Intensification of Tropical-Like Cyclones Over the Black Sea In the Future Climate: Blackcane Simulations

It is observed that extreme weather events, particularly short-duration high-precipitation events, have been intensifying in recent years over the Mediterranean and Black Sea regions under the influence of warmer sea surface temperature. On 10–13 August 2021 over the northeastern Black Sea region, an extreme precipitation event occurred in association with a low-pressure system where the sea surface temperature anomalies were 3°C higher.

In order to improve our understanding of how such late-summer low-pressure systems may evolve under future climate conditions, we applied the Pseudo-Global Warming (PGW) method using the Weather Research and Forecasting model at convection-permitting resolution. Counterfactual future scenarios were generated by defining climate-change-deltas which is future periods (2025-2049, 2050-2074, 2075-2099) minus historical period (1990-2014). These climate-change-deltas derived from CMIP6 models under SSP2–4.5, SSP3–7.0, and SSP5–8.5 scenarios were added to ERA5 initial and boundary conditions.

The simulations indicate that future warming can substantially intensify the dynamical structure of the event. While the control simulation which is driven by ERA5 represents the system as a relatively weak low-pressure disturbance, the future PGW experiments produce a much deeper and more organized cyclone. In several simulations, the system develops tropical-like characteristics over the Black Sea which we call blackcane, with a warm-core structure, enhanced low-level convergence, and stronger vertical motion. Cyclone phase-space analysis confirms this structural transition, indicating that future warming promotes the development of a more symmetric warm-core cyclone with stronger blackcane characteristics. These dynamical changes are accompanied by a remarkable increase in near-surface wind speed. In the control simulation, maximum wind speed remains below severe-cyclone intensity, reaching 89 km/h. In the future-climate simulations, maximum wind speeds increase dramatically, reaching 132–181 km/h in the strongest forcing experiments. Minimum sea-level pressure also decreases to below 975 hPa, reaching about 969–970 hPa.

These findings suggest that warmer sea surface temperature and future atmospheric warming may not only enhance extreme precipitation but also support the development of deeper, stronger, and more hazardous blackcane cyclone.

The numerical calculations reported in this thesis were partially performed using high-performance computing resources provided by TÜBİTAK ULAKBİM High Performance and Grid Computing Center (TRUBA) and Sigma2, the National Infrastructure for High-Performance Computing and Data Storage in Norway.