Exploring Copula‐Based Approaches for Analyzing Compound Hydroclimatic Extremes

Extreme hydrological events such as floods, droughts, and heat waves pose substantial threats to society and ecosystems. These events often exhibit complex interactions, especially when multiple extremes unfold simultaneously or in succession. Traditional univariate approaches often fail to account for interdependencies among hydroclimatic variables, thereby overlooking potential compound effects. In contrast, copula-based methods offer a flexible and robust framework to model multivariate dependencies by characterizing marginal distributions and dependence structures separately. This chapter provides a concise overview of the key principles of copula theory and a systematic review of its applications in hydroclimatic research. Furthermore, we present a methodological framework for analyzing compound hydroclimatic extremes, illustrated through a case study conducted over mainland India. Utilizing a newly developed copula-based Joint Extreme Index (JEI), we evaluate hot-dry and hot-wet extremes across historical (1951–2020) and future (2021–2100) periods. The findings reveal a notable increase in the frequency and spatial extent of these extremes in recent decades and project a doubling of such occurrences under a high-emission scenario (SSP5-8.5), particularly in the Indo-Gangetic Plains and southern regions. In essence, this chapter underscores the theoretical aspects and applications of copulas, demonstrating their efficacy in quantifying and projecting hydroclimatic extremes, thereby allowing more reliable risk assessments and informed policymaking in a rapidly changing climate.