Compound flooding from tropical cyclone-induced sea surge and precipitation in Sri Lanka (C-FLOOD)

斯里兰卡北部和东部的沿海社区面临着与季节性气旋相关的风暴潮造成的沿海洪水的风险比该国其他地区大得多。这些风暴潮基本上是由天气系统造成的海平面局部升高，随后淹没了陆地。风暴潮是由以下几种因素的组合引起的：（1）低气压"抬升"海面（气压潮汐）;（2）吹过海面的风的摩擦阻力导致水面倾斜（风应力）;（3）破碎的波浪将其动量转移到水柱中（波浪建立）。Wijetunge教授与灾害管理中心合作制作了灾害地图，以显示斯里兰卡海岸线周围预计的风暴潮洪水。这些危险图所依据的计算机模型仅限于描述气压潮汐和风应力。随后的理解进步意味着现在可以包括波浪设置。这样做至关重要，因为波浪设置效应可能占某些地区激增的40%，即一些社区可能面临比迄今为止意识到的更严重的风险。然而，情况可能比这更糟，因为科学家们开始了解风暴潮与印度洋地区几乎总是伴随着飓风的严重降雨事件的相互作用。这种所谓的复合洪水的机制是，由于暴雨导致的河水上涨，由于风暴潮进入内陆而无法有效地排入大海。为了防止西部发生洪水事件，我们熟悉防洪结构;斯里兰卡没有这种硬工程结构。然而，它们确实具有自然保护特征，如红树林和盐沼。自2004年毁灭性的节礼日海啸以来，特别是红树林的潜在好处受到了一些关注，尽管在正式的沿海计划中有意实施仍处于起步阶段。泰勒教授最近获得全球挑战研究基金（Global Challenge Research Fund）的资助，研究设计规范如何将其影响纳入其中。在此背景下，C-FLOOD项目将基于最先进的计算机建模，考虑所有风暴潮成分和降雨影响，制作新一代复合洪水灾害地图。它还将考虑各种气候变化情景，这些情景将因预测的海平面上升而影响洪水。这将由SL Peradeniya大学的Wijetunge教授和东伦敦大学的Jayaratne博士利用他们的相关专业知识完成。此外，通过在普利茅斯大学海岸实验室进行实验，自然植被的保护作用将被纳入建模和地图中。这将由Raby博士（普利茅斯）和Taylor教授（西澳大利亚大学）进行。C-FLOOD项目将侧重于三个社区，这些社区因其地理位置和贫困程度（与过去的军事冲突有关）而被认为是最脆弱的。项目小组将与社区成员以及地方和区域领导人/行政人员合作，最大限度地发挥新的灾害地图的效益和利用率。个别的局部危险也将被捕捉在社区的综合多危险地图。来自东伦敦大学的Kitagawa博士和海岸保护和海岸资源管理部的Ranawaka先生过去都有此类活动的经验，他们将监督这些关键方面。最终的结果将是改进洪水淹没的预测，并与选定的社区合作，从而提高对复合洪水的抵御能力。灾害地图制作技术和减轻洪水影响的方法随后可在其他脆弱社区实施。

Coastal communities in the north and east of Sri Lanka (SL) face significantly greater risk of coastal flooding from storm surges associated with seasonal cyclones than those in the rest of the country. These storm surges are essentially local elevations in sea level caused by the weather system which subsequently inundate the land. Storm surges are caused by a combination of: (1) low atmospheric pressure 'lifting' the sea surface (barometric tide) (2) frictional drag of the wind blowing over the sea causing a slope in the water surface (wind stress) and (3) breaking waves transferring their momentum into the water column (wave setup). Hazard maps, to indicate predicted storm surge inundations around the Sri Lankan coastline, were produced by Prof Wijetunge in association with the Disaster Management Centre. The computer models on which these hazard maps were based, were limited to describing only the barometric tide and the wind stress. Subsequent advancements in understanding mean that wave setup can now be included. It is critical to do so, because the wave setup effect may contribute 40% of the surge in some locations i.e. some communities may face a more grave risk than hitherto realised. The situation is potentially much worse than this however, as scientists are beginning to understand the interaction of storm surges with severe rainfall events which almost always accompany the cyclones in the Indian Ocean region. The mechanism for this so-called compound flooding is that rivers swollen from heavy rainfall are prevented from effectively discharging to the sea due to storm surges coming inland.To protect against flooding events in the west we are familiar with flood defence structures; Sri Lanka has no such hard-engineered structures. However, they do have natural protective features such as mangrove forests and salt marshes. The potential benefits of mangroves in particular have received some attention since the devastating Boxing Day tsunami of 2004, though the intentional implementation in formal coastal schemes is still in its infancy. Prof Taylor recently received funding from the Global Challenge Research Fund to investigate how design codes might incorporate their effects.Against this backdrop, the C-FLOOD project will produce a new generation of compound flood hazard maps, based upon state-of-the-art computer modelling that will consider all the storm surge components and the rainfall effect. It will also consider a variety of climate change scenarios which will influence flooding due to predicted rising sea levels. This will be done by Prof Wijetunge at the University of Peradeniya in SL, and Dr Jayaratne at the University of East London, with their related expertise. Furthermore, the protective effects of the natural vegetation will be included in the modelling and maps, by conducting experiments at the University of Plymouth's COAST Laboratory. This will be undertaken by Dr Raby (Plymouth) and Prof. Taylor (University of Western Australia). The C-FLOOD project will focus on three communities that are deemed most vulnerable due to their geography and levels of poverty (associated with the past military conflict). The project team will work with community members in addition to local and regional leaders/administrators to maximise the benefits and uptake of the new hazard maps. Individual localised hazards will also be captured in comprehensive multi-hazard maps for the communities. Dr Kitagawa from the University of East London and Mr Ranawaka of the Coast Conservation & Coastal Resource Management Department have past experience of such activities and will be overseeing these critical aspects.The final outcome will be improved predictions of flooding inundation, with engagement of the selected communities, leading to improved resilience to compound flooding. The hazard map production techniques and flood impact mitigation methods could then be implemented across other vulnerable communities.