Photosynthesis sensitivity to cloud cover is shaped by aridity on a global scale

Energy and water are two essential requirements for photosynthesis, and clouds influence both simultaneously by altering radiation and precipitation. Cloud-induced reductions in surface solar radiation and enhancements in precipitation have contrasting effects on photosynthesis. In our study, eddy covariance measurements, satellite observations and dynamic global vegetation models are used to examine the response of photosynthesis to cloud cover on a global scale. The results show that the photosynthesis sensitivity to cloud cover varies across ecosystems, and its global pattern is highly associated with aridity. Specifically, in water-limited dry regions, clouds promote photosynthesis by forming precipitation, while in energy-limited humid regions, clouds inhibit photosynthesis by blocking sunlight. The spatially dependent sensitivity of photosynthesis to cloud cover is further used to estimate projected changes in vegetation productivity driven by clouds.