Causal Dynamics of Land–Atmosphere Coupling under Compound Dry–Hot Events

The increasing frequency and magnitude of compound dry–hot events (CDHEs) pose significant risks to natural and managed systems. While the role of land–atmosphere coupling in determining the magnitude and evolution of CDHEs has been highlighted, the causal interactions between variables within the coupled system under external forcing remain poorly understood. This study investigates the causal relationships between soil moisture and 2m air temperature, as well as between absorbed shortwave solar radiation and 2m air temperature during CDHEs, based on information flow theory. Using two fully coupled simulations with the Terrestrial Systems Modeling Platform (TSMP), one with and one without irrigation, the information flow analysis provides an interpretable framework to characterize the spatiotemporal variability of the land–atmosphere coupling strength in response to the perturbations such as CDHEs and irrigation. 

The results show that concurrent dry and hot conditions are characterized by temporal shifts in the evaporative regime towards increased soil moisture–temperature information flow driven by the shift in surface energy partitioning, such that decreases in soil moisture lead to increased temperatures. Meanwhile, irrigation can significantly reduce the frequency and magnitude of CDHEs by directly increasing soil moisture variability and indirectly affecting surface energy fluxes, and thus altering land–atmosphere coupling. However, the impact of irrigation in Europe is predominantly local and limited by the volumes applied. These findings highlight the potential of targeted, region-specific irrigation strategies to attenuate dry and hot extremes. In addition, the information flow framework provides a robust and interpretable tool for diagnosing the functional performance of regional climate models under perturbations, offering new insights for analyzing the impacts of human interventions on the climate system and enhancing our understanding of extreme hydroclimatic events in future studies.