EGU21-7258
https://doi.org/10.5194/egusphere-egu21-7258
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Unprecedented summertime daily rainfall across the UK

Chris Kent1, Nick Dunstone1, Simon Tucker1, Adam Scaife1,2, Elizabeth Kendon1, Simon Brown1, Doug Smith1, Shirley Greenwood3, and Lynsay McLean3
Chris Kent et al.
  • 1Met Office Hadley Centre, Exeter, UK
  • 2College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK
  • 3Environment Agency, UK

The UNSEEN (UNprecedented Simulated Extremes using ENsembles) method involves using a large ensemble of initialised climate model simulations to increase the sample size of rare events. In this work we extended UNSEEN to focus on intense summertime daily rainfall events. Specifically, plausible extreme rainfall scenarios were developed to help understand potential surface water flooding impacts, and ultimately better inform flood management and resilience across the UK. To help address modelling limitations a large ensemble of simulations from two climate models were used; an initialised 25km global model that uses parametrized convection, and a dynamically downscaled 2.2km model that uses explicit convection. Climate model fidelity was assessed using a regional pooling technique based on extreme value theory. Across much of the UK both models are indistinguishable from the observations in terms of the statistical characteristics which govern the magnitude of very rare return periods. The UNSEEN analysis provides new estimates of plausible extreme return levels (i.e. 1-in-1000 year) across the UK and can reduce uncertainty in the expected frequency of very rare events by 50-70% compared to estimates using observations alone. These results enable suitable observed rainfall profiles to be uplifted to plausible extreme return levels, which can then be used within regional hydrological models to stress test surface flooding scenarios. The annual chance of unprecedented daily rainfall events in the current climate is also quantified, and found to be up to 5% (1-in-20 year return level) for many grid cells across southern parts of the UK. Finally, a significant benefit of the UNSEEN approach over purely statistical emulators is the use of dynamical climate models which allow the large-scale dynamical drivers of extreme daily summertime rainfall to be assessed.

How to cite: Kent, C., Dunstone, N., Tucker, S., Scaife, A., Kendon, E., Brown, S., Smith, D., Greenwood, S., and McLean, L.: Unprecedented summertime daily rainfall across the UK, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7258, https://doi.org/10.5194/egusphere-egu21-7258, 2021.

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