Spatiotemporal variability and underlying large-scale atmospheric mechanisms causing the change in the Black Sea surface temperature and associated extreme precipitation events in the northeastern of Turkiye

Abstract

Sea surface temperature (SST) has an important local and remote influence on global climate through the distribution and transport of heat and moisture. As a result of climate forcing, significant changes occur in the SSTs, which result in many natural disasters such as supercharged storms, higher wind speeds, heavier precipitation and flooding. This study investigates the spatiotemporal changes and underlying atmospheric mechanisms of the Black Sea (BLS) surface temperature. For this purpose, National Oceanicand Atmospheric Administration (NOAA) high-resolution SST data (0.25 degrees), which were verified with buoy observations, were used for the period 1982-2021. To investigate the circulation impacts, the relationship between North Atlantic Oscillation and East Atlantic/West Russia (EA/WR) phases and SSTs of the western BLS (WBLS) and eastern BLS (EBLS) was analysed. According to the results, SST values increased from 1.64 degrees C (in winter) to 2.52 degrees C (in summer) during the 40-year period. Significant SST increases are shown in the EBLS during the summer and fall months. Statistically significant negative correlations (p < 0.05) were found between EA/WR and winter (r = -0.57) and summer (r = -0.56) SSTs in the EBLS. During winter, surface high located in the eastern Anatolia causes southerly winds, which blows from the terrestrial areas to the EBLS and result in above-normal SST values. During summer (under negative EA/WR phases), the Azores high-pressure centre extends to the Balkan Peninsula and WBLS and as a consequence, a significant amount of moisture associated with high sea surface temperature (>27 degrees C, above-normal 2.0 degrees C) develops low-level moisture convergence. Proper synoptic conditions, strong instability conditions between the surface and upper levels, and orographic forcing enable the occurrence of convective cloud cells. The movement of these cells to the northeastern part of Turkiye by strong northwesterly winds causes extreme precipitation and associated flash-flood events in a limited area where land-sea interaction occurs (i.e., Artvin, Rize and Hopa provinces of Turkiye).