Identification Of Impacts Of Climate Change And Human Activities On Sediment Change Of The Yellow River

The water and sediment variation in the Yellow River basin, especially in themiddle reaches, is a crucial factor that dominates the evolution of the Yellow Riverdelta. Both the climate change and human activities are affecting the sediment invarious ways. Thus, it is significant to identify their contributions to sedimentdecrease so that better understanding on the drainage system change and deltaevolution tendency would be feasible in the context of global change. Based onmeasured monthly/yearly datasets including precipitation, water discharge andsediment load from the main gauging stations during the period of1951-2011,analysis of the upper and middle reaches of the Yellow River basin by hydrology andcontrast analysis methods were presented at different phases with varying intensity ofhuman activities to illustrate the contributions of climate change and human activitieson the changing sediment load from the Yellow River. Statistical model(Precipitation-Sediment load) in base phase was built to estimate the theoreticalsediment load of the following phases in flood seasons. Compared with measured data,we could figure out the contributions to sediment decrease by climate change andhuman activities separately and quantitatively. The main conclusions are as follows:1. The sediment yield rates in four phases (1951-1968,1969-1986,1987-2001,2002-2011) of Lanzhou station(in upper reaches of Yellow River) in flood seasons are97.12%,98.11%,96.83%,94.53%. Statistical model (Precipitation-Sediment load) inbase phase was built, illustrating that anthropogenic activities contributed increasinglyto the sediment decreases, which increased by83.63%the recent10years(2002-2011). Eventually, human activities became the dominant factor on thesediment yield in the upper reaches of Yellow River.2. In the middle reaches of Yellow River basin, precipitation data was weighted by that of adjacent main gauging stations. The measured datasets of precipitation andsediment load demonstrate the sediment yield rates of flood seasons（May toSeptember） in four phases(1951-1968,1969-1986,1987-1999,2000-2011) are80.97%、78.04%、89.31%、97.42%. Statistical model (Precipitation-Sediment load)in base phase was built. According to this, anthropogenic activities contributedincreasingly to the sediment decreases. In particularly, the sediment load in middlereaches has been basically dominated by human activities (e.g., the XiaolangdiReservoir) in2000-2011, while climate change contributed for less than5%at thesame time.The results indicate that the Yellow River drainage system has been reversedseverely in the past60years. The variation of sediment is mainly controlled by humanactivities now rather than by nature. As a result, the clipping sediment decreases leadto radical change of the Yellow River delta.