Preplanned Studies: An Early Warning System for Heatwave-Induced Health Risks in China: A Sub-Seasonal to Seasonal Perspective — China, 2022

Global climate change has had a negative impact on the physical health of populations worldwide, with heatwave events causing significant human mortality and morbidity (1). The formation of an early warning system for health risks induced by heatwaves is vital, as it facilitates proactive measures by public health practitioners and public individuals. Current methodologies have developed various systems that provide advance warning several days ahead, effectively lessening heat-related dangers (2-6). The adoption of long-term pre-warning measures aids in preparing individuals and policymakers to take informed actions to reduce potential risks.

Despite the initial success of these long-term heatwave predictions, there remains a notable deficit in the provision of a health-risk warning system that covers the sub-seasonal to the seasonal scales (spanning two weeks to two months). The aim of this paper is to present a system that successfully addresses this gap.

By incorporating the China heatwave-attributable mortality model (7-8) with real-time temperature forecasts from the China Meteorological Administration-Climate Prediction System (CMA-CPSv3), this system provides up-to-date estimates of mortality rates and burdens for the forthcoming two months. As such, this system is poised to serve as a valuable tool for public health practitioners, enabling them to better plan personnel deployments and effectively allocate resources.

This study aims to combine heatwave events and health-risk assessment tools by using real-time, rolling temperature data projected for the subsequent 60 days from the advanced CMA-CPSv3 prediction system. Notably, the CMA-CPSv3 applies the enhanced resolution version of the Beijing Climate Center Climate System Model (BCC-CSM2-HR), recognized for its accuracy in predicting high temperatures within China (9). Initially, we commenced by systematically rectifying the temperature components produced by the CMA-CPSv3. A series of at least 3 days during the summer months (May to September) when the daily peak temperature surpasses the 92.5th percentile of the reference period (1961–2020) is characterized as a heatwave.

We utilized the nationwide heatwave-attributable mortality model established by Chen et al. (7-8) to analyze the health risks associated with heatwaves, including related mortality burden and death rate. This model investigates the specific exposure-response functional relationships between heatwaves and ensuing deaths across different climate zones using generalized linear models and meta-analysis. Estimations of mortality burden ascribed to heatwaves employ risk appraisals applicable to respective gridded heatwave series and nationwide mortality. The model considers factors such as population size, mortality rate, heatwave frequency, and exposure-response dynamics. By integrating the computed heatwave day data into the model, we ascertained the death burden and death rate due to heatwave-induced fatalities (depicted as gridded mortality burden per million population). A representation of this approach is illustrated in Figure 1.

Figure 1. 

Flow diagram illustrating the operational process of the early warning system.

Abbreviation: RCMs=regional climate models; RCP=representative concentration pathways; SSP=shared socio-economic pathway; CMIP=coupled model intercomparison project; RR=relative risk; AF=attributable fraction; DMT=daily maximum temperature.

Table 1, issued on July 1, 2022, provides estimates for the number of heatwave days expected in China over the subsequent two months. Data indicate a higher projection of heatwave days for July in regions like Western Sichuan, Chongqing, and other areas of Central China, with more than 20 heatwave days predicted per month. Similarly, nearly 20 days of heatwave occurrences were estimated for Northwest China, inclusive of areas such as Ningxia and Xinjiang. Moving into August, the northern reaches of Northeast China forecast an increased frequency of heatwave days, with most regions predicted to experience over 20 such days per month on average. Of particular note is the Yangtze River Basin, which endured the most intense heatwave event ever recorded in the late summer of 2022 (10). As outlined in Table 1, this model accurately predicted this distinct pattern a month in advance.

The projected results were released on July 1, supplemented by real-time daily forecasts for one-month duration heatwave days in the summer of 2022. Figure 2 compares estimated and actual data, with solid lines reflecting observed data and dashed lines illustrating CMA-CPSv3 predictions. The figure demonstrates CMA-CPSv3’s effective prediction of heatwave events during the summer of 2022. Accurate forecasting of heatwave days forms the basis for dependable subsequent estimations of heatwave health risks.

Figure 2. 

Comparison of the average heatwave days predicted over the next 30 days in China (dashed curve) with actual observations (solid curve).

The study provided an analysis of the mortality rate due to heatwaves in July and August 2022, as depicted in Table 1. When contrasted with heatwave occurrences, the distribution of heatwave-related mortality correlates strongly with heatwave patterns in central China. Henan and Sichuan, both populous provinces, recorded the highest mortality rates due to heatwaves, with approximately 3,400 and 2,000 deaths respectively. Upon conducting a subgroup analysis, cardiovascular diseases (CVD) emerged as the leading cause of heatwave-induced mortality, contributing to an estimated 80% of the cases. Further, seniors and females were found to be at a relatively higher risk, accounting for around 75% and 70% of cases respectively.

The mortality burden indicator can enable policymakers and public health practitioners to allocate resources effectively. Nonetheless, it is crucial to acknowledge that the impact of the mortality burden during heatwaves is related to the local population size, which may limit its relevance on an individual basis. Therefore, this indicator also includes a heatwave-related mortality rate, derived from the mortality burden per million people during heatwaves. Over a span of two months, the highest risk was observed in Xinjiang, with an estimated heatwave-related mortality risk of about 20,000 per million individuals monthly. This was closely followed by Inner Mongolia, which had a risk estimated at 10,000 individuals per million monthly. Notably, the risk in August surpassed that of July.