Abstract:The continuous ecological management of the Loess Plateau is known throughout the world for two strategies: the integrated soil conservation project that began in the 1970s, and the "Grain for Green" project that began in the 1990s. Six sub-catchments nested in the Beiluo River basin were selected to investigate streamflow regime variations during the two project periods. The annual streamflow trends and change points were detected using a bootstrap-based Mann-Kendall test and Pettitt test. Annual streamflow (from the 1950s to 2011) exhibited significantly negative trends in five out of six catchments, varying from´0.15 to´0.30 mm/a. During the integrated soil conservation period, the annual streamflow was reduced due to high flow decreases (5% of time exceeded), whereas in the low flows (95%) it increased in all sub-catchments. During the "Grain for Green" period, the annual streamflow decreased due to daily streamflow reductions at four stations. In addition to high flow and low flow decreases at the Wuqi and Liujiahe stations during the "Grain for Green" period, it is significant that the low flows continuously increased. Compared with trends from the forestry area, which includes the Zhangcunyi and Huangling stations, incremental annual streamflow reductions were observed in other sub-catchments, which can be linked to ecological management. This result implies that streamflow can be moderated by appropriate management options, even in semiarid areas. It was concluded that a stable streamflow regime can be achieved in vegetated areas, and streamflow moderation is dependent on ecological management practices.
The variability of baseflow is a comprehensive reflection of land use/cover changes (LUCC) and an important hydrological characteristic considered in maintaining sustainable development of an ecosystem. Daily streamflow data from 1959 to 2005 at Wenjiachuan gauge station in Kuye catchment on the Loess Plateau were used to analyze baseflow responses to the LUCC. Chapman-Maxwell digital filter was used to separate daily streamflow into baseflow and surface flow. Both nonparametric Mann-Kendall test and Pettitt test were adopted to detect the trend of the baseflow and identify its change point. Double mass curves method was also employed to verify the change points. Results are as follows: (1) The average annual baseflow in Kuye catchment was 24.7 mm, accounting for 38% of total runoff. A significantly negative trend of the annual baseflow was detected in the last 50 years. The average change rate was 0.628 mm.a-1 , which was about 2.5% of the average annual baseflow. Two change points occurred in the years of 1980 and 1996. (2) Baseflow regimes, as represented by daily baseflow curves, showed an increasingly dramatic reduction across the high, median and low percentiles of the time and an increase of zero-baseflow days in the catchment. The variability of baseflow represented by baseflow duration curves increased period by period. (3) By considering statistical insignificance detected in annual precipitation, the change of baseflow in Kuye catchment was greatly related to soil conservation measures implemented from the 1970s to 1980s and coal mining development after 1996.
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