Climate Change and Precipitation Extremes in Regional Climate Models
Hayley J. Fowler1, Marie Ekstrom2, Stephen Blenkinsop1, Elisabeth Kendon3, Mari Jones
1School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, United Kingdom; 2CSIRO Land and Water, CSIRO, Canberra, ACT, Australia; 3Met Office Hadley Centre, Exeter, United Kingdom

There is currently a trend towards increased precipitation and enhanced variability in the high latitudes of the northern Hemisphere, particularly in winter, and observational analyses suggest significant positive trends in daily rainfall intensities over the past decade. This change is physically consistent with warmer air being able to hold more moisture – General Circulation Models (GCMs) and satellite observations both indicate that the total amount of water in the atmosphere will increase at a rate of 7% per °C of surface warming – causing comparable rises in heavy precipitation events driven by moisture convergence.

Regional Climate Models (RCMs) simulate the magnitude and spatial pattern of observed daily extreme rainfall events more reliably than GCMs but still underestimate extreme rainfall in relation to observations. All RCMs have deficiencies in their representation of the magnitude and spatial variability of daily rainfall extremes. Though boundary forcing has the greatest impact on the magnitude of extremes in RCM simulations, changes in RCM specific formulations also lead to local-scale differences in biases and response to forcing. Recent research also shows that RCM simulation of extreme rainfall is better for long (e.g. 5 to 10 days) rather than short duration events and is best for the winter season when extreme rainfall is mostly associated with synoptic and mesoscale precipitation structures. Simulation of extreme rainfall is particularly poor in summer when convection dominates.

This presentation will evaluate the ability of RCMs to represent extreme precipitation processes and then present a new NERC-funded project that will investigate model deficiencies in the simulation of extreme rainfall. This will, for the first time, run a high resolution (1.5km) regional climate model over the UK to investigate the effect of model resolution on the simulation of extreme precipitation and produce new estimates of future change to convective extremes for pluvial flood risk.

Keywords: Downscaling; Regional Climate Models; Extremes; Precipitation

Biography: Dr. Hayley Fowler is Reader in Climate Change Impacts in the School of Civil Engineering and Geosciences at Newcastle University. Her NERC Fellowship (from 2006-2010) examined the links between atmospheric circulation patterns, extreme rainfall and flooding in the UK. She has more than 10 years experience in analysing the impacts of climate change and variability on hydrological systems, climate model outputs and recent trends in extremes and has developed specialised downscaling methodologies for these. She has published over 40 ISI-cited journal articles since 2000 and won £1.6M of funding as PI and £1.7M of funding as Co-I since 2004. One of her most exciting current projects, with the UK Met Office Hadley Centre, is running high-resolution regional climate models (at 1.5km resolution) over the UK to resolve convective rainfall processes and produce better future estimates for pluvial flooding.