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Despite the growing interest in predicting global and regional trends in vegetation productivity in response to a changing climate, changes in water constraint on vegetation productivity (i.e., water limitations on vegetation growth) remain poorly understood. Here we conduct a comprehensive evaluation of changes in water constraint on vegetation growth in the extratropical Northern Hemisphere between 1982 and 2015. We document a significant increase in vegetation water constraint over this period. Remarkably divergent trends were found with vegetation water deficit areas significantly expanding, and water surplus areas significantly shrinking. The increase in water constraints associated with water deficit was also consistent with a decreasing response time to water scarcity, suggesting a stronger susceptibility of vegetation to drought. We also observed shortened water surplus period for water surplus areas, suggesting a shortened exposure to water surplus associated with humid conditions. These observed changes were found to be attributable to trends in temperature, solar radiation, precipitation, and atmospheric CO₂. Our findings highlight the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.

Drought is one of the most important natural hazards impacting ecosystem carbon cycles. However, it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. First, drought impacts can have different time dimensions such as simultaneous, cumulative, and lagged impacts on ecosystem carbon balance. Second, drought is not only a multiscale (e.g., temporal and spatial) but also a multidimensional (e.g., intensity, time‐scale, and timing) phenomenon, and ecosystem production and respiration may respond to each drought dimension differently. In this study, we conducted a comprehensive drought impact assessment on ecosystem productivity and respiration in humid regions by including different drought dimensions using global FLUXNET observations. Short‐term drought (e.g., 1‐month drought) generally did not induce a decrease in plant productivity even under high severity drought. However, ecosystem production and respiration significantly decreased as drought intensity increased for droughts longer than 1 month in duration. Drought timing was important, and ecosystem productivity was most vulnerable when drought occurred during or shortly after the peak vegetation growth. We found that lagged drought impacts more significantly affected ecosystem carbon uptake than simultaneous drought, and that ecosystem respiration was less sensitive to drought time scale than ecosystem production. Overall, our results indicated that temporally‐standardized meteorological drought indices can be used to reflect plant productivity decline, but drought timing, antecedent, and cumulative drought conditions need to be considered together.