Estimating the maximum vegetation coverage and productivity capacity supported by rainwater resources on the Loess Plateau

Abstract

Large-scale anthropogenic revegetation brings new challenges by enhancing water consumptions in non-humid regions, even if it improves ecosystems. Water resources in water-stressed areas are primarily provided by precipitation, and excessive afforestation can potentially lead to severe imbalance between water supply and demand due to limited rainwater resources. Therefore, it is essential to evaluate the maximum vegetation coverage and productivity capacity supported by rainwater resources. In this study, the sustainability of revegetation was characterized by calculating the upper limit of vegetation leaf area index (LAI) supported by rainwater resources. The carbon sequestration capacity and efficiency of the maximum and the actual vegetation scenario were compared over the Loess Plateau (LP), which is well known as a region experiencing both large-scale vegetation restoration and severe water shortages. The upper limit on LAI was calculated based on evapotranspiration (ET) supported by rainwater resources, using the Shuttleworth-Wallace (S-W) model optimized in this study by adding dynamic vegetation and carbon dioxide components. The carbon sequestration capacity and efficiency of vegetation under different restoration scenarios were estimated in an analytical water use efficiency (WUE) model. Both the models perform well and are consistent with observations. The results show that the LAI of the maximum vegetation scenario is 11.5% higher than the actual scenario if vegetation on the LP is restored to its maximum level. The average gross primary productivity under the maximum vegetation scenario is 25.0% higher than the actual scenario, while the ecosystem WUE will increase by 17.9%. It should be noticed that the maximum scenario is a theoretical upper limit based on ideal assumptions. Our findings reveal that improving rainwater utilization efficiency can further develop the potential of sustainable vegetation restoration while improve its efficiency, and will provide guidance and theoretical support for vegetation restoration planning on water-scarce regions.