Urban populations are increasingly moving into hazardous areas, which leads to widespread and frequent impacts from hazard events. Although these exposure trends have been quantified for other hazards, global exposure analyses for volcanic hazards remain limited. Here, we quantify global and regional changes in city exposure to volcanic hazards through time. With GHS-UCDB and GHS-POP datasets, we use spatio-temporal metrics to track urban expansion within 100 km of volcanoes active in the Holocene from 1975 to 2020, with projections to 2030. The number of cities within 100 km of volcanoes is projected to more than double, with populations increasing by 154%. The proportion of people within 100 km of volcanoes who live in cities increases from 44% (~186 million) in 1975 to over 50% by 2030 (~473 million). Exposed city populations concentrate within 20–30 km from volcanoes, and average urban population density generally decreases closer to volcanoes. Exposure growth is highest in Southeast Asia and East Africa. Most cities expand and densify, with many growing faster toward nearby volcanoes. Case studies show how urban expansion intersects with volcanic impact pathways. These trends indicate that urban expansion is amplifying volcanic risk and highlight the need to integrate hazard data into urban planning.
Meredith et al. (Thu,) studied this question.