Spatial and wavelet analysis of precipitation and river discharge during operation of the Three Gorges Dam, China

The Three Gorges Dam and Reservoir on the Yangtze River is one of the world's largest dams. After the dam's construction in 1997, the reservoir started filling up, expanding to a size of over 600 km2. Therefore, its possible influence on maintaining the size and water level of this waterbody is significant and concerning. This research utilized wavelet coherence analysis to examine the temporal correlation and phase coherence among various datasets, including dam injection (1998-2018) and discharge (2003-2018) data, ground station precipitation data along the Yangtze River (1998-2020), and river discharge raster maps 1998-2018. The analysis revealed a strong coherence between dam operation and river discharge rates, as well as a minor seasonal coherence between dam operation and precipitation. The periodic properties of the datasets indicate that, in addition to the general seasonal changes observed in the wavelet coherence analysis, other periodic signals in the datasets are also coherent over time. This coherence may be attributed to the simultaneous impacts of dam operation on precipitation and river discharge. The reasons for this coherence are still unknown, and further studies are required, incorporating information on soil moisture, groundwater levels, air humidity, and the monsoon, to understand how the dam affects them.