## 5 Discussion and Conclusions
### Discussion
The Return Grazing Land to Grass project and \"black soil beach\" management (\"black soil beach\" means bare soil formed after degradation of alpine meadows [40]) have been helpful in vegetation growth and increasing forage yield; ecological migration [41] and the Livestock-Reduction project have helped reduce the livestock number, which has promoted the increase of grassland coverage; combating desertification has helped promote the sand-fixing capacity of vegetation and inhibit the expansion of the desert; human-induced rainfall has increased the lake and wetland area and the river runoff, mainly in the headwaters of the Yellow River. In summary, because of the lower elevation and a warm-wet climate, vegetation coverage and the wet- and marshland area in the headwaters of the Yellow River were much greater than those in the headwaters of the Yangtze River. In the headwaters of the Yangtze River, from the late 1970s to early 1990s, both a cold-dry type of climate and excessive grazing pressure caused a shrinkage in wet- and marshland and desertification; after the early 1990s, when the temperature and precipitation clearly started to increase, the LULC changed with an expansion in the wet- and marshland resulting from the conversion of desert. This change continued after 2004 with the melting of glaciers and snow covers, and the positive effects of the projects. In the headwaters of the Yellow River, during the late 1970s to 2004, a warm-dry climate and an excessive grazing pressure caused desertification, a decrease in the grassland coverage and wet- and marshland area; after 2004, an increase in precipitation, a reduced grazing pressure and the implementation of various projects all contributed to the increase of grassland coverage and expansion of wet- and marshland. Because of the constraints of climate and topography, the ecosystem in the headwaters of the Yangtze River is more fragile than in the headwaters of the Yellow River. In addition, the project implementation intensity in the headwaters of the Yangtze River was weaker than in the headwaters of the Yellow River; therefore, the LULC change in the headwaters of the Yangtze River was not as dramatic as in the headwaters of the Yellow River. The findings of our research showed that the LULC in the Tuotuo River basin changed in a positive way from the early 1990s with expansion of grassland and wet- and marshland area, a result that was different from other research that has considered that the positive change starting from 2004 onward. The reason for this assumption was that their study areas included the entire Yangtze River source region or the TRHR, which would obscure the particularity of the Tuotuo River basin. The Tuotuo River basin, located at the eastern foot of Tanggula Mountains, was widely spread with  
Figure 8: The annual livestock units in the headwaters of the Yellow River from 1988 to 2012.  
glaciers and mountains of snow. With the ongoing accelerated warming and glacier retreat, more water will be supplied to the Tuotuo River, which is a glacier-fed river [42]. According to runoff data from the Tuotuo River hydrological stations, during the period of 1975-2011, the annual average runoff was 0.91 billion m\({}^{3}\), showing an upward trend of 0.27 m\({}^{3}\)/a; during the period of 1997-2004, the annual average runoff was 1.17 billion m\({}^{3}\), showing an upward trend of 0.52 m\({}^{3}\)/a; after 2004, the water supply capacity of the river continuously increased, with the annual average runoff being 1.31 billion m\({}^{3}\), showing an upward trend of 0.91 m\({}^{3}\)/a. Compared to the period of 1997-2004, the runoff increased by 12.0% after 2004. According to the monthly data for the period of 1975-2011, the runoff in flood season accounted for 96.8% of the total annual runoff, especially in August. All these data showed that temperature is an important factor influencing the change in the Tuotuo River runoff.