黄土高原清水河流域土地利用/覆盖和降雨变化对侵蚀产沙的影响

近50 a来,在气候变化和生态恢复与治理工程实施的背景下,黄土高原的侵蚀产沙特征发生了明显的变化。以黄土高原典型中尺度流域清水河流域(面积436 km2)为研究对象,利用1959、1986、2007年的土地利用解译结果和1960—2005年该流域实测输沙和降水资料,采用非参数Mann-Kendall趋势分析法和滑动t检验法研究了该流域年输沙量、降雨量的变化趋势和突变点,并与通用土壤流失方程相结合分析了该流域土地利用和降雨变化对输沙量变化的贡献率。结果表明:该流域年输沙量47 a间有显著的下降趋势,突变点位于1980年;降雨量没有明显的趋势性变化,极端降雨指数下降。降雨因素对输沙量减少的贡献率为9.89%,土地利用的贡献率为90.11%,土地利用变化中工程措施淤地坝的贡献率为5.56%,植被变化的贡献率为84.55%。该流域47 a间乔木林地面积增加了944.27%,灌木林地增加了19.33%,表明清水河流域林地面积增加是导致输沙量减少的主要原因。

Effects of Precipitation and Land Use/Cover Variability on Erosion and Sediment Yield in Qingshuihe Watershed on the Loess Plateau, China

Large scale re-vegetation based soil and water conservation deployed to combat the severe soil erosion since the 1950s on the Loess Plateau of China has resulted in the dramatic change of land use and land cover. On the other hand, the region is considered to be the most sensitive area for global climate variability. Therefore, it is critically important to understand and predict the coupling effects of land use and climate variability on the sediment characteristics for integrated watershed management and ecological restoration. The study examined the trend of annual sediment, precipitation and their change points for a typical meso-scale Qingshuihe watershed located on the Loess Plateau by using non-parametric Mann-Kendall test, Moving t-test technique, and hopped parameter analysis. Based on the land use/cover of 1959, 1986 and 2005, USLE was used to separate the land use/cover change effects on the sediment yields from that of climate variability. The result showed that during the 47 a of 1960-2005 the annual sediment yield had significant decreasing trend,change point occurred in 1980. Precipitation had no significant trend, but the indexes of extreme precipitation decreased. It was estimated that the precipitation changes accounted for 9.89％ and land use/cover changes accounted for 90.11%, among which 5.56% from the engineering measure(check dams) and 84.55% from vegetation changes to the reduction sediment yield of Qingshuihe watershed. According to the analytical result of land use, in 1959-2005 the forest area increased 944.27% and the shrubbery area increased 19.33%. So, the increase of forest land areas is the main reason to give rise to the decrease of sediment yield in the Qingshuihe wastershed.