M. Armon1, F. Marra2, D. Rostkier-Edelstein1,3, C. Garfinkel1, O. Adam1, U. Dayan4, Y. Enzel1, E. Morin1

1 The Hebrew University of Jerusalem, Fredy and Nadine Herrmann Institute of Earth Sciences, Jerusalem, Israel
2 National Research Council of Italy, Institute of Atmospheric Sciences and Climate, CNR-ISAC, Bologna 40129, Italy
3 IIBR, Department of Applied Mathematics, Environmental Sciences Division, Ness-Ziona 7410001, Israel
4 The Hebrew University of Jerusalem

Heavy precipitation events (HPEs) in the eastern Mediterranean trigger natural hazards, such as flash floods and urban flooding. However, they also supply critical amounts of fresh water to this desert-bounded region. The impact of global warming on such events is thus vital to the inhabitants of the region. Climate change impact on precipitation is no longer considered only as “wet gets wetter, dry gets drier”, but rather as a complex interaction of multiple factors acting concurrently, which is hard to assess using global climate models. HPEs are poorly represented in such models, leading to large uncertainty in their sensitivity to climate change. Is total rainfall in HPEs decreasing, as projected for the mean annual rainfall? Are short duration rain rates decreasing, or rather increasing as expected from higher atmospheric moisture contents? Is the area of storm getting larger or smaller?

To answer these questions, we have identified 41 historical HPEs from a long weather radar record and simulated them using a high resolution (1 km) convection-permitting WRF model under two different “storylines”. The first storyline is the historic scenario, for which simulations were validated with radar data. These results served as a control group for the second storyline, which is the RCP 8.5 scenario. Through this coupled set of simulations, also known as the ‘pseudo global warming’ (PGW) methodology, we can provide plausible future consequences of climate change on precipitation during HPEs.

Our results indicate that HPEs in the future may become much drier (-30% event-based average). They are also spatiotemporally more “concentrated” with shorter durations (-9%), reduced rainy area (-40%), but higher short-duration (10-min) rain rates (+15%). Given the high impact of HPEs on water resources and floods in the area, these results foreshadow the future of the region’s population, and requires action by policymakers.