Satellite observations reveal carbon gains and water resource pressures associated with the grain for green program on the Chinese Loess Plateau

It has been more than 20 years since the ‘Grain for Green’ program (GGP) implementation by the Chinese government. While numerous studies have examined land surface changes and their environmental impacts following the GGP, a comprehensive assessment of its integrated eco-environmental effects—spanning vegetation dynamics, carbon sequestration, and water resource—remains lacking. In this study, we integrate a suite of state-of-the-art satellite-based products and ground observations to quantify the spatiotemporal changes in vegetation growth and productivity, carbon sequestration, and water availability associated with the implementation of the GGP across the Loess Plateau. Our results indicate a significant expansion in forest cover from 2000 to 2015, with a relative increase of 53.2%, which was closely associated with the implementation of the GGP. Consequently, vegetation growth, as reflected by the normalized difference vegetation index and vegetation optical depth, showed marked improvement across the region. Substantial gains in carbon sequestration and storage were also observed during the GGP implementation period, with aboveground biomass carbon increasing by 24.4%. Regarding water resources, remotely sensed evapotranspiration showed a modest increase, whereas surface soil moisture remained relatively stable, likely due to an upward trend in precipitation. In contrast, river runoff and terrestrial water storage anomaly declined markedly. Further analysis suggests that enhanced evapotranspiration associated with afforestation under the GGP may have contributed to the observed runoff reduction, although other factors, including agricultural irrigation and socioeconomic development, may also have influenced these hydrological changes. Overall, the implementation of GGP was associated with significant greening and strengthened carbon sinks in this semi-arid region, yet it has concurrently imposed pressure on local water resources. These findings highlight that large-scale afforestation represents a double-edged sword, highlighting the importance of carefully considering water-resource constraints in future ecological restoration efforts to avoid unintended hydrological consequences.