Changing Pattern of Drought Proneness Across Iran

The present study aims to investigate a trend of long-term changes in drought proneness in Iran. For this purpose, we first evaluate the reliability, resilience, and vulnerability (RRV) based on the gridded data of soil moisture of the Climate Prediction Center (CPC), NOAA, for 64 years (1955–2018) within the Iranian political boundaries. The mutual relations of reliability, resilience, and vulnerability were analyzed through the Kendall-Tau correlation coefficient. It was shown that the combination of reliability and vulnerability could be the best combination for developing the Drought Management Index (DMI) on Normal copula. In addition, the long-term trends of change in drought proneness were evaluated through various fuzzy regression models in the framework of DMI. The results of trend analysis indicated that disregarding the northern and western halves of the country, which lack any trend, the long-term trends of change in drought proneness have been increasing in the eastern, southeastern, and central parts, in a way that the highest increasing trend gradient in these regions was 0.0038 for 5-year periods (or 0.228 for the whole 64 years). This increasing trend indicates the higher drought proneness for these areas.