Abstract

In this study Qiaozidong watershed and Qiaozixi watershed in third sub-region of Loess Plateau were selected as the case to investigate the effects of land-use/land-cover change on hydrological dynamics at watershed scale. The results showed that the impact of land use/land cover on annual runoff yield was significant. The runoff coefficient of controlled watershed reduced about 50%, 85%, 90% respectively in wet, normal and dry year in comparison with the runoff coefficient of uncontrolled watershed. The average runoff coefficient reduced 73.6% during the period of 1995-2004 compared to that in the previous period of 1986-1994 for land use in controlled watershed. And the impact of land use and vegetation changes on runoff strengthened in response to the increasing rainfall. In addition, the impacts of land use/land cover on runoff yield are characterized by seasonal fluctuation. The maximum monthly runoff reduction in both controlled watershed and uncontrolled watershed occurred in May, when was consistent with the period of the maximum land coverage appeared. And only in growing season obvious runoff yield difference was observed between the two land-use periods of controlled Qiaozidong watershed. Finally, the rainfall amount and rainfall intensity in 30 min had significant correlation with flood volume, and had greater impacts on flood volume in uncontrolled watershed than that in controlled watershed. When the rainfall intensity reached a certain threshold, the variance of flood peak in two paired watershed reduced, which showed that the effects of forest on flood weakened. At the same time, flood peak discharge frequencies indicated that peak discharge would respond to the land use and vegetation change obviously on condition that there were the same frequencies of rainfall intensity in the earlier and later periods.

Keywords: land use/land cover; hydrological dynamics; loess gullied-hilly region