Decomposing Long-Term Land-Use Contributions to Relative Runoff Potential Across Five Sub-Catchments in the Kameoka Basin, Japan

Simultaneous land-use changes can reinforce or offset one another, so urban expansion alone may not explain changes in catchment-scale runoff potential. This study examined long-term changes in land-use composition and in estimated relative runoff potential across five sub-catchments in the Kameoka Basin, Japan. Land use at eight time points spanning approximately 130 years (1890s–2021) was reconstructed from Meiji-period historical topographic maps and Land-Use Subdivision Mesh Data. The area-weighted runoff coefficient (C¯), derived from land-use-specific coefficients assigned with reference to Japanese technical standards and area proportions rather than observed rainfall–runoff data, was used as a proxy for relative runoff potential. Its change was decomposed into land-use contributions summarized as Net ∆C¯, total absolute contribution (Gross), and the net-to-gross ratio, complemented by interval-by-interval, transition-based, and coefficient-sensitivity analyses. Urban land increased by 5.1–16.0 percentage points, whereas Net ∆C¯ ranged from −0.004 to +0.037. Three contrasting contribution patterns were observed: structural inertia in Nanatani, dynamic offset in Chiji and Inukai, and development-driven increases in Toshitani and Sogadani. These contrasts remained identifiable under plausible alternative coefficients, although offsetting in Sogadani was more coefficient-sensitive. The approach may provide a diagnostic basis for differentiated sub-catchment-scale land management.