Bivariate analysis of meteorological drought duration and severity (case study: Kermnashah province)

Drought is one of natural disaster that is related to prolonged decrease of humid in a region. Meteorological drought is related to prolonged decrease of precipitation and has several characteristics (severity, duration, magnitude). These characteristics are dependent and because of this correlation, drought monitoring based on one characteristic cannot fully represent region conditions. Thereby the best method is monitoring of drought characteristics jointly. In this research, meteorological drought was analyzed in Kermanshah province based on two characteristics, i.e. severity and duration using multivariate copulas function. Three families of Archimedean copulas were fitted to drought severity and duration. Gumble copula was selected as the best fit. Finally, the joint probability and return period are determined using Gumble copula in the study area. The results showed, sever drought has occurred in the western part of region with 259.3 mm severity and 18 months duration. Based on bivariate analysis, this drought has lowest probability and biggest return period then other droughts in this region.