Living on the Edge: Unequal Rise of Global Population Exposure on Steep Terrain

Chakshu Gururani , Ugur Öztürk, Thorsten Wagener 

The global population living on steep terrain is rising, so is their landslide risk. However, hotspots and driving mechanisms of increasing exposure remain poorly understood. We assess changes in global gridded population and settlement characteristics on steep terrain (≥ 10◦ hillslope inclination) aggregated over topographic catchments (mean area ∼10,000 km2) for 1975–2025. We find that about 341 million additional people now live on steep terrain, increasing the total from 494 to 835 million. The strongest growth occurred in tropical catchments, commonly in peri-urban areas, indicating that exposure is increasingly forming in rapidly expanding settlement fringes. More than half of this growth occurred in low- and lower-middle-income countries. Hence, further exacerbating those countries’ global socio-economic disadvantage, exposure is rising in places with strained planning and response capacity. Our results provide a global baseline identifying priority regions for hazard monitoring and risk-informed planning.