A novel index to quantify land-atmosphere coupling: asymmetric response of hot-dry and cold-wet compound extremes.

Compound hot-dry and cold-wet extreme events can pose severe threats to human health, social economy, and agricultural production, with their synergistic impacts far exceeding the linear integral of individual events. Land-atmosphere coupling is a key physical process impacting these extremes. However, limitations persist in current studies for quantifying its strength, and the different roles and sensitivities in hot-dry and cold-wet events remain poorly understood. To address these gaps, this work innovatively employs a data-driven Dynamical Systems Method to establish a novel framework for the objective and instantaneous quantification of land-atmosphere coupling globally. Utilizing this framework, this research aims to evaluate the sensitivity of global summer compound hot-dry and cold-wet extremes to land-atmosphere coupling and reveal the spatial patterns of their asymmetric responses. Furthermore, the key local physical processes and large-scale atmospheric circulation modulating mechanisms underlying the observed asymmetries are analyzed through multi-perspective attribution. The results of this project can significantly contribute to the understanding of the relationship between land-atmosphere coupling and compound extremes, providing crucial support for decision-makers to enhance resilience against these complex extremes and to formulate targeted prevention and mitigation strategies.