In complex hydrological regions, single drought indices, such as the Standardized Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration Index (SPEI), the Vegetation Condition Index (VCI), and the Vegetation Health Index (VHI) may not be fully sufficient for monitoring composite drought events. Therefore, in this study, a new composite drought index (CDI) that uses nested copula functions to integrate precipitation, the normalized difference vegetation index (NDVI), and temperature was proposed, and its reliability was tested and applied in Liaoning Province, China. The results indicated that: (1) The CDI correlates well with SPI, SPEI, VCI, and VHI, showing high sensitivity, specificity, and over 87% consistent hit rate in monitoring drought events. (2) Southern and western mountainous areas face long, severe droughts at the 3-month scale, while southwestern and southern coastal areas experience severe droughts at the 12-month scale. (3) Summer droughts are worsening, while other seasons show alleviation. However, over half of the region may face severe droughts in the future, except in spring. (4) NDVI is the primary factor influencing interannual summer and winter drought trends, while PET is the primary factor influencing spring and autumn drought trends. Our results on the new drought index, which help formulate drought response strategies in the context of climate warming, are of great significance for understanding the future trends of drought and its influencing factors.
Zhong et al. (Fri,) studied this question.