A Comparative Overview of the Transversal Connectivity of Natural Landscape Mosaics to Freshwaters in the Metropolitan Areas of Berlin, London, & Paris

Connectivity among blue-green infrastructure (BGI) is a vital condition for enhanced ecosystem services provision in metropolitan regions where the social-ecological systems are interwoven. In this study, we conduct a comparative spatial assessment of transversal connectivity of natural surfaces to freshwater sources for the metropolitan areas of Berlin, London, and Paris. We focus on the transversal connectivity, which describes the lateral connection between natural surfaces and water surfaces, as opposed to connections along a water surface geometry. Initially, we compare the distribution ratios of water surfaces, natural lands, and transportation network at both the metropolitan and the urban level, relying on the Urban Atlas (UA) land-use and land-cover data. Our results show that at metropolitan level, Berlin has higher shares of water and natural surfaces (2.6 % and 40.1%) compared to London (1.32 % and 13.4 %) and Paris (0.9 % and 23.1 %). On the contrary, the transportation network covers less surfaces in Berlin (2.00 %) than in London (4.71 %) and Paris (3.62 %). Second, we investigate the connectivity among BGI elements, and most importantly, to the water surfaces. We considered the water surfaces as pivot elements in the landscape, while investigating the connectivity of natural areas to them. As part of the methodology, the transportation network is introduced in the analysis as the main fragmenting geometry. Our results show that in all three cases, more than 80 % of natural surfaces patches had no connection to freshwaters. Among them, the natural surface patches of Berlin record the highest level of transversal connectivity to freshwaters (17 %) On the other hand, London leads the ranking on the water surfaces that are not connected to any natural surface (>60 %). Transversal connectivity can be greatly increased with minor adjustments in spatial planning. For example, in Berlin the percentage of natural surfaces connected to freshwater jumps from 18% to 53%, if we assume that natural areas that are no more than 32 m apart can be connected in a network. This socalled potential transversal connectivity reveals areas where the connectivity among BGI is improvable and can enhance the capacities for nature-based solutions against emerging metropolitan challenges.