CReDo technical report 2: Generating Flood Data

Summary

Climate change will modify the frequency and magnitude of many extreme weather events. In the UK, flooding is expected to increase due to wetter winters and more intensive summer convective storms. In addition, sea level rise will threaten low-lying areas, overall posing a risk to communities, infrastructure and the delivery of services to society.

For the development of the CReDo connected digital twin, the processing, integration and interrogation of appropriate flood hazard information was required alongside asset data to test the ability of the system-of-systems to cope under a range of future flood scenarios. This report includes a list of open-source flood data to enable a rapid screening of the risk of a portfolio of assets. It also presents standard industry approaches to evaluate the extent and magnitude of flooding in the UK by a combination of hydrological and hydraulic models. Guidance and process for incorporating the impact of climate change into these evaluations is explained too.

Flooding can occur from a variety of sources, and two of them, the sea and direct rainfall, were investigated in detail given their relevance for the CReDo study area. Environment Agency coastal flood mapping was obtained and applied in the analysis. It considered the risk of flooding due to storm surge and waver overtopping exacerbated with sea level rise. The Environment Agency also provided fluvial (river) flood maps and models, which confirmed that river floods would be contained within flood defences even for climate change scenarios in the area under study. Information of this sort is held by the regulator nationwide and can be accessed upon request, constituting a desirable starting point of any detailed flood investigation. However, the risk of pluvial (surface water) flooding associated with intense direct rainfall onto the study area was missing, and modelling with HiPIMS (a hydrodynamic flood model) undertaken for a range of climate change projections for its characterisation. The model was able to combine the topography and land cover of the area with a set of pluvial, fluvial and tidal boundary conditions to represent overland flow in two dimensions.

Understanding the impact of climate change on flood hazard requires an estimation of changes in weather extremes, which can be derived using a range of climate models developed at a global, regional or local scale for a suite of scenarios representing various levels of global warming. UKCP18 is the most up to date set of climate projections available in the UK, which can be applied to flood models to establish changes in the likelihood and intensity (i.e. flood depth) of flooding at an asset level. In CReDo this was achieved by adding a climate change allowance to uplift the selected pluvial and fluvial extreme events. The standard industry approach is to adopt the allowances prescribed by the regulator for a certain time horizon and location. However, in CReDo, UKCP18 local projections for the high emission scenario were consulted to establish changes in the intensity of convective storms, and the probabilistic projections of extremes were used to examine the full range of uncertainty in emissions and climate models.

Although in this first phase of development the impact of climate change on a single extreme flood event has been used to demonstrate the future risk to assets, the long-term objective of CReDo is to expand the hazard information to include a greater number of events and additional risks (e.g. heat waves), so that the resilience of the system can be tested in a dynamic way. This will enable future work to quantify the impact on the level or service and to identify the critical assets contributing to it. Having a single platform for the processing, running and interrogation of climate, flood and asset data conjunctively is key for a realistic representation of the system operation, and this has been achieved in CReDo. This will help to prioritise adaptation actions to reduce risks to an acceptable level.