Impact of vegetation restoration on hydrological processes in the middle reaches of the Yellow River, China |
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Authors: | Zhong-bao Xin Xin-xiao Yu |
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Institution: | Key Laboratory of Soil and Water Conservation and Desertification Combating of the Ministry of Education, Beijing Forest Univer-sity, 100083, P. R. China |
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Abstract: | Sediment discharge from the Yellow River originates mainly from the drainage area between Hekouzhen and Longmen, i.e., the
Helong area. Spatial-temporal variations of the vegetation cover in this area during the 1981–2007 period have been investigated
using GIMMS and SPOT VGT NDVI data. We have also analyzed the interannual variations in vegetation cover and changes in annual
runoff and sediment discharge, the consequences from precipitation change and the Grain for Green Project (GGP). The results
show that vegetation cover of the Helong area has increased during the 1981–2007 period. The northwestern part the Helong
area, where the flat sandy lands are covered by grass, has experienced the largest increase. The region where the vegetation
cover has declined is largely found in the southern and southeastern Helong area, which is a gullied hilly area or forested.
Although precipitation was relatively low during the 1999–2007 period, the vegetation cover showed a significant increase
in the Helong area, due to the implementation of the GGP. During this period, the most significant improvement in the vegetation
cover occurred mainly in the gullied hilly areas of the Loess Plateau, such as the drainage basins of the Kuyehe and Tuweihe
rivers and the middle and lower reaches of the Wudinghe and Yanhe rivers. A comparison of the average annual maximum NDVI
between the earlier (1998–2002) stage and the next five years (2003–2007) of the GGP indicates that the areas with increases
of 10% and 20% in NDVI account for 72.5% and 36.4% of the total area, respectively. Interannual variation of annual runoff
and sediment discharge shows a declining trend, especially since the 1980s, when the decrease became very obvious. Compared
with the 1950–1969 period, the average runoff during the 1980–2007 period was reduced by 34.8×108 m3 and the sediment discharge by 6.4×108 t, accounting for 49.4% and 64.9% of that in the 1950–1969 period, respectively. There is a positive correlation between
the annual maximum NDVI and annual runoff and sediment discharge. This correlation was reversed since the implementation of
the GGP in 1999 and vegetation cover in the Helong area has increased, associated with the decrease in runoff and sediment
discharge. Less precipitation has been an important factor driving the decrease in runoff and sediment discharge during 1999–2007.
However, restoration and improvement of the vegetation cover may also have played a significant role in accelerating the decrease
in annual runoff and sediment discharge by enhancing evapotranspiration and alleviating soil erosion. |
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Keywords: | middle reaches of the Yellow River Hekouzhen to Longmen area (Helong area) vegetation restoration Grain for Green Project (GGP) runoff and sediment |
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