Application of L-Moments for Regional Frequency Analysis of Monthly Drought Indexes

For evaluating the severity of drought in a certain month, two indexes of cumulative precipitation deficit (CPD) and maximum precipitation deficit (MPD) are used such that a regional frequency analysis has been carried out by L-moments. These measures of drought are strongly related to moisture deficits for the vegetation during the growing season. In this paper, 11 synoptic stations in Isfahan province, Iran, with a semiarid environment are used. The stations have a minimum of 10 years of data. The two drought indexes are calculated for all of them in whole months. The WeatherMan tool is used for completing missing data. The Food and Agriculture Organization of the United Nations Penman-Monteith (FAO-PM) method is used for calculating reference evapotranspiration [ET(FAO-PM)]. According to previous studies, this method is suitable for this region. The Hosking homogeneity test is applied for identifying a homogeneous region. The Hosking goodness-of-fit test is performed to select the best regional distribution. The results show that the region is homogeneous in months 5 to 10, and in the rest of the months, the region becomes homogeneous after using clustering techniques and dividing the region into two smaller regions. Also, the best regional distribution is distinguished generalized logistic in the most months. Therefore, the severity of drought is estimated with various return periods by CPD and MPD. The maximum intensity of drought in the all stations happens in months 6 to 8, which are in late spring to midsummer. The severity of drought in Ardestan, Khoorbiabanak, and Naeen stations is greater than the remaining stations. Using the outcome of this study, the amount of required water can be estimated for agriculture each month, and the amount of water available is effectively managed in this province. DOI: 10.1061/(ASCE)HE.1943-5584.0000396. (C) 2012 American Society of Civil Engineers.