Sensitivity of Estuaries to Climate Hazards (SEARCH)

居住在英国河口附近的2000万人面临着复合洪水灾害的风险。最近发生在英国集水区和河口的洪水（2013年12月至2017年1月）由于巨浪降水时间的微妙变化，情况可能会更糟，尽管仍然造成了5亿英镑的巨大损失。河口社区尤其容易受到未来洪水风险变化的影响；海平面上升加上风暴潮高度的增加，以及降水和温度模式的变化，将对河流的行为产生深远的影响。SEARCH项目将通过开发一种评估英国河口气候洪水危害的新方法，直接解决这一重要问题。该方法将首次适用于不同时空尺度、不同集水区和河口类型的复合洪水事件。该方法可以准确地解析所有水文和海洋过程及其联合概率。它将评估UKCP18的气候预测如何缩小到洪水影响；因此，为EA、北威州和SEPA提供独特和关键的淹没和可能性数据，以确定最易受复合洪水影响的社区，并在事件响应期间有效管理其资源。重要的是，我们将展示复合洪水是如何发生的，以及不同的系统对气候变化的不同驱动因素有多敏感。全球海平面预计将在本世纪上升1米，对于像英国这样的一些地区，降水和温度分布可能会发生变化，风暴、热浪和干旱等极端事件会随着时间的改变而变得更加强烈和季节性。洪水强度的变化预计会影响危害和风险。然而，我们假设它们彼此之间的时间变化对洪水风险也至关重要。例如，由于影响土壤湿度和地下水流量的降水和温度的变化，河流事件的时间可能会发生变化。作为NERC项目CHEST概念的证明，研究人员建立了河口对潮汐-涌浪-河流事件联合作用的敏感性，根据相对于河口的集水区大小、河口形状以及相对于彼此的涌浪和河流事件的时间，隔离河口内风险增加的不同区域。因此，气候变化导致的洪水风险变化将是特定地点的，灾害驱动因素的相对作用在空间上是不同的。极端事件的长期变化往往是不可预见的，因为我们对综合系统的理解是不完整的。考虑到河口的高社会经济和环境价值，复合灾害的复杂性，驱动因素的预测变化，以及不受监管的土地利用管理，制定新的战略来减轻复合洪水，并开发改进的洪水保护风险评估工具是及时的。与英国洪水监管机构合作，SEARCH将利用UKCP18降水、温度、河流流量、风暴潮和海平面预测的过去和新的观测结果，应用于一个快速、经过测试和开源的水动力学-地下水模型来模拟洪水危害。我们将模拟14个系统，覆盖英国范围内的位置和河口。我们的结果是迫切需要的，因为确定洪水风险的概率方法已经过时了，因为它们不能捕捉非线性动态，也不包括未来的变化。这个为期两年的项目汇集了集水区到海岸环境科学领域的世界领先研究人员（与班戈大学和赫尔大学的PDRAs一起），以解决这个在计算上具有挑战性且研究不足的问题。在主要政策和行业合作伙伴的参与和支持下，该团队成功地合作，建立了洪水风险的新范例，并积累了大量数据。

Twenty million people living near UK estuaries are at risk from compound flooding hazards. Recent near-miss flooding in UK catchments and estuaries (Dec-2013, Jan-2017) could have been much worse with subtle changes in surge-precipitation timings, although still caused extensive damage costing £500M. Estuary communities are especially vulnerable to future changes in flood risk; via sea-level rise combined with increases in storm surge heights - and changing precipitation and temperature patterns that will have profound impacts on fluvial behaviour. The SEARCH project will address this important issue directly by developing a new method to evaluate climate flooding hazards in UK estuaries. For the first time this method will be fit-for-purpose for compound flooding events across different spatial and temporal scales, and for different catchment and estuary types. This method will accurately resolve all hydrological and marine processes and their joint-probabilities. It will evaluate how climate predictions from UKCP18 downscale to flooding impact; hence, providing unique and crucial inundation and likelihood data for the EA, NRW and SEPA to identify the most vulnerable communities to compound flooding and to manage their resources effectively during incidence response. Importantly, we will show how compound flooding occurs and how sensitive different systems are to the different drivers of climate change. Global sea levels are expected to rise up to 1 m this century and for some regions like the UK, precipitation and temperature distributions are likely to change, with extreme events such as storms, heatwaves and droughts becoming more intense and seasonal with altered timings. Changes in the intensity of flood drivers are expected to affect the hazard and risk. However, we hypothesise that changes in their timings relative to one another will also be vital for flood risk. For example, the timings of fluvial events will likely change due to changes in precipitation and temperature affecting soil moisture and groundwater flow. As a proof of concept in the NERC project CHEST, the investigators established the sensitivity of estuaries to tide-surge-fluvial events acting in combination, isolating distinct zones within estuaries of increased risk depending on catchment size relative to the estuary, estuary shape and the timing of surge and fluvial events relative to each other. Changes in flood risk due to climate change will therefore be site specific, with the relative roles of hazard drivers varying spatially. Long-term changes in extreme events are often unforeseeable because our understanding of the integrated system is incomplete. Considering the high socio-economic and environmental value of estuaries, the complexity of compound hazards, the projected changes in drivers, and unregulated landuse management, it is timely to develop new strategies for mitigating against compound flooding and to develop improved risk assessment tools for flood protection.Working with the UK regulators of flooding, SEARCH will use past and new observations with UKCP18 projections of precipitation, temperature, fluvial flows, storm surge and sea level applied to a fast, tested and open-source hydrodynamic-groundwater model to simulate flooding hazards. We will simulate 14 systems that cover the range of locations and estuaries within the UK. Our results are urgently needed, as probabilistic methods of determining flood risk are obsolete because they do not capture the non-linear dynamics and do not include future changes. This two year project brings together world-leading researchers in catchment-to-coast environmental science (with PDRAs at Bangor and Hull Universities) to tackle this computationally challenging and under-investigated issue. This team have worked together successfully, with the involvement and support of key policy and industrial partners, establishing a new paradigm in flood risk and accumulating a vast amount of data.