Analyzing Iran’s Local and Regional Droughts Using the Theory of Runs and Standardized Precipitation Index (SPI)

The primary objective of the present study is the investigation of the various properties of Iran’s local and regional droughts based on the theory of runs and standardized precipitation index (SPI). Thus, in order to accomplish this goal, the annual precipitation data of 63 synoptic stations were procured from Iran’s meteorological organization for a 30-year period (1986-2015).. First, based on the theory of runs and SPI index, local and regional drought characteristics such as duration, cumulated deficit and their severity were extracted.. Detection and separate of regional droughts based on critical spatial threshold were selected 30 and 50% of the total area of Iran, and based on this, the characteristics of Iranian drought for both scales were examined together. In local scale, the droughts were monitored using the theory of runs and it was found out that this method cannot be an appropriate one for regions featuring high vastness and various climates in comparison to SPI. It was also shown in regional scale that the use of the theory of runs with areal threshold of 30% of the total area under drought cannot make up a suitable combination for monitoring Iran’s regional droughts. Thus, in a comparison between the two areal thresholds of 30% and 50%, it was figured out that the 50% areal threshold is a good one for the theory of runs and SPI for monitoring Iran’s regional droughts. Another result of this study is that the duration of droughts in the first period was shorter than the second period.. As for the intensity of the droughts, it seems that the intensity of the droughts is lower in the second half (2001-2015) as compared to the first half (1986-2000).