High-Resolution Climate Simulations Over the Eastern Mediterranean Black Sea Region Using the Pseudo-Global Warming Method With a CMIP6 Ensemble

The strong drying expected in the Eastern Mediterranean with climate change could cause mass migration of people already living under water shortages. On the other hand, precipitation is expected to increase toward the region's north, particularly those along the interior of the eastern Black Sea coasts, which could worsen existing floods. However, this double-sided adverse phenomenon and its underlying reasons have been investigated by relatively low-resolution models in the Eastern Mediterranean Black Sea (EMBS) region, where orographic precipitation prevails. This study performs 4 km resolution Weather Research and Forecasting (WRF) model simulations with and without climate change signals retrieved from a CMIP6 GCM ensemble via pseudo-global-warming (PGW). The WRF simulations captured the large-scale dynamics affecting the EMBS fairly well: an anticyclonic low-level circulation and enhancing subsidence stem from anomalous ridge development over the central Mediterranean in winter (DJF), and a cyclonic low-level circulation and weakening subsidence rise from heat-low development over the Eastern Mediterranean in summer (JJA). The resulting picture of future warming and drying over the area generally supports the literature, although new insights emerge in anomalous precipitation increase, especially in the summer season over the Greater Caucasus and nearby regions. Most likely, the warmer-than-expected Caspian Sea induces a large increase in specific humidity and, thus, a large moisture source in the lower troposphere and an extension of the heat-low effect in the mid-troposphere. In addition, the high-resolution WRF simulations provide added value over the complex topography of the Caucasian Mountain range for new insights into this region. One of the most vulnerable parts of the Mediterranean climate change hotspot is the Eastern Mediterranean Black Sea (EMBS) region. The future climate change signal of the state-of-the-art CMIP6 GCM ensemble between 2071-2100 and 1985-2014 periods was retrieved for the region under the Shared Socioeconomic Pathway (SSP5-8.5). The signal was used to perturb ERA5 reanalysis data for the IPCC AR6 baseline period, 1995-2014, in the context of the pseudo-global warming (PGW) method. The Weather Research and Forecasting (WRF) model was used to obtain very high-resolution (4 km) climate data. According to the study, the future winters were as expected: anomalous ridge formation over southern Italy, resultant northeasterlies over the EMBS, the large-scale mid- and upper tropospheric subsidence, attenuation of the land-sea temperature contrast and finally, strong drying. The summers exhibit negative vertical pressure velocity changes, strengthening Etesians, and strong surface warming in line with the expectations of the literature. However, summers brought anomalous precipitation to the Greater Caucasus and nearby areas in our high-resolution WRF simulations. We think these new insights are primarily caused by the warmer-than-expected Caspian Sea stemming from the SST availability among the ensemble, a very convective environment for the region and better-resolved complex-orography-induced precipitation. The WRF-PGW simulations perfectly capture the low-level circulation change and warming/drying signals from CMIP6 for the EMBS in winter The WRF-PGW simulations show heat-low formation over the EMBS in summer, in line with the CMIP6 GCM ensemble The new insights appear in future summer precipitation increases over the Greater Caucasus and nearby regions