Urban-rural differences in the local human exposure to humid heatwaves in the Northern Hemisphere

Human exposure to humid heatwaves develops with the significant intensification of extreme humid-heat and population agglomeration. Although urban areas are typical spaces the heat stress, urban heat is expanding outward to rural areas spatially. However, the differences of long-term changes and attributions between urban and rural human exposure to humid heatwaves is still unclear, especially lacking global comparisons supported by continuous series. We used a new global wet-bulb temperature dataset and integrated scenario data to assess historical and future human exposure to humid heatwaves in the Northern Hemisphere. The differences between urban and rural areas in the contribution of enhanced heatwaves and increasing population were quantified. About 96.62% of the stations had pronounced increases in human exposure among those with significant changes. The domination of enhanced heatwaves to human exposure rate is stronger in urban areas in typical developed countries, while domination of increasing population is higher in rural areas in eastern China, with 87.5% of rural stations dominated by population growth. Under extremely increasing conditions in SSP5 scenario, average rates of human exposure to humid heatwaves in rural areas was 11.78% higher than urban areas. Our findings provide a scientific cognition for the local risk of humid heatwaves.