Assessing Urban Development Capacity Under Water Constraints: A Planning - Oriented Index for Spatial Policy

Rapid urbanization and increasing pressure on water resources challenge the sustainability of conventional spatial planning practices. Traditional approaches, primarily based on functional zoning and post hoc infrastructure design, often neglect the dynamic relationship between urban development and water availability. This has led to overdevelopment in many regions — particularly coastal and tourism - intensive areas — where water demand exceeds supply capacity, resulting in resource stress and reduced system resilience. This study proposes a novel planning - oriented framework — the Urban Water Adequacy for Development Index (UWADI) — which integrates water resource constraints into the early stages of spatial planning. Unlike conventional assessments based on observed consumption, UWADI relies exclusively on planned development parameters, enabling prior evaluation of whether proposed urban growth is compatible with available water resources. The index is defined on a scale from 0 to 1 and consists of four components: Adequacy Deficit (AD), representing the balance between planned demand and available supply; Seasonal Exposure (SE), capturing peak demand variability; Resource Vulnerability (RV), reflecting the robustness of water sources; and Phasing Mismatch (PM), addressing the temporal alignment between infrastructure provision and development. The framework is grounded in integrated planning principles and aligned with European policy directives, including the Water Framework Directive. A structured workflow links spatial planning parameters with water resource assessments, allowing development proposals to be classified according to water adequacy thresholds and associated planning constraints. The results demonstrate that incorporating water availability as a binding constraint significantly improves the robustness and feasibility of spatial plans. The proposed UWADI framework provides a transparent and scalable tool for bridging the gap between hydrology and spatial planning, supporting more resilient, sustainable, and evidence - based urban development under increasing water stress.