September 2008 Morpeth Flood addition - Performance of ensemble rainfall forecasts in relation to pluvial flooding impacts

在2007年发生大洪水之后，英国政府委托编写了一份报告(《皮特审查》)，阐述了应对这一问题所需采取的行动。该报告的一项关键建议是需要“改进对所有形式的洪水的模拟”。到目前为止，人们最关注的是开发河流洪水(河流洪水)的计算机模型，但相当大比例的洪水是由导致局部径流的降雨事件(洪水洪水)引起的。这些洪水事件很难预测，因为它们往往是局部高强度降雨(通常与对流风暴有关)，以及城市地区通过地下排水沟和陆地径流。大都会博物馆的新版本。该办公室的业务天气预报模式最近开发了高分辨率(1.5公里)，能够更准确地描述这些当地降雨事件，有可能用于支持更好的洪水预报。该提案旨在将新模型的产出用于9月6日的案例研究活动。2008年莫佩斯洪水影响了大约1000处房产。这一案例研究特别有价值，因为它是在以前的项目中根据公开来源的信息详细测量洪水动态的极少数事件之一，这使得能够详细重建不同的洪水来源，以便与洪水模型进行比较。来自1.5公里天气预报模式的详细降雨数据的质量。2008年Morpeth洪水事件将通过与雨量观测和英国目前使用的其他标准方法进行比较来进行评估，包括评估降雨量数据中的不确定性。然后，这些数据将被输入来自局部集水区的径流的水文模型，并用于模拟流入城镇的水量，以及洪水如何到达泛滥平原的不同区域，以便与这次事件的观测洪水水位进行比较。这一案例研究是第一次使用新的天气预报模型降雨预测包括不确定性的洪水模型，并将有助于支持英国各地从雨源建立洪水预测模型的发展。

Following the major floods in 2007, the UK Government commissioned a report (the Pitt Review) which formulated the actions needed to respond to this issue. A key recommendation of the report was the need for 'improved modelling of all forms of flooding'. Most attention so far has been paid to developing computer models of flooding from rivers (fluvial flooding), but a significant percentage of flooding is from rainfall events which lead to localised runoff (pluvial flooding). These flood events are difficult to predict as they are often have local high intensity rainfall (typically associated with convective storms) and runoff in urban areas through subsurface drains as well as overland. A new version of the Met. Office's operational weather forecast model has recently been developed with a high (1.5km) resolution that is capable of representing these local rainfall events more accurately, with the potential to be used to support better predictions of pluvial flooding. This proposal aims to use the outputs from the new model for the case study event of the 6th Sept. 2008 Morpeth flood that affected around 1,000 properties. This case study is particularly valuable, as it is one of the very few events for which the dynamics of the flooding have been measured in detail in a previous project from publicly-sourced information, which has allowed detailed reconstruction of the different sources of flooding for comparison against flood models. The quality of the detailed rainfall data from the 1.5km weather forecast model for the Sept. 2008 Morpeth flood event will be assessed through comparison with raingauge observations and other standard approaches currently used in the UK, including assessment of the uncertainty in the rainfall data. These data will then be fed into hydrological models of runoff from the localised catchment areas, and used to simulate the volumes of water flowing into the town, and how the floodwater reaches the different areas of the floodplain, allowing comparison against the observed flood levels for this event. This case study is the first to use the new weather forecast model rainfall predictions including uncertainty for flood modelling, and will help to support development of flood prediction modelling from pluvial sources across the UK.