Abstract
China has become the largest contributing country to global vegetation regreening. However, the regreening pattern and subsequent impact on arid areas have not been comprehensively evaluated. Therefore, we selected the Loess Plateau, a representative arid region that has undergone evident vegetation restoration, to investigate the spatial patterns and temporal trends, as well as the drivers of vegetation change. This study primarily focused on 12 afforested watersheds during 2000–2018. Furthermore, both the impacts of vegetation regreening on runoff for the past two decades and the future projections were quantified based on the fraction of photosynthetically active radiation (fPAR), the Budyko model, and the global climate models (GCMs). fPAR for the last two decades indicates that vegetation in the Loess Plateau has experienced a continuous increasing trend during the growing season, primarily in response to the implementation of the Grain for Green Project (GFGP). Of the 12 watersheds, 9 experienced significant fPAR change with a change rate above 50%, and 11 exhibited a significant increase (p < 0.05) in runoff sensitivity to vegetation regreening, which indicates that vegetation regreening plays an increasingly important role in controlling runoff variation. The decline in runoff caused by vegetation regreening was particularly noticeable before 2011 or 2012; afterwards, runoff tended to vary with precipitation. In the future (2020–2049 and 2050–2099), decrease in runoff by regreening will be limited, as runoff is anticipated to decrease by 3.5% in 2020–2049 and 4.1% in 2050–2099 with a 20% increase in fPAR. These results indicate that runoff tends to be stable even with continuous vegetation regreening. While the reduction of runoff by regreening will be limited in the future, rapid human-induced vegetation regreening may aggravate water scarcity when flash droughts occur and may result in disasters in water-limited regions to the socio-economic stability and agriculture. Our study will provide an applicable theoretical foundation for water resources decision-making and ecological restoration.
Highlights
The Loess Plateau is located in northern China’s semi-arid and semi-humid climate transition zone
The annual mean fraction of photosynthetically active radiation (f PAR) in the 12 watersheds follows the pattern of the Loess Plateau: larger f PAR watershed values in the southeast regions (Watersheds 9–13), while lower f PAR values were found in the northwest regions (Watersheds 1–6)
Using the f PAR, water-energy balance model, and global climate models (GCMs)’ climate change, we quantitatively assessed the responses of the hydrological cycle to vegetation regreening throughout 12 watersheds of the Loess Plateau in both the past and future
Summary
The Loess Plateau is located in northern China’s semi-arid and semi-humid climate transition zone. Wind-deposited loess soils, low vegetation coverage, Forests 2019, 10, 906; doi:10.3390/f10100906 www.mdpi.com/journal/forests. In an attempt to address this ecological issue, over the past decade, the central government of China has adopted numerous soil conservation strategies including terraces, check dams, reservoirs, and reforestation [3,4]. The most famous one is the Grain for Green Project (GFGP), which has been implemented since 1999 and is the largest regreening or reforestation project worldwide [5]. Despite the effectiveness of the GFGP’s measures in controlling soil erosion and ecological degradation, their mitigation methods sharply reduced the observed runoff and induced a freshwater deficit in this eco-fragile area [1,6].
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