Increasing population exposed to both seismicity and flooding in low-income countries

Natural hazards pose a significant challenge to the sustainable development worldwide. To gain a comprehensive understanding of their risk, it is crucial to investigate the population exposure to multiple hazards. Nevertheless, previous studies have mainly focused on single hazard exposure, leaving a notable gap in the interplay of multiple hazards in relation to population dynamics. This paper takes seismic and flooding as examples, and analyses the global population exposure to the two individual hazards and their intersection. Results showed that 2.48 billion inhabitants (32.26% of the global population) were exposed to the natural hazards of seismicity or flooding in 2020. Notably, 152 million people lived in the intersected seismic-flood hazard zones (ISFH), with a population density reaching 4.71 times of the global average. During 2000–2020, the ISFH population increased by 31.55%, surpassing the global average of 28.08%. Remarkably, the vast majority (80.54%) of the ISFH population growth occurred in low and lower-middle income countries. Analysis of future scenarios indicate that the residents located in the ISFH zones in low-income countries would keep increasing until at least 2100, regardless of scenarios considered. These findings shed light on understanding and managing multi-hazard risk, particularly in low and lower-middle income countries.