Temporal evolution of surface humidity in Turkey: recent trends and the role of sea surface temperatures

Abstract

In this study, variability and trends of surface humidity, and its relationship with meteorological parameters and sea surface temperatures (SSTs) are investigated for Turkey. Daily relative humidity (RH) and calculated specific humidity (SH) values of the 92 stations, which are homogenously distributed over Turkey, were used for the period 1965-2018. Land surface temperature and precipitation values of the stations and areal-average SST values of the adjacent seas, which are derived from NOAA High Resolution daily mean SST data, were used to find the impacts of physical mechanisms on the increasing or decreasing humidity values. RH values in the stations generally tend to decrease in all seasons, with the largest decrease are found in Mediterranean Region (MeR) during fall with 1.20% per decade, which implies a total decrease of 6.5% during the analysis period. Winter temperature and precipitation records in western/southern stations of Turkey are positively correlated with their RH values due to the transfer of humidity from relatively warm Aegean/Mediterranean SSTs by westerly/southerly winds. In SH, all regions show increasing tendencies; however, highest increments are shown during summer and the increasing trend is higher in the northern regions (i.e., Marmara and Black Sea) when compared to southern areas. The role of SSTs on SH changes is more remarkable during spring than the other seasons. Highest positive SST-SH correlations (p < 0.05) were found in Black Sea (Aegean Sea) regions during spring, summer, fall, and winter seasons with the Pearson's correlation coefficients (r) of 0.83 (0.69), 0.80 (0.48), 0.78 (0.58), and 0.59 (0.49), respectively. Additionally, northerly and southerly dominant wind regimes of the Marmara Region (NW Turkey) enable receiving significant amount of moisture from western Black Sea and northern Aegean Sea in all seasons.