Towards modeling the regional rainfall changes over Iran due to the climate forcing of the past 6000 years

Abstract

We present a climate modeling approach to reproduce the rainfall patterns over Iran due to the climatic forcings during the past 6000 years. The selected periods are simulated using a spatially high-resolved atmosphere General Circulation Model (GCM). Our results show that the winter rainfall patterns over Iran have changed due to the changes in solar insolation with a wetter condition starting around 3 ka BP and reaching its maximum during the Medieval Climate Anomaly ca. 1 ka BP. The rainfall variability can be explained by the changes in atmospheric conditions as a result of changing incoming solar irradiance based on the Milankovitch theory. A shift in the Earth's energy budget leads to the modulation of the West Asian Subtropical Westerly Jet (WASWJ). The investigations support the hypothesis that during the Holocene a northward shift in the WASWJ contributes to the less cyclonic activities over Iran. This brings less moisture into the region during the winter.