Regionalized Shared Socioeconomic Pathways: narratives and spatial population projections for the Mediterranean coastal zone

Existing narratives and population projections of the global-scale Shared Socioeconomic Pathways (SSPs) do not capture regional differences in socioeconomic development in the Mediterranean region. In this study, we regionalize the global SSPs to account for differences in coastal population development between northern, eastern, and southern countries of the region. First, we develop coastal SSP narratives that include region-specific elements and differentiate between geographical regions. Based on these narratives, we derive coastal population growth rates that vary for each SSP as well as between coastal, inland, rural, and urban areas. We apply these growth assumptions to observed population growth patterns in a spatially explicit manner. The Mediterranean coastal SSPs thereby reflect socioeconomic development patterns across countries as well as coastal versus inland development within countries. Our results show that coastal population in the Mediterranean increases across SSPs 2-5 by 3% to 130% until 2100 except for SSP1, where population declines by almost 20% compared to 2010. We observe considerable differences between geographical regions and countries. In the Mediterranean north, coastal population declines in SSP1, SSP3, and SSP4 and experiences the highest increase of more than 100% in SSP5. In southern and eastern Mediterranean countries, the highest increase in coastal population takes place in SSP3 and amounts to almost 180% by 2100. The regionalized SSP narratives and population projections are intended for assessing future exposure, vulnerability, and impacts of population to coastal hazards and sea-level rise but can also be of use for a wider range of Impact, Adaptation, and Vulnerability (IAV) studies.