When Green Percentage Misleads: Population-Adjusted Stress and Leverage of Urban Green Connectivity in Seven European Cities

Abstract

Green-area comparisons based solely on percentage cover, patch count, and aggregated connectivity may understate the stress on green systems caused by their high population pressure, limited resident-level supply, fine-grained grain, concentration of connectivity, and water shortage in dry climates. For the current comparison, the Population adjusted Connectivity Stress and Leverage (PaCSL) is calculated for the cities of Almada, Antwerp, Lisbon, Paris, Poznan, Tartu, and Zurich. PaCSL includes five normalized stress indices: population pressure, supply of green areas per 1000 residents, UGA fine-grained morphology, dominance of large or highly connected patches, and climate-induced water constraints. A distinct leverage factor is calculated as the product of the connectivity intensity and the percentage of green area cover, thus allowing to separate stressed systems from those with high consolidation potential. As the comparison demonstrates, the green percentage measure is an insufficient criterion for evaluating green-network condition in cities. For instance, Paris and Lisbon both have 16\% green areas, yet in Paris there is a much smaller share of green area per 1000 inhabitants (0.80 ha) compared to Lisbon where this figure stands at 2.49 ha per 1000. Paris has the largest PaCS stress index (0.989) with its maximum population pressure, maximum green supply scarcity, near-maximum UGA grain stress, maximum dominance, and moderate water constraint. The second highest score belongs to Lisbon (0.522) primarily due to small amount of green space per 1000 residents and severe water constraint. The third position, with PaCSL scores of 0.377 and 0.350 respectively, is shared by Almada and Tartu; however, the two have vastly differing leverage values of 0.835 and 0.018. Zurich has the largest leverage score (1.000) corresponding to 30\% green coverage and 292.90 connectivity units per hectare.