Synergistic changes in river-lake runoff systems in the Yangtze River basin and their driving force differences

Climate change and human activities simultaneously alter river-lake relationships. Determining the dynamics of river-lake runoff systems on multiple time scales and their differences in response to driving forces can provide insights into hydrological processes and water resource management. This study investigates the synergistic evolution of river-lake runoff systems in the middle and lower reaches of the Yangtze River basin (MLYR) using the cross-wavelet transform method. The effects of different driving force changes on river-lake runoff regimes are quantified based on the Budyko hypothesis, and an InVEST model is developed to assess the spatial and temporal patterns of habitat quality. The results indicate that during the variation period, the runoff distributions of the Yangtze River-Dongting Lake and Yangtze River--Poyang Lake runoff systems are both skewed towards lower values in the flood seasons compared with those in the base period. The storage of lakes mitigates the extent of human disturbance to the mainstream hydrological regime, particularly under extremely low condi-tions. From 1960 to 2021, five significant resonance periods are indicated in the river-lake runoff system, and the phase-angle relationships indicate a positive phase coupling between the lake and mainstream hydrological regimes, with the lake lagging behind the mainstream; however, this interaction tends to weaken. In the mainstream and Dongting Lake basins, subsurface conditions are the dominant factor contributing to runoff variability, with contributions ranging from 50.9% to 72.6%; in the Poyang Lake basin, precipitation is the dominant factor, with a contribution of 50.6%; and in the Han River basin, changes in the potential evapo-transpiration contribute to 50.6% of runoff variability. The proportion of high habitat quality in the MLYR is approximately 52%, the Dongting and Poyang Lake basins indicate a high habitat quality rating. However, frequent human activity is the main reason of conversion from higher habitats to lower ones, which may result in wetland habitat degradation.