Projected burden of humid-heat on paediatric asthma in Shanghai under climate change scenarios: A time-series study

Climate change is intensifying the frequency and severity of extreme heat events. While the impact of temperature on respiratory health is well-documented, the synergistic effects of combined heat and humidity are less clear, especially for children, a population with heightened vulnerability. This study investigates the differential impacts of humid heat (measured by Wet-Bulb Globe Temperature, WBGT) and temperature alone on paediatric asthma emergency department visits (EDVs) in Shanghai, China, and projects the future disease burden under climate change. We conducted a time-series analysis of 42,604 paediatric asthma EDVs recorded across 66 hospitals in Shanghai during the summer seasons of 2016–2018. Distributed lag non-linear models were used to quantify the association between daily EDVs and both WBGT and temperature. We projected future humid-heat-related asthma burden through 2099 under four Shared Socioeconomic Pathway scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). Daily mean WBGT demonstrated a stronger association with paediatric asthma EDVs than temperature alone. Exposure to high humid-heat (WBGT at the 95th percentile) was associated with a significant cumulative relative risk (RR) of 1.38 (95% CI: 1.10–1.74) compared to the minimum morbidity WBGT over a 7-day lag. In contrast, the risk associated with high temperature alone was not statistically significant (RR = 1.15, 95% CI: 0.93–1.43). The risk of asthma exacerbations with WBGT was higher among males (RR = 1.48; 95% CI: 1.14–1.91) and children under 6 years (RR = 1.54; 95% CI: 1.06–2.21), and these effects persisted after adjusting for air pollutants. Projections indicate a substantial rise in the humid-heat-related asthma burden, with attributable cases potentially increasing 2.4-fold higher under SSP5-8.5 than under SSP1-2.6 by 2090–2099. Humid-heat exposure is more strongly associated with paediatric asthma exacerbations than high temperature alone in Shanghai. Our findings highlight vulnerable subgroups and project a substantial increase in future disease burden, underscoring the urgent need for targeted public health interventions.