Spatial scale effects on the response strength of water resources supply-demand balance to driving factors

• Analyzing the spatiotemporal dynamics of the water supply–demand balance across scales. • Water yield is more strongly correlated with natural factors at the sub-basin scale. • Driving factors have a smaller impact on water supply than demand. • Guiding water resource management practices through multi-scale analysis. Amidst escalating global climate change and intensifying anthropogenic activities, the imbalance between water supply and demand has become a critical sustainability challenge. Nevertheless, our understanding of the spatiotemporal heterogeneity in the water resources supply–demand balance is limited, particularly regarding scale-dependent responses of driving factors. Therefore, this study adopts a geographical perspective, focusing on the Haihe River Basin — an internationally recognized water-scarce region. By integrating machine learning and GIS spatial analysis techniques, it reveals the multi-scale spatial relationships and mechanisms between various factors, including natural and socio-economic ones, in the water resources supply–demand system, from the aspects of feature importance, variable correlation, and spatial heterogeneity. The results show that the Haihe River Basin faces severe water shortages. Compared to localized water shortages at finer scales (grid scale), regional average water scarcity is more pronounced at coarser scales (sub-basin and city scales), suggesting that management strategies based on a single scale may have limited applicability. Additionally, the response of water supply and demand to driving factors exhibits uncertainty influenced by spatial scale. Specifically, the correlation between water supply and natural factors such as precipitation and slope is stronger at the sub-basin scale than at the city scale. As for water demand, at the city scale, factors with strong correlations become more pronounced, with human factors having a greater influence on water demand. The effect scale of influencing factors on water supply is smaller, while the effect scale on water demand is larger. Topographic factors such as elevation and slope show significant spatial heterogeneity in water demand, whereas climatic and vegetation factors exhibit pronounced spatial heterogeneity in water supply. Natural geographical factors tend to exhibit smaller effect scales.