A composite index coupling five key elements of water cycle for drought analysis in Pearl River basin, China

Drought, as a natural disaster, has widespread consequences and is notoriously difficult to manage. Critical to developing a drought management strategy is the identification and assessment of drought. To that end, this study developed a new composite index, called the standardized water cycle index (SWCI) based on the water cycle and water balance. The SWCI couplesd the key elements of the water cycle, including precipitation, evapotranspiration, leaf area index, surface runoff, and subsurface runoff, and requires the joint distribution of these elements which was determined using the D-vine copula. The Kendall transform was used to reduce the dimensionality of the five-element joint probability density function, which was then inversed to obtain the SWCI which was then evaluated with the data from the Pearl River basin obtained using the CMIP6. Results showed that the SWCI satisfactorily evaluated drought conditions, while reflecting the drought-mitigating effect of vegetation and subsurface runoff. The SWCI was also able to evaluate drought in areas with a high level of human activity.