Hydrological connectivity moderates seasonal river warming in the Yangtze River Delta: Evidence from a decade of Landsat observations

River surface temperature (RST) plays a crucial role in shaping river thermal regimes and ecosystem functioning, yet seasonal and reach-scale factors influencing RST remain poorly understood. Here, we derive reach-scale RST for the Yangtze River Delta (YRD) from Landsat imagery (2010-2020) using a novel river-width-adaptive sampling method (River Surface Moving Window, RS-MW). An Extreme Gradient Boosting (XGBoost) model, in conjunction with Shapley Additive Explanations (SHAP) and a hydrological connectivity (HC) metric, is used to quantify the seasonal influence of climatic, river-characteristic, topographic and riparian-environmental factors. The results indicate that RST in the YRD increased at an annual mean rate of 0.092 °C yr −1 from 2010 to 2020, with the most pronounced seasonal warming observed in spring and winter. RST displays strong spatial heterogeneity during spring and summer and a distinct north-south gradient in autumn and winter. Climatic factors exert the strongest overall control on RST, followed by river-characteristic factors, which play a key role in shaping spatial heterogeneity and seasonal modulation, whereas topographic and riparian-environmental factors are comparatively less influential. Air temperature (T a ) is identified as the dominant warming factor, while HC effectively mitigates elevated RST, particularly in warm seasons, with SHAP-based estimates indicating a cooling contribution of approximately 1.5 °C in spring and summer, but less than 0.6 °C in autumn and winter. Riparian vegetation contributes to cooling, whereas impervious surfaces intensify thermal stress. The proposed framework offers a transferable and fine-scale approach to RST monitoring to support climate-adaptation and water-management strategies. The findings highlight that restoration of hydrological connectivity and riparian vegetation are effective strategies for mitigating the future increase in RST, with additional measures such as wetland reconstruction and the development of blue-green infrastructure further enhancing river ecosystem resilience.