Regime Shifts During Compound Drought‐Heatwave Events Amplify Ecosystem and Heat Stress Risks

Abstract Compound drought‐heatwave events (CDHEs) can cause severe ecological and socioeconomic impacts worldwide. However, their mechanisms are often inferred from seasonal statistics or event‐mean composites that obscure within‐event process evolution. Here we develop a daily regime‐based framework to characterize global summer CDHE lifecycles using reanalysis data from 1961 to 2022. Most events remain within a single thermodynamic regime, whereas a recurrent minority undergoes within‐event regime shifts. The two leading transition pathways remain far less frequent than steady pathways, but events following them last longer, are more severe, and have increased significantly over recent decades. Sunny‐Humid to Advective transitions are linked to strengthened warm air transport and amplified human heat stress, whereas Sunny‐Humid to Sunny‐Dry transitions reflect a shift toward moisture‐limited conditions and larger declines in ecosystem productivity. Accounting for daily process evolution can therefore improve assessments of compound drought‐heatwave risks in a warming climate.