How do the world’s highest rainfall regions respond to compound climate extremes?

Compared to extremes of a single hydroclimatic variable, compound temperature–precipitation extremes can exert stronger influences on hydrological systems, yet their behaviour in the world’s highest rainfall regions remains insufficiently examined. This study investigates how one of the world’s highest rainfall region responds to both individual and compound climate extremes under present and future climate conditions. Gridded observations and CMIP6 projections are analyzed using standard ETCCDI indices and developed five Joint Extreme Indices (JEIs) to evaluate the spatial and temporal evolution of joint extremes. Results show that Consecutive dry days (CDD) increase by about ∼4 days, indicating greater rainfall intermittency. Temperature extremes also show consistent warming, with temperature increasing by 4–5 °C and summer days (SU) increasing by ∼30–55 days in the far future. Individual extremes combine to substantially amplify compound hazards as reflected in the JEIs. Hot–dry conditions (JEI₁) become roughly 3–4 times stronger than the baseline. Hot–wet extremes (JEI₂) exhibit the most pronounced amplification, increasing by about 6–7 times due to the concurrence of higher temperatures and intense short-duration rainfall. Warm night–heavy rainfall events (JEI₃) also intensify, becoming approximately 4–5 times stronger. In contrast, cold–wet extremes (JEI₄) show only minor changes and remain relatively weak. Meanwhile, summer storm conditions (JEI₅) strengthen markedly, reaching roughly 5–7 times their historical magnitude, highlighting the increasing interaction between heat and heavy rainfall. Overall, the findings indicate that the response of this high-rainfall region to climate change increasingly involves the combined occurrence of temperature and rainfall extremes.