Overwhelming wetland reclamation confronts severe flood risks.

Agricultural expansion under rising food demand has resulted in over half of global wetland loss, yet the flood risks faced by wetland-reclaimed croplands (WRCs) remain poorly understood. Focusing on China, a major grain-producing country with extensive wetland resources, we found that wetland reclamation converted 4818 km2 of wetlands into croplands, accounting for 35% of total wetland loss from 2000 to 2020, with pronounced concentrations in Northeast China. Flood occurrence also exhibited strong spatial heterogeneity: the middle Yangtze River and Northeast China both had high baseline frequencies, but trends diverged, with 80% of pixels showing positive slopes in the former and 73% showing negative slopes in the latter. More than 70% of WRCs were located in flood-prone regions, nearly 90% had experienced at least one flood event, and over half showed increasing flood frequency. A further counterfactual analysis showed that WRCs experienced higher flood frequency relative to matched non-reclaimed areas, suggesting a potential amplification of flood risks by wetland reclamation. These findings reveal substantial flood-related sustainability challenges for cropland expansion through wetland reclamation and underscore the urgent need to reconcile food security with wetland conservation.