Water-Constrained Revegetation Potential in China’s Drylands Using a Multidata Ensemble Approach

Abstract Revegetation mitigates climate change through carbon sequestration but intensifies water conflicts between ecosystems and human demands in water-limited regions. This study quantified not only the revegetation potential but also the allowable vegetation conversions in China’s drylands under water constraints using a multidata ensemble approach. The ensemble estimate of available water resources (AWR) was 65.4 ± 13 mm [median ± standard deviation (SD)] in water surplus areas (covering 55% of the region) and −39.1 ± 7 mm in water deficit areas of China’s drylands averaged over 2003–18. The ensemble of nine precipitation and evapotranspiration data combinations effectively reduced estimation uncertainty compared with most single-dataset combinations. Under current water constraints, the median estimate of gross primary productivity gain associated with revegetation ranged from 4% to 7% across the drylands depending on vegetation types and 12%–17% in water surplus areas (forests: 14%, grasslands: 17%, both irrigated and rain-fed crops: 12%). Crucially, in water surplus areas, vegetation conversions toward higher water consumption types were feasible. In contrast, in most water deficit areas, the deficit cannot be fully offset by converting existing vegetation to less water-intensive types, suggesting a critical deficit under the current accounting framework. Future revegetation potential will increase with improved water use efficiency and rising AWR under the impacts of climate change. Our research highlights the importance of water constraints on revegetation and the vegetation-specific water costs and carbon benefits, which are critical to implementing natural climate solutions while ensuring water sustainability. Significance Statement Revegetation is a key natural climate solution but risks intensifying water stress in drylands. This study maps where and how much vegetation increase can be sustainably supported across China’s drylands under water constraints. Using a multidataset ensemble that effectively mitigates the high uncertainty of single-data approaches, we found that over half of the region retains a water surplus, allowing for vegetation growth that could increase carbon uptake by up to 17%. However, in water deficit areas, vegetation conversion alone cannot offset the deficit. Our findings provide a credible water budget for drylands, emphasizing that revegetation or vegetation conversion plans must align with water availability to secure carbon and water sustainability.