Tropical belt expansion and its impacts on climate variability in the Mediterranean from 1980 to 2022

Abstract. The Mediterranean region's climatic parameters are undergoing substantial changes driven by climate change and tropical belt expansion. This paper explores the long-term variability of climatic parameters over the Mediterranean region and their relationship with tropical belt expansion by employing observational and reanalysis data from January 1980 to December 2022 through multiple approaches including correlation, linear regression, singular value decomposition (SVD), wavelet coherence (WTC), and principal component analysis (PCA). The lapse rate tropopause height (LRT-H) exhibits upward trends of approximately 80.58 m/dec. Concurrently, the tropical belt shows poleward expansion of approximately 0.14 °/dec and 0.27 °/dec from both applied methods. The tropical edge latitudes (TELs) of both applied approaches are in phase and have a strong positive correlation with LRT-H, surface temperature, and tropospheric temperature while being of strong negative correlation and out of phase with precipitation. However, there is no substantial correlation for the Standardized Precipitation Evapotranspiration Index (SPEI) with TELs or other climatic parameters. The results of SVD analysis depict that the surface temperature and lower tropospheric temperature (TRP-1) have evident coupling with the TELs in the eastern Mediterranean. Furthermore, surface temperature and TRP-1 have significant increasing trends, which are abundant in the eastern and northern Mediterranean. On the other hand, both precipitation and SPEI exhibit downward trends. Over the Mediterranean, an apparent spatial and temporal variation of climatic parameters is observed. The results confirm the linkage between climatic parameters' variability, coherence, and covariability with the TELs variability patterns over the study area, especially in the eastern Mediterranean region.