A new paradigm for urban flood design storms accounting for variability in space and time under climate change

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The extent and severity of the damage caused by urban floods is a product of both the intensity and duration of the rainfall (variable in space and time) and its interaction with the complex flowpaths of a city, on the surface and below ground (drainage network). Resilient design of urban drainage under climate change is currently blocked by the lack of a realistic design storm methodology. Conventionally, Intensity-Duration-Frequency (IDF) curves based on point rainfall measurements are used in design and such use of single events with standard profiles in time and uniform in space is widely recognised to be unrealistic, as individual storm events in large urban areas show great variation in key properties, and their spatial distribution and sequencing can interact strongly with critical pathways and vulnerable areas in cities. The main objective of this proposed PhD research is therefore to analyse precipitation extremes in a changing climate using high resolution climate model outputs, advanced stochastic modelling methodologies and the CityCAT urban flood modelling system. This project will develop new ensemble descriptions of storms to be used in multiple hydrodynamic simulations of cities with different characteristics. The new methodology will be developed using real cities, as well as synthetic networks in order to provide a wider range of situations to demonstrate robust design optimisation. The resulting framework will be widely applicable and of interest to water utilities, lead local flood authorities and consultancies. In this work, high-resolution climate model outputs will be used in order to create a methodology for deriving realistic storm events for a range of cities under climate change. These events then are going to be used to optimize urban drainage design. This will be achieved by creating a framework to run and analyse hydrodynamic simulations from the fully coupled (surface and surface drainage network) hydrodynamic model CityCat. Possible blue-green interventions also be explored.