Identification of Iran's rainy season and its relation to some spatial features

Abstract

AbstractIdentifying the rainy season (RS) is significantly important from the meteorological, hydrological and socio‐economic points of view. In the current study, the climatology of Iran's RS was identified based on developing a definition by mainly relying on examining daily rainfall observations from 2188 stations in the period of January 1, 1971–December 31, 2015 (45 years). Accordingly, it was revealed that at most two RSs could be distinguished in Iran; and there was a widespread rainy season (WRS) covering the entire country in three consecutive months (phases). In the northwest of the country, the Alborz Mountain chains, and in the southeast of Iran, the RS was mainly interrupted by a dry season. Therefore, two RSs occurred in these areas (widespread and regional rainy seasons [RRS]). The four withdrawal phases of the RS were relatively different on the regional scales. However, they generally showed a relation with latitudes. Unlike the onset date of phases of the RS, these phases did not occur at the same intervals. The diversity of spatial factors in Iran (including geographic coordination, topographic features and sea surface temperature of surrounding seas) caused the spatial diversity of the timing of the RS. Consequently, linear relationships could not illustrate the nature of the spatial pattern of this diversity. The linear spatial relationship was statistically significant only for the onset date of the RS. The regression model used in the present study showed that despite the effect of local factors on the onset date of the RS, the major regional differences could be attributed to systems and mechanisms that probably affected the onset date of the RS from outside of the country.