Abstract: To reveal the regional overall drought degree and its change characteristics, a regional drought comprehensive index (MIDI) was constructed by using the dynamic weight coefficient method based on the calculation results of standardized precipitation index (SPI), standardized runoff index (SZI) and standardized regional water shortage index (SSDI). The applicability of MIDI was analyzed and verified according to historical drought statistics such as drought-affected area rate and reduced water supply due to drought. With the measured data of eleven meteorological stations and twelve hydrological stations of Changsha-Zhuzhou-Xiangtan region in recent decades as input, the drought events were identified by using run length theory and Copula function method, and their occurrence frequency was calculated. Furthermore, the evolution characteristics of regional comprehensive drought were analyzed by using trend analysis method. Results manifested that SPI, SZI and MIDI index have their own advantages in drought evaluation for different water sources and industry types. The annual cumulative drought intensity of SPI and SSDI is highly correlated with the rate of drought-affected crop area; while the annual cumulative drought intensity of SZI is highly correlated with urban water supply reduction due to drought, hence is more suitable for assessing the drought of urban area which is relied on surface runoff as the major water supply source. The dynamic weight coefficient method proposed in this study reflects the leading role of single drought index in different stages by taking the interannual change of regional industrial structure and the seasonal change of industrial water demand regularities into consideration. It is suitable for the comprehensive regional drought evaluation of various water sources and industrial types. Last but not the least, the MIDI of Changsha-Zhuzhou-Xiangtan region was examined from monthly, seasonal and yearly scales, and results unveiled that the frequency of extreme drought in Changsha-Zhuzhou-Xiangtan region has been increasing fluctuatingly in the recent two decades.

Key words: comprehensive index of drought, drought evolution, drought assessment, drought frequency, Changsha-Zhuzhou-Xiangtan region