近50年黄土高原水土流失的时空变化

在降水变化和人类活动的影响下,近50a黄土高原水土流失发生了深刻变化.利用黄土高原115个水文站的输沙量数据和276个雨量站的降水数据,分析了近50a来黄土高原输沙强度的时空变化特征,并评估了降水变化对其影响.研究表明:近50a黄土高原输沙强度呈现明显下降趋势,尤其是自20世纪80年代以来,下降趋势非常显著.从水土保持措施实施前后两时期对比来看,黄土高原输沙强度整体呈现减弱态势,并存在明显的空间差异.输沙模数＞5000t/(km2·a)区域的输沙强度减弱明显,其面积较前期减少了44.3%.输沙强度减弱最为明显的区域位于无定河中下游以及山西中北部地区,输沙强度减少在40%以上.降水减少是近50a黄土高原输沙强度减弱的重要原因,它们时空变化格局在空间上一致.从黄河中游10条主要支流来看,人类活动对输沙量减少可能起主要作用,其贡献率在61%～93%之间.

Temporal and spatial variability of sediment yield on the Loess Plateau in the past 50 years

In the past 50 years, the sediment yields of the Loess Plateau have changed significantly, due to both natural and human factors. This study analyzes the temporal and spatial variability of sediment yields of the Loess Plateau, and estimates the effect of precipitation variability on sediment yield using the annual sediment yield. Data were collected from 115 hydrological and 276 meteorological stations. The 10 main tributaries of Middle Yellow River show that the annual sediment discharge has decrease over the past 50 years, especially since 1980s. Two periods were compared: one prior to the implementation of soil conservation methods (1956-1969), and one post-implementation (1970-1989). The sediment yield decreased by 44.3%; there are also significant spatial differences between the periods. The most significant decrease was observed the Middle and Lower Wudinghe River, and in the north central Shanxi Province, where sediment yield decreased by more than 40%. A similar pattern of decline was evident for precipitation records; therefore, precipitation variation might play an important role in the decrease in the sediment mobilization from the landscape, and hence, the decrease in sediment yields. However, human activities such as soil conservation and water diversion contributed significantly more to this decline in the sediment yield than the precipitation. It is estimated that 61%-90% of the decrease in sediment yield can be attributed to human activities.