*2.1.4 Uncertainty*

As a result of subjective and objective reasons, the impact of reservoir removal is uncertain. The subjective reason is that relevant researches are not in-depth and comprehensive enough, and many problems are difficult to be accurately explained from the mechanism. For example, there are still many disputes about the evolution process and mechanism of river channel in the reservoir caused by sediment output, and how to scientifically determine the goal of ecosystem restoration after dam removal is still an academic problem. The objective reason is mainly the impact of global climate change, which is also a difficult problem faced by all water resource management activities.
