How Do Urban Network Externalities Affect Regional Economic Growth? Evidence and Heterogeneity Analysis from China’s Yangtze River Economic Belt

Urban network externalities have emerged as a novel impetus for regional economic growth. However, the extent to which inter-urban network connections promote regional economic growth and the associated spatiotemporal heterogeneity remain underexplored. This study constructs a multi-dimensional urban network framework from the perspectives of enterprise linkages, infrastructure connectivity, and innovation collaborations, capturing the multifaceted nature of intercity relationships and their critical role in shaping regional development. Utilizing the Cobb–Douglas production function and the spatial Durbin model, the study quantitatively assesses the impact of urban network externalities on economic growth and examines the spatiotemporal heterogeneity of these impacts. The main findings are as follows: Urban network externalities generally exert a positive influence on regional economic growth, yet this effect exhibits significant regional and city-size heterogeneity. Regions with more developed networks experience stronger growth effects from these externalities. Moreover, large cities benefit more substantially from network integration compared to small and medium-sized cities. Spatial decomposition of effects further reveals that urban network externalities promote economic growth through both local direct effects and spillover effects to neighboring areas. Approximately 70% of the economic growth contribution originates from direct effects within the region, while nearly 30% stems from spillover effects from adjacent regions. Additionally, the spatial spillover effects display clear distance decay, following an inverted U-shaped pattern with a bimodal distribution. Significant spillover effects are observed within 380 km, peaking at 180 km and 340 km.