Since (1) 1927, the lower reaches of the Yellow River have been frequently cut off. The natural reasons are: the seasonal distribution of precipitation in the Yellow River basin is uneven, with less precipitation in winter and spring and less water entering the river; The lower reaches of the Yellow River are aboveground rivers, with no tributaries flowing in and almost no groundwater recharge. There is a strong dry wind and a large evaporation in the north. Man-made reasons: there is more water intake in urban and rural areas along the upper and middle reaches, so there is little water flowing into the lower reaches.
(2) The middle reaches of the Yellow River cross the Loess Plateau with loose soil and sparse vegetation. Under the scouring of summer rainstorm, the soil and water loss in the Loess Plateau is serious, and tributaries such as Dinghe River, Fenhe River and Weihe River flow into it. With the continuous increase of discharge, the sediment concentration in the river also rises sharply. Nearly 90% of the sediment entering the Yellow River comes from the middle reaches.
So, the answer is: Why is the lower Yellow River cut off? What is the reason for the high sediment concentration in the Yellow River?