Scaling laws of irrigation networks in China rice polder communities

Irrigation networks are core infrastructure for agricultural systems, yet their cross-scale variation in spatial structures and infrastructure returns remains elusive. This study develops a scaling-law framework for examining irrigation networks in Chinese rice-polder communities. Using historical and contemporary satellite imagery, we digitize irrigation networks and rural houses in the Yangtze River Delta Polders and Dongting Lake Plain Polders in the 1970s and 2020 s, and derive geometric, topological, fractal, and allometric indicators. The results show that canal length scales approximately linearly with community area, indicating that rice-polder irrigation networks do not exhibit the economies of scale commonly observed in urban infrastructure networks. This linear scaling is associated with a mixed dendritic-homogeneous structure, in which higher-level canals exhibit a branching pattern while terminal canals form relatively homogeneous, interconnected local networks. The topological and fractal analyses further show that irrigation networks are functionally decentralized and moderately space-filling, suggesting that multiple water gates and interconnected canals enhance water accessibility, drainage flexibility, and resilience to blockage. Furthermore, the allometric relationship between the scales of irrigation networks and households suggests that irrigation investment has shifted from involution to de-involution growth over the past 50 years in rice polders in China. These findings extend the scaling-law framework to agricultural irrigation systems and provide quantitative insights for irrigation network planning, canal density management, and farmland consolidation in rice polder regions.