Abstract
Drought is one of the natural disasters that causes a great damage to the human life and natural ecosystems. The main differences are in the gradual effect of drought over a relatively long period; impossibility of accurately determining time of the beginning and end of drought; and geographical extent of the associated effects. On the other hand, lack of a universally accepted definition of drought has added to the complexity of this phenomenon. In the last decade, due to increasing frequency of drought in Iran and reduction of water resources, its consequences have become apparent and have caused problems for planners and managers. Therefore, in this study, to investigate severity and duration of meteorological, hydrological and agricultural drought in Karkheh River basin, regional frequency analysis of standardized precipitation index ( SPI ), standardized evapotranspiration index ( SEI ), standardized runoff index ( SRI ) and standardized soil moisture index ( SSI ) was performed using L-moments. Then, using Hosking and Wallis heterogeneity test, basin was divided into four homogeneous areas. After that, based on the Z statistic of goodness-of-fit test for each distribution, the best regional distribution function for each homogeneous region was selected. The results showed that hydrological drought occurs with a very short time delay in Karkheh River Basin after the meteorological drought and two indicators show meteorological and hydrological drought conditions well. Agricultural drought occurs after meteorological and hydrological drought, respectively, and its severity and duration are less than the other indicators. Meteorological, hydrological and agricultural droughts do not occur at the same time in all of the years and in general, the SPI drought Index shows the most severe droughts compared with the other three indices.
Regional Frequency Analysis of Extremes Precipitation Using L-Moments and Partial L-Moments