Assessment of compound extremes using statistical methods in India

Extreme events are becoming more frequent, intense, and prolonged, with significant impacts on human lives, the environment, and regional development. Rising temperature due to global warming is one the crucial factors causing the rise in the frequency and severity of extreme events. The worst extreme events are caused by a combination of more than one factor/variable, which makes it essential to study the co-occurrences of extremes, also known as compound extremes. In the present study, four compound extremes are assessed over India for the time period of 1971-2020 using two different statistical approaches, empirical approach, and multivariate distribution analysis. The variables used are temperature and precipitation, having a resolution of 0.25° × 0.25°. Firstly, the empirical analysis of four compound extremes, Hot-Dry, Hold-Wet, Cold-Dry, and Cold-Wet, is done by providing threshold percentiles (25^th and 75^th) to count the exceedance, and Mann Kendall's trend, p-value, and Sen's slope are calculated to assess the changes and significance of the extremes. Next, multivariate distribution analysis using Copula is conducted to study the dependency between temperature and precipitation. The results indicate a significant increase in compound Hot-Dry and Hot-Wet extremes across the country, with a decrease in Cold-Dry and Cold-Wet conditions. The changes in extremes are more pronounced in the later period (1996-2020) than in the earlier period (1971-1995). This study provides insight into the evaluation of compound extremes in India over the past 50 years, which can help us understand the changes and frequency of their occurrence.