Irrigation rationality: a behavioral account of rural settlement hierarchy

What encourages people to settle together in a hierarchical pattern in rural societies? Traditional accounts of settlement hierarchy, including central place theory and rank-size laws, are insufficient, as they overlook the productive rationality required for agricultural irrigation. In this study, we examine whether irrigation is associated with the hierarchical structure of rural settlements. We quantify their hierarchical structure using the rank-size distribution of over 2600 agrarian settlements that crop rice or wheat across rural China. Our findings indicate that rice-cropping settlements exhibit a less hierarchical structure than wheat-cropping settlements, consistent with differences in the spatial morphologies of their irrigation networks and housing distributions. Besides, the degree of irrigation dependence is systematically associated with variation in settlement hierarchy. Historical analyses over the past century further suggest that irrigation networks and settlements co-evolved in a coordinated but differentiated way: stable backbone canals supported the expansion of central settlements, while newly extended terminal canals were associated with the emergence of small peripheral settlements. These findings provide new evidence for the behavioral explanation of how agricultural irrigation affects the agricultural settlement hierarchy and effectively extend the productive principle to settlement theories.