Analysis of the effectiveness of precipitation anomalies during the occurrence of extreme and extreme droughts in the south of Iran in the last three solar cycles.

In this research, the historical trend and effectiveness of rainfall anomalies during severe and extremely severe droughts in southern Iran have been investigated. For this purpose, the daily and annual rainfall data of the synoptic stations of the study area were extracted from the data of the Meteorological Organization. The statistical base has been chosen to adapt to the solar cycles of a 33-year period corresponding to the years 1986-2019. Based on this, 34 synoptic stations of the region were consistent with this statistical period. First, the state of droughts was investigated based on Standard Rainfall Index (SPI), Chinese Z (CZI), and ZSI (ZSI) score. RAI index has been used to check precipitation anomaly. The selection criteria of 7 years were chosen as examples of extreme and extreme droughts. The historical trend of the occurrence of droughts showed that, firstly, in the last three cycles, in 26 years out of 33 years of the statistical period, the southern region of Iran has more or less faced the phenomenon of drought. The number of droughts in the last two cycles has increased greatly. So that in cycle 23 out of 11 years, 9 years and in cycle 24 out of 11 years, 10 years, many parts of the region were affected by drought. In both cycles in 4 years in more than half of the stations severe and super severe drought occurred. In terms of rainfall-related phenomena, severe anomalies have also occurred in the southern region during droughts, the average daily rainfall is greatly decreasing compared to the long-term average rainfall of the region. In other words, the distribution of rainfall per unit of time has decreased. So that the average daily rainfall in the rainy season has decreased from two millimeters to less than one millimeter.