Beyond Tourism Intensity: Patterns of Infrastructure Buffering, Evidence Gaps, and Coastal Sustainability in Three Greek Island Destinations

Overtourism is often assessed through visitor intensity, although its effects also depend on infrastructure performance, resource demand, spatial development, and evidence availability. This study develops a comparative diagnostic framework and applies it to Mykonos, Patmos, and Spetses, representing three contrasting Greek island tourism models. Ten indicators were classified according to their analytical role. Seven indicators were scored within three dimensions—resource pressure, infrastructure system, and tourism demand—while coastal water quality was treated as environmental-state evidence and built-up and coastal development as descriptive spatial evidence. Evidence confidence was assessed separately. Sensitivity analysis included leave-one-indicator-out tests, omission of indicators based on shared tourism data, threshold variation, and alternative standardization. Mykonos recorded the highest resource-pressure (4.00) and tourism-demand (3.50) scores, together with extensive built-up and coastal development, but its centralized wastewater treatment system operated within reported compliance limits. Patmos recorded lower tourism pressure but documented wastewater treatment underperformance, while Spetses lacked centralized wastewater treatment and had important monitoring gaps. The Mykonos results are consistent with pressure-specific infrastructure buffering, although the available data do not support causal attribution. The framework provides a comparative diagnosis without producing a single overtourism score and helps identify areas where further monitoring and assessment are needed.