Increasing water limitation of global ecosystems in a changing climate

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The ongoing and projected climate change involves changes in temperatures and precipitation in many regions. These changes in turn affect terrestrial ecosystems that require sufficient water and energy to provide essential services such as food security and the uptake of human-caused CO2 emissions.This presentation will introduce the concept of ecosystem water and energy limitation, and identify areas where each limitation prevails. These areas are characterised by different sensitivities of evapotranspiration and vegetation productivity to long-term changes in temperature and precipitation. A special focus will be on the global trends of ecosystem water limitation through time, where our results show increased water sensitivity across recent and future decades in many regions. This implies an increasing ecosystem vulnerability to water availability which can lead to reductions in vegetation carbon uptake in the future, consequently amplifying climate change. In this context, near-surface soil moisture is found to be the most relevant water reservoir for vegetation functioning, while deeper soil moisture is less relevant for the investigated multi-decadal time periods.The presentation will also illustrate that the increasing water limitation can affect the consequences of droughts in related regions. These ecosystems become more vulnerable to droughts such that disruptions in vegetation functioning are more pronounced. Also evaporative cooling will decrease more strongly which promotes hotter temperatures during drought. At the same time, decreased vegetation productivity could lead to reduced availability of fuel for wildfires.These analyses are based on (i) observation-based data including reanalyses, satellite-based datasets and gridded data derived from upscaling in-situ observations, and (ii) simulations from land surface and Earth system models. Building upon this, the presentation will discuss the related model performance as well as opportunities for model development to more accurately capture and predict ecosystem water limitation.