clustering, antecedent conditions and spatial extent of events. Such changes are not well understood but are likely to be critically important for flood risk.The 100yr UKCP Local projections will be used to drive hydrological and flood models, providing a complete UK-wide assessment of changes in the frequency and severity of compound pluvial and fluvial flooding for the first time. UKCP Local rainfall data will be used directly such that complex changes to rainfall patterns and intensity distributions are captured in the simulated river flows and flood levels. A recent pilot study (carried out by the project team) showed that using the full UKCP Local space-time varying precipitation fields to drive flood models can lead to radically different estimates of future flood risks to those contained in current guidance based on simplified uplift methods. This pilot study did not capture compound effects and was limited to only one pluvial site (Bristol) and two fluvial catchments (Thet and Dyfi) but demonstrated the need for the national-scale study proposed here. We will compare results with flooding simulated using standard approaches and coarser resolution climate model data, assessing the reliability of existing flood predictions. Additional flood modelling experiments will allow us to identify the physical controls on flooding and its change through time, including the role of changes in the space-time variability of rainfall and its interactions with the landscape. This understanding will be key to identifying improved uplift approaches commonly used by practitioners for future flood risk assessment.Providing flood projections continuously over 100yrs is a major step forward and will enable us to interpret individual observed flood events in the context of climate change and translate results to changes for specific policy-relevant global warming levels. We will combine the new flood hazard information with estimates of exposure and vulnerability to estimate flood risk (e.g. properties flooded, damage to critical infrastructure, monetary loss). This estimation will include projections of socio-economic change. We will demonstrate the use of this new information in decision-making at national scale. We will also co-develop a local-scale demonstrator (initially for Bristol) with city decision-makers to take the new flood information through to improving city resilience, assessing the scope for and benefits of adaptive action.