GIS-based Multi-criteria Decision Analysis for the Suitability Mapping of Nature-based Solutions (NbS) in the Mediterranean Eco-region

Abstract

The growing environmental risks induced by interacting climate-related and human-induced pressures threaten the survival and growth of different terrestrial and marine coastal ecosystems (MCEs). Climate adaptation and mitigation measures are required against this complex interplay to cope with resulting impacts jeopardizing the health and resilience of ecosystems and the services they provide. Nature-based solutions (NbS), consisting of ecosystem-based approaches, have gained increased attention as a tool for climate adaptation and mitigation that can increase biodiversity and provide benefit to people. Even though there is wider knowledge on NbS in the terrestrial environment in the state-of-the-art, experience on NbS design and implementation in MCEs is limited. In the specific context of marine coastal environment, restoration measures and transplantation of MCEs such as seagrass meadows and mangroves, are the most applied NbS. They contribute to climate regulation by sequestering carbon, while improving water quality thanks to their denitrification and sediment trapping potential and contributing to disaster risk reduction by providing services such as coastal protection and flood control. Identifying suitable environmental conditions for the effective implementation of NbS in marine coastal areas represents a key priority to drive more robust and cost-effective nature-based adaptation pathways. Drawing on this need, this thesis aims to develop a GIS-based NbS suitability model allowing to identify proper areas for NbS mainstreaming, with a specific focus on seagrass meadows in the Mediterranean Sea. Multi-criteria decision analysis (MCDA) and Analytic Hierarchy Process (AHP) are applied for data integration and variable prioritization. Different environmental variables are integrated, including climatic (e.g., sea surface temperature, thermal stress), water quality (e.g., salinity, nutrient concentration) and geomorphological (e.g., bathymetry, substrate type) ones. Moreover, suitability classes are identified for the selected environmental indicators based on an in-depth statistical approach leveraging multiple open-source web-data portals for the Mediterranean basin (e.g., Copernicus Marine Environment Monitoring Service). By using weights derived from pairwise comparison matrices based on expert judgement, suitability maps for climate, water quality and geomorphology are obtained for the Mediterranean case. Suitability maps and related statistics are obtained for the Mediterranean shallow waters identifying a large less suitable area in the northern Adriatic Sea in terms of water quality score. On the other hand, the coasts of Egypt and eastern Tunisia in the southern Mediterranean reported lower scores in terms of climate suitability. This thesis represents a first attempt to evaluate eco-regional scale NbS suitability for seagrasses in the Mediterranean Sea, using both climate, water quality and geomorphological parameters. Socio-economic and governance-related indicators should be integrated as well within the obtained environmental suitability thus, paving the way for a more complex multi-tier and multi-scale approach supporting detailed analysis and targeted interventions.