Evaluating the Characteristics of Multiyear Extreme Droughts in Semi-Arid Regions
Following the unconditional definition of drought events, this study presents general mathematical expressions that can be used to evaluate the occurrence probability and the return period of multiyear drought events of extreme magnitude evolved after truncating low order dependent hydrological or meteorological processes. The drought magnitude was fitted using the gamma distribution and the drought run length was defined unconditionally regardless where the run starts as long as it satisfies the continuity. Considering the joint analysis of the drought magnitude and the run length, the characteristics of the multiyear drought of extreme magnitude achieved theoretically was found to match well with empirical results obtained after analyzing the simulated and historical precipitation. After truncating the annual rainy season precipitation for Madaba region in Jordan, the 6-year extreme historical drought that occurred in 1958–1963 was a rare event recurring every 226 years. In the semi-arid region of Madaba, meteorological drought events of a short duration, 2–3 years, and a precipitation deficit of 149 mm or less are frequent events with 7–10 years return period, while events of 4 years or more, tested at deficit threshold of 149 mm, are less frequent events regardless of their magnitude.
KeywordsDrought Occurrence probability Return period Sustainable resources
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