Substantial Increase in Heat Wave Risks in China in a Future Warmer World

Abstract

Increases in the frequency and intensity of heat waves have serious impacts on human health, agriculture, energy and infrastructure. Here we use three simple metrics including the number of heat wave days, the length of heat wave season, and the annual hottest day temperature to characterize future changes in heat wave severity in China, based on large ensemble simulations conducted with the Canadian Earth System Model Version 2 (CanESM2) in the context of emergency preparedness. A heat wave day is defined as a day with daily maximum temperature reaching heat alert level (35°C). We find that global warming is associated with more severe heat waves including more heat wave days, longer heat wave season and higher hottest day temperature, and expansion of regions impacted by heat waves. While the increase in the magnitude of extremes in heat wave metrics with global warming level is close to linear, the increase in the frequency of extremes is much faster. For example, the historically hottest summer in 2013 in Eastern China, which occurs about one in 5 years in the 2013 climate, is projected to become more frequent than one in 2 years under 1.5°C global warming and almost every year would be worse than 2013 under 2°C warming. Additionally, the increase in the frequency of the extreme events is larger for rarer extremes. The frequencies for once-in-5-year, once-in-10-year, and once-in-50-year events increase by 2.5, 3.5, and 5.5 times under 1.5°C global warming, respectively.Plain Language Summary Heat waves have serious impacts on human health, agriculture, energy, and infrastructure. Though a few studies have investigated the future changes in heat waves in China, the heat waves defined in those studies are seldom of direct relevance to emergency preparedness. Here we study changes in heat wave days that are defined as daily maximum temperature above 35°C, a threshold for issuing a heat alert according to China's national Standards. We examine three simple metrics including the annual number of heat wave days, the length of heat wave season, and the annual hottest day temperature based on large ensemble simulations of CanESM2. We find that global warming is associated with more severe heat waves including more heat wave days, longer heat wave season, higher hottest day temperature, and expansion of regions impacted by heat waves. The increase in the heat wave metrics with global warming level is close to linear, while the increase in the frequency of extremes in these metrics is much faster. For example, the once-in-5-year event in the current climate, with a magnitude of the historically hottest summer in 2013 in Eastern China, is projected to become more frequent, to become a once-in-2-year event under 1.5°C global warming and every year event under 2°C global warming.

Compound Droughts and Heat Waves in China

“…It is difficult to compare different results of drought, because the differences in the period of analysis, data sources, the number of stations (or gridded data), and drought indices collectively contributed to inconsistencies in the results [50]. For heat waves, accelerated worsening of heat wave in China has been observed and acknowledged by many researchers [51][52][53]. Our results demonstrate again that the warming trend is unprecedented.…”

A Detectable Anthropogenic Shift Toward Intensified Summer Hot Drought Events Over Northeastern China

“…The above analyses suggest that anthropogenic activity may increase the occurrences of SHDEs over NEC. Besides, previous studies also indicated that there might be more extreme events (Sun et al, ) and more drought events across China in the future (Chen & Sun, ; Dai & Zhao, ; Li, Chen, Wang, & Yu, ), which have great impacts on the security of socioeconomic systems (Yu et al, ). The issue of how the severity and the occurrence probability of SHDEs over NEC change due to the continuous GHG emissions in the future is thus investigated under different emission scenarios of RCP4.5 and RCP8.5.…”

Contribution of Global Warming and Atmospheric Circulation to the Hottest Spring in Eastern China in 2018

“…Accordingly, changes in the probability of a 2018-like high-temperature event due to human and circulation influence can be evaluated without specific condi- tioning. For the definition of the current climate state for the year 2018 in CanESM2, the 10-year period of 1995−2004 in the model was considered to represent the current 2018 climate, as the global mean near-surface temperature (GMST) in model simulations increased by 1°C above the preindustrial level in this period (Sun et al, 2018a), the same as with the observed change of GMST in 2018. Therefore, the sample size in CanESM2 was 500 (50-member × 10-year), which is comparable to that (525) in HadGEM3A.…”

“…For example, eastern China suffered an extreme heat wave event in the summer of 2013 that caused economic losses of 59 billion RMB and lots of casualties (Hou et al, 2014). Under the medium RCP4.5 emissions scenario, heat waves in China are projected to become a common event in the coming decades (Sun et al, 2014(Sun et al, , 2018a. In the face of increasing risks related to climate change, world societies need to better understand these risks to prevent climate-related disasters, especially in areas with high levels of exposure and vulnerability.…”