Drivers of Global Shifts in Ecosystem Energy and Water Limitation: The Role of Evolving Vegetation Sensitivity to Water Stress

Terrestrial ecosystems play a foundational role in modulating the global hydrological cycle and sequestering atmospheric CO2. Their functional integrity, however, is increasingly challenged by shifting environmental constraints on soil moisture and energy availability. While recent decades have seen significant advances in Earth system modeling and remote sensing, the precise mechanisms by which climate change alters vegetation sensitivity to water stress—and subsequently drives shifts in hydrological regimes—remain a subject of ongoing investigation. This study investigates long-term spatial and temporal transitions between energy-limited and water-limited regimes at a global scale from 1950 to 2025. To address the inherent uncertainties in multi-source datasets, we employ a robust collocation analysis that integrates remote sensing products with high-resolution reanalysis data. By applying a joint-solution methodology alongside an array of sensitivity experiments, we seek to disentangle the respective influences of climatic forcing and vegetative feedbacks on observed hydrological shifts. Our preliminary findings suggest a discernible historical transition in eco-hydrological dynamics. There is evidence of a contraction in energy-limited regions, potentially linked to increasing surface net radiation. Notably, the data indicates that areas experiencing a simultaneous increase in radiative demand and a decline in root-zone soil moisture are most susceptible to transitioning toward water limitation. Furthermore, our initial analysis points toward a strengthening coupling between vegetation transpiration and root-zone soil moisture, which may act as a critical feedback mechanism. These emerging results underscore the potentially pivotal role of evolving vegetation sensitivity to water stress in reshaping global ecosystem-water dynamics. By refining our understanding of these energy-water regime shifts, this work aims to contribute to more accurate benchmarking of Earth system models and provide insights into the resilience of regional hydrological systems under a changing climate.