CReDo report 2: Generating Flood Data

Climate change will bring far reaching consequences across many aspects of society, including our health, prosperity and future security. The latest climate projections from the UK Met Office indicate that we will experience warmer, wetter winters and hotter, drier summers, together with an increase in the frequency and intensity of extremes. Substantial increases in hourly precipitation extremes are expected, with the frequency of days with hourly rainfall > 30 mm/h almost doubling by the 2070s. The increase in short, intense, rainfall events may be expected to manifest in flooding which can cause serious threats to society and the economy.

This report provides details of how flood data was generated within the CReDO project. A summary of different types of flooding are considered (river, coastal, surface water) together with an outline of standard industry approaches and requirements to quantifying probabilities of occurrence. We provide a summary of the information available within the UKCP18 projections, and how this can be used for assessing changes in precipitation under climate change scenarios. This includes the UKCP18 local projections, consisting of hourly data at a 2.2km resolution for 12 simulations from a convection-permitting model, with a bias correction applied, and the probabilistic extremes dataset (PPCE), with discussion of what information these products can and cannot provide.

Information on the risk of river and tidal flooding in the study region is provided from Environment Agency models. UKCP18 does not provide direct information on flooding, and the flood model HiPIMS was used to convert precipitation to surface water flooding. For generating storm events, FEH methodology was used, in combination with uplifts from different sources to represent the effects of climate change, and a discussion of how UKCP18 products may augment this approach, given appropriate consideration of the challenges in using this for decision making.

Using HiPIMS allowed the provision of multiple surface water flooding scenarios for different storm lengths, return periods (1 in 100, 1 in 1000 year events) and climate change scenarios, giving spatio-temporal maps of flood depth over time, in a form that can be used to assess the vulnerability of assets and consider how changes in the climate will affect the likelihood, and extent, of flooding in the future.

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