Changing water availability and demand shift global greening to regional browning

The Earth is greening in many regions due to increased temperature, higher atmospheric CO₂ concentration, and land use change. However, while climate change has been accelerating, greening has not kept pace in many regions. Here, we show that decreasing water availability and increasing atmospheric water demand are regionally coinciding with browning trends over recent decades. In affected tropical regions, a regression analysis considering a comprehensive set of hydro-meteorological variables confirms that both water availability and atmospheric water demand are dominant drivers of inter-annual variability in Leaf Area Index (LAI). Earth system models mostly reproduce the observed spatial extent of browning and related coinciding water changes in the multi-model mean, while simulations from individual models differ strongly. Our results provide a new constraint for related model development and underscore the need for enhanced monitoring and consideration of observation-based water availability trends as an emerging driver of vegetation in future analyses and model development.