Thermodynamic Drivers of Precipitation Variability over the Arabian Peninsula

We apply a Lagrangian-based moisture back trajectory method on two reanalysis datasets to determine the moisture sources for precipitation over the Arabian Peninsula, defined as land on the Asian Continent to the south of the Turkish border and west of Iran. We split the area from 65°W west to 120°E and 30°S to 60°N into twelve separate regions based on climate characteristics and apply the algorithm to determine the sources of moisture. Our results indicate a North to South spatial heterogeneity in the dominant moisture sources. In the northern parts of the Peninsula, moisture for precipitation is mostly sourced from European land and major water bodies including the Mediterranean and Caspian Seas. In the central region of the Peninsula, moisture from the western Indian Ocean and Atlantic Ocean play an important role. Central and Southern Saudi Arabia along with the Gulf states primarily receive moisture from the western Indian Ocean, in addition to some contribution from the eastern African continent that exhibits monsoonal climate during the Arabian Peninsulas wet season from November to April. We find a significant drying trend over parts of the Peninsula. While not all trends are explainable in terms of moisture source variability, decreasing trends over the southern region are attributable to a reduction in moisture advection from the African continent. Overall, this study establishes a new understanding towards the thermodynamic structure of climate over Arabian Peninsula and should help in the quantification of processes of precipitation variability and change over this region.