Future socio-ecosystem productivity threatened by compound drought-heatwave events

Compound drought-heatwave (CDHW) events are one of the worst climatic stressors for global sustainable development. However, the physical mechanisms behind CDHW and their impacts on socio-ecosystem productivity remain poorly understood. Here, by combining satellite observations, field measurements and reanalysis, we show that terrestrial water storage and temperature are negatively coupled, likely driven by similar atmospheric conditions (e.g., water vapor deficit and energy demand). Using simulations from a large climate-hydrology model ensemble of 111 members, we demonstrate that the frequency of extreme CDHWs is projected to increase by ten-fold globally under the highest emissions scenario, along with a disproportionate negative impact on vegetation and socioeconomic productivity by the late 21^st century. Limits on water availability are likely to play a more important role in constraining the terrestrial carbon sink than temperature extremes, and over 90% of the global population and GDP could be exposed to increasing CDHW risks in the future, with more severe impacts in poorer or rural areas. Our results provide crucial insights towards assessing and mitigating adverse effects of compound hazards on ecosystems and human well-being.