Drought Assessment Using Two-Variate Modelling

Abstract

Drought is a natural hazard that mainly threatens water resources and food security. Due to climate change, an increase in drought events that may adversely affect various sectors is expected. Therefore, a reliable analysis of drought events is important. However, there is a deficiency in research works which deals with two-variate drought assessment and monitoring. This paper focused on drought assessment based on modelling the effective precipitation and runoff variables simultaneously. Drought indices are widely utilized to assess droughts in many regions around the world. The copula method was used to modelling a two-variate drought index based on the effective precipitation and runoff variables in northern Iraq as a case study. It was found that Frank is the optimal copula function to model the joint cumulative distribution function of effective precipitation and runoff. To assess the performance of the proposed two-variate index, it was compared with the widely used standardized precipitation index SPI and Standardized Runoff Index SRI. Where the Pearson correlation coefficients between 2-variate index and SPI, SRI were 0.78 and 86, respectively, for 3-month time scale, and were 0.83 and 82, respectively, for 6-month time scale. The results revealed that the proposed index is applicable and can comprehensively and effectively characterize drought events.