Over the past 60 years, both average daily precipitation intensity and extreme precipitation have increased in many regions1,2,3. Part of these changes, or even individual events4,5, have been attributed to anthropogenic warming6,7. Over the Black Sea and Mediterranean region, the potential for extreme summertime convective precipitation has grown8 alongside substantial sea surface temperature increase. A particularly devastating convective event experienced in that region was the July 2012 precipitation extreme near the Black Sea town of Krymsk9. Here we study the effect of sea surface temperature (SST) increase on convective extremes within the region, taking the Krymsk event as a showcase example. We carry out ensemble sensitivity simulations with a convection-permitting atmospheric model and show the crucial role of SST increase in the extremeness of the event. The enhancement of lower tropospheric instability due to the current warmer Black Sea allows deep convection to be triggered, increasing simulated precipitation by more than 300% relative to simulations with SSTs characteristic of the early 1980s. A highly nonlinear precipitation response to incremental SST increase suggests that the Black Sea has exceeded a regional threshold for the intensification of convective extremes. The physical mechanism we identify indicates that Black Sea and Mediterranean coastal regions may face abrupt amplifications of convective precipitation under continued SST increase, and illustrates the limitations of thermodynamical bounds for estimating the temperature scaling of convective extremes.
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The authors thank M. Akperov for assistance with analysis, A. Gavrikov for helpful comments about the simulation, and O. Bulygina for providing meteorological data from the All-Russian Research Institute of Hydrometeorological Information—World Data Centre. Simulations were carried out at the North-German Supercomputing Alliance (HLRN). This study was financially supported by the EUREX project of the Helmholtz Association (HRJRG-308) and partially supported by the Russian Ministry of Education and Science (contracts 14.B25.31.0026), the RF President grant (MK-3895.2014.5) and the Russian Foundation for Basic Research (grants 12-05-91323, 14-05-00518, 15-35-20962). Russian meteorological data were processed and supported by the Russian Science Foundation (grant 14-17-00700).