# Hydroclimate shapes photosynthetic sensitivity to cloud cover across global terrestrial ecosystems

## TL;DR

Clouds influence photosynthesis differently in dry and wet regions, and climate change may shift plant productivity from arid to humid areas.

## Contribution

The study reveals how cloud cover's impact on photosynthesis varies with hydroclimate and predicts future changes in vegetation productivity.

## Key findings

- Clouds promote photosynthesis in arid regions by increasing precipitation with a delayed effect.
- Clouds inhibit photosynthesis in humid regions by blocking sunlight almost instantly.
- Climate warming is projected to shift vegetation productivity from arid to humid regions due to cloud cover changes.

## Abstract

Vegetation photosynthesis primarily depends on surface energy and water availability, both of which are simultaneously regulated by clouds through radiation and precipitation, respectively. However, the net impact of cloud-induced changes in surface solar radiation and precipitation on photosynthesis remains elusive. Here, using observational- and model-based datasets spanning the past few decades, we show that, consistently across scales from site-level eddy covariance measurements to global-scale gridded datasets, the sensitivity of photosynthesis to cloud cover is spatially shaped by the hydroclimate, as quantified by the humidity index (mean annual precipitation-to-evapotranspiration ratio). Specifically, we find that in water-limited arid regions, clouds promote photosynthesis through increased precipitation, with a delayed effect typically within one month, whereas in energy-limited humid regions, they inhibit photosynthesis almost instantaneously by blocking sunlight. An annual scale spatially resolved sensitivity metric of photosynthesis to cloud cover is further examined to estimate potential changes in vegetation productivity driven by clouds. The findings indicate that, under a warming climate, particularly in the Coupled Model Intercomparison Project Phase 6 “ssp585” scenario (2015–2099), gross primary productivity is projected to decline in arid regions and increase in humid regions due to changes in cloud cover, suggesting an exacerbation of regional disparities in ecosystem functions.

Clouds affect photosynthesis differently across hydroclimates: they enhance it in arid regions but reduce it in humid regions. With climate warming, changes in cloud cover shift vegetation productivity from arid to humid regions.