Directional policy alignment in water resources carrying capacity for sustainable city futures in drylands

Sustainable city futures in drylands are increasingly constrained by hard water resource limits under climate change, city expansion, and low-carbon transition. Water resources carrying capacity (WRCC) is not only an indicator of water security, but also a diagnostic tool for identifying development boundaries, policy-deviation risks, and adaptive governance priorities. Existing WRCC studies, however, mainly focus on historical assessment or trend prediction, with limited attention to translating policy objectives, city functional suitability, and prediction–policy deviations into computable indicator-level constraints. Taking 12 cities in the Qilian Mountains region of Northwest China as an empirical case, this study develops a policy-aligned framework for future WRCC projection and diagnosis. The framework embeds policy objectives into a data-driven prediction chain to evaluate whether future city development pathways align with water security, low-carbon transition, and adaptive governance targets. Results show that regional WRCC increased from 0.43 to 0.50 during 2000–2023, while the water resources subsystem remained weak, indicating that natural water endowments and supply–demand patterns remain the fundamental boundary for sustainable city transformation. For 2030–2050, 71.25% of city–indicator combinations were highly or broadly consistent with policy orientations, but per capita carbon dioxide emissions, per capita domestic water consumption, per capita water consumption, and water supply modulus showed policy-deviation risks. Following bounded policy-alignment correction of the projected indicators, regional WRCC was 0.52 in 2030 and 0.54 in both 2040 and 2050. The limited increase after 2040 indicates that future carrying-capacity improvement remains constrained by rigid water resource boundaries and inter-city structural differences. Indicator contribution decomposition reveals a shift in WRCC drivers from resource endowments, population distribution, and development foundations toward water-use efficiency, pollution control, low-carbon transition, and ecological restoration. This study reframes WRCC as a directional policy-alignment diagnostic framework for water-constrained city planning, risk identification, and adaptive governance in dryland cities.