Irrigation accelerated vegetation greening in China

China is one of the regions with the most significant vegetation greening. Previous studies generally attribute this change to climate change and broad human activities. However, given China’s large irrigation water use, the role of irrigation-related water supply in vegetation greening remains insufficiently evaluated. Existing studies have paid limited attention to the irrigation water cost associated with greening and vegetation responses under precipitation-irrigation coupling scenarios, leaving the water-use cost and regional differences in irrigation-related effects unclear. Based on 1982–2022 growing-season data, this study analyzes long-term changes in fractional vegetation cover (FVC), climate factors, and irrigation water across China and four climate zones. It evaluates the irrigation-related effects from three perspectives: a vegetation-precipitation-irrigation coupling zoning and classification framework for identifying vegetation responses under different water-supply combination scenarios; irrigation water cost per unit vegetation greening for characterizing water-resource inputs; and a two-stage residual attribution model for estimating irrigation-related contribution to vegetation greening after controlling for climate factors. The results show that: (1) Growing-season FVC in China increased significantly from 1982 to 2022, at 0.91%/decade, and areas with significant greening accounted for 56.11%. Irrigated areas showed a higher greening rate than non-irrigated areas; areas with increased irrigation had a greening rate approximately twice that of non-irrigated areas, indicating a close association between irrigation-related water supply and vegetation improvement. (2) The irrigation water cost per unit vegetation greening differed markedly among climate zones, with relatively low costs in the semi-arid zone but higher costs in the arid zone and some high-intensity irrigation areas, suggesting significant water-resource constraints. (3) In irrigated areas with a greening trend, the climate-factor, irrigation-related, and unexplained residual contributions to vegetation greening were 48.67%, 25.09% and 26.24%, respectively, indicating that climate factors remain the dominant explanatory component, while irrigation also plays a non-negligible role. This study may inform ecological restoration and agricultural water-resource allocation.