Spatially compounding climate extremes and environmental risk: cross-regional synchrony, spatial buffering loss, and systemic consequences

Spatially compounding climate extremes are increasingly recognized as a source of climate-related risk, and their risk significance depends on how synchrony affects connected systems. The critical transition occurs when cross-regional synchrony reduces support from places that would otherwise buffer one another through substitution, reserve capacity, mutual assistance or recovery support—a condition we term spatial buffering loss. This Topical Review synthesizes empirical and methodological evidence to examine how synchrony is generated, when it translates into functional loss, and what is required to assess that transition. Food production, water allocation and firefighting cooperation provide complementary settings for examining substitution, reserve and assistance functions, while the synthesis distinguishes joint exposure from support available to recipients. Atmospheric circulation, persistent weather patterns, land–atmosphere feedbacks and hydrological connectivity can organize synchrony; functional evidence determines whether that synchrony reduces compensating support and produces systemic consequences. Accordingly, credible assessment must connect event topology and joint-tail behaviour with functional exposure, an explicit compensating relation and a counterfactual estimate of support that would otherwise have remained available. By linking event organization to recipient support, the synthesis provides a functional basis for assessing spatial buffering loss across connected systems. This perspective connects the evidence to decisions about supplier diversification, reserve operation and mutual assistance.