Decadal Change of Iran's Precipitation Regime

Abstract

In the current study, the decadal changes in Iran's precipitation regimes (PRs) were investigated by adopting Iran's precipitation dataset and using the precipitation index (PI). Our finding revealed that significant decadal variation occurred in the PI, which led to different spatial patterns during under investigation decades. From the 1st to last decades under study, the area decreased in the regions with equal monthly distribution of precipitation (ED). The regions with a relatively equal monthly concentration of precipitation (RED) presented a sharp decreasing trend in the first 3 decades and a slight increase in the last decade. The irregular distribution of precipitation (ID) in most of the decades covered an area above the long-term average. The highly irregular distribution of precipitation (HID) covered a small area of Iran's territory on the southern coasts. Nevertheless, its decadal variation, particularly in the first 3 decades, was relatively noticeable. The decadal variability of the number and tracks of cyclones affecting Iran showed that although the number of cyclones increased from the 1st to the last decade, the origins of cyclones in the 1st decade were mainly in the Mediterranean Sea and the Red Sea. In the following decades, the diversity of the origins of the cyclones was one of the decades' characteristics. In addition, from the 1st to 3rd decade, the cyclone centers (excluding the Red Sea-Sudanese cyclones) took a more northerly route. This decadal variation in cyclones' characteristics might lead to the decadal variation of PI in Iran. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.