Background Evidence of the impacts of ambient temperatures on emergency ambulance calls (EACs) in developing countries is rare. This study aimed to examine the impacts and burden of heat on EACs in China, quantify the contributions of regional modifiers and identify the vulnerable populations.

Methods A semi-parametric generalized additive model with a Poisson distribution was used to analyze the city-specific impacts of the daily maximum temperature (Tmax) on EACs during June to August in 2014-2017. Stratified analyses by sex and age were performed to identify vulnerable sub-populations. Meta-analysis was undertaken to illustrate the pooled associations. Further subgroup analysis stratified by climate, latitude and per capita disposable income (PCDI) and meta-regression analysis were conducted to explore the regional heterogeneity and quantify the contributions of possible modifiers. City- and region-specific attributable fractions (AF) of EACs attributable to heat were calculated.

Results Strong associations between daily Tmax and total EACs were observed in all cities. 11.7% (95% CI: 11.2%–12.3%) of EACs were attributed to high temperature in the ten Chinese cities, and the central region with lower PCDI had the highest AF of 17.8% (95% CI: 17.2%–18.4%). People living in the central region with lower PCDI, the people aged 18-44 years and 0-6years were identified to be more vulnerable to heat than others. The combined effects of PCDI, temperature and latitude contributed 88.56% to the regional heterogeneity.

Conclusions Our results complement the understanding of the burden of EACs attributable to heat in developing countries and the quantitative contribution of regional modifiers.