As physical parameters, different rainfall types can affect rainfall amount and frequency, and subsequently, the strength and weakness of wet and dry spells under different atmospheric conditions. In this study, stratiform and convective rainfall in the mountains, plains, and southern seas of Iran are estimated across all seasons using 17 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data to understand rainfall type variability and the ratio of each rain type during wet and dry spells. The results show that the maximum of both rainfall types occurs over the northern coastal plains and mountains, while its minimum is over the southern seas and inland plains. The highest (lowest) contribution of convective rain rate is over the northern coastal plains (inland plains) and about 85% (64%) in winter. The frequency of convective rain rate peaks in summer for all regions except for the northern coastal plains. Stratiform rain rate has a higher contribution over the mountains, which is about 31%. The maximum frequency of stratiform rain rate is also in winter, except for the northern coastal plains. The Mann–Kendall trend analysis shows that stratiform rainfall has an increasing trend of about 0.1 mm/h/decade in all regions except in inland plains. However, each region has its own season for significant increasing trend. The analysis of dry and wet spells suggests that convective rainfall is pronounced in wet January, while stratiform rainfall is noticed in wet June. To explain both rainfall types, analysis is further made to the atmospheric-driven large-scale circulation in terms of the explanatory abilities of each circulation parameter in determining rainfall types. It is found that the zonal wind component, geopotential height at 850 and 500 hPa and mean sea level pressure manifest a determining role in shaping the rainfall types in wet January, while the specific humidity at 850 hPa and meridional wind component show the highest effect in wet June, especially over the mountains and southern seas. For stratiform rainfall, the explanatory role of each large-scale circulation parameter is prominent. These findings contribute to better understanding the spatial variation of each rainfall type in the context of wet and dry spells over Iran.

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