Hydrological rhythm refers to the periodic and rhythmic changes of lake water regime. The generalized hydrological rhythm includes circadian, monthly, seasonal and interannual rhythms. Under normal circumstances, due to factors such as watershed climate and underlying surface, it is relatively stable. The multi-year average water level of the lake tends to be stable, that is, the normal annual average water level of the lake is relatively stable. The circadian rhythm has little impact on the ecosystem. Therefore, the narrow hydrological rhythm refers to the monthly and seasonal rhythm.
The water surface area of Poyang Lake continues to shrink due to the dual effects of continuous reduction of rainfall and water inflow relates to hydrological rhythm in a narrow sense according to the above definition.