An Assessment of Hydrological Drought in the Province of Kurdestan Using the Threshold Method

Occurrence of recurrent and prolonged meteorological droughts is the rule rather than the exception in the Land of Iran. These events, which are usually followed by hydrological and agricultural droughts, are the most disastrous natural phenomenon that may happen to any dryland. Associated food shortages that may end in famine have been repeatedly experienced in Africa during the past 50 years. Exponential population growth entails a higher demand for the limited water resources; therefore, the prudent management of these resources urges the water-related authorities to collect reliable data and analyze them thoroughly to plan and implement hydraulic structures and distribution systems. I (we?) used the threshold method (truncation level) to analyze the flow of 4 gauged rivers at the GharehGuni, Duab-e-Nowsood, Panbeh Daneh, and Pol-e- Adinan hydrometry Stations. Qά in the application of the threshold method signifies the minimum flow where ά percentiles of the data exceed that level. The interior criterion method was also used to eliminate the minor droughts and pool (cluster?) the same magnitude (dependence?) droughts. The results of frequency analysis indicated that the mean deficit volume was 17.7 million cubic meters, and the mean drought duration was 76 days. The best distribution models for the drought-related deficit volume were those of Johnson and Pearson, and for the drought duration were Johnson and exponential. The mean return period for the hydrological drought was 4 years based on these distribution models.