|TITLE||EXTRATROPICAL CYCLONES AND THE MEDITERRANEAN PRECIPITATION DECLINE IN THE CMIP5 MODELS FUTURE PROJECTIONS|
|AUTHORS||Giuseppe Zappa (1,2)|Matt Hawcroft (2)|Emily Black (1,2)|David Brayshaw (2)|Len Shaffrey (1,2)|
- NCAS-Climate, Reading, UK
- Department of meteorology, University of Reading, Reading, UK
|ABSTRACT||The Mediterranean region has been identified as a climate change hot spot due to a projected decline in precipitation and fresh water availability of potentially large socio-economic impact. However, the spread of the precipitation projections is large and having more confidence would benefit from relating these changes to the dynamical processes controlling the Mediterranean hydro--climate. Therefore, in this presentation the impact from changes in the behaviour of extratropical cyclones on the Mediterranean precipitation projections in winter will be explored by analysing present day and future scenario simulations from 17 CMIP5 climate models.
Extratropical cyclones in the CMIP5 models have been identified and tracked in time using an objective feature tracking algorithm applied to the 6 hourly relative vorticity at 850 hPa. Furthermore, a simple approach has been applied to identify the precipitation generated by each cyclone. This allows us to decompose the Mediterranean precipitation projections between a contribution due to future changes in the number of cyclones and a contribution due to changes in the precipitation intensity generated by each cyclone. Consistently with previous studies, we find that the overall Mediterranean precipitation decline is related to a reduction in the number of Mediterranean cyclones. However, the contribution from changes in the precipitation intensity of cyclones is also found to be important and to have local impacts comparable to those from the reduction in number. In particular, the North Mediterranean and the East Mediterranean regions, where the changes in the precipitation intensity have opposite sign, will be analysed in detail. By exploring the CMIP5 multi model spread, the precipitation intensity response is found to be related to the future changes in the atmospheric specific humidity and in the dynamical intensity of cyclones. The sensitivity to model resolution and the implications of these findings when interpreting the Mediterranean precipitation projections will be finally discussed.|