Projection of the cluster high temperature events in China and population exposure under 1.5℃ and 2℃ global warming

doi:10.12006/j.issn.1673-1719.2023.210

Abstract

Abstract:

Based on four dynamical downscaling simulations by the regional climate model RegCM4 (i.e., CdR, EdR, HdR, and MdR) and population projection dataset under SSP2-RCP4.5, the characteristics of the cluster high temperature events (CHTE) in China under 1.5℃ and 2℃ global warming were projected. The multi-model ensemble (MME) mean projection indicates the annual frequency increases by 31% and 44% respectively at the 1.5℃ and 2℃ warmer worlds compared with the reference period, and the extreme CHTE increases by 4.2 and 6.8 times respectively. Besides, the proportion of the CHTE indicators such as the cumulative intensity, duration, frequency falling into ‘large value range’ is expected to increase substantially. Compared with the CHTE under the 2℃ warming, a significant decrease of CHTE metrics across the country is projected at the 1.5℃ target, with remarkable regional differences. The reduction in frequency increases gradually from north to south. The duration decreases significantly by more than 6 days in Xinjiang and south of the Yangtze River (national averaged value is 0.2 days). The cumulative intensity decreases by more than 20℃ in the east-central China, and by more than 50℃ in the eastern part of Xinjiang (national averaged value is 0.6℃). In addition, under global warming of 1.5℃ and 2℃, MME projects that a widespread increase can be clearly found in the population affected by the CHTEs, with a significant decrease in the Inner Mongolia region and an increase in the central and eastern regions. The national population affected by the CHTEs increases by 1.4 times and 1.8 times, respectively. The urban population affected by the CHTEs increases more significantly (by 2.9 times and 3.8 times respectively), particularly with the most significant increase in the Beijing-Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta, and Central China. The intensity exposure shows a significant increasing trend (by 2.2 and 5.2 times respectively) under the 1.5℃and 2℃ global warming, the same as the comprehensive exposure (by 1.2 and 1.8 times respectively). By contrast, the CHTE intensity exposure and comprehensive exposure on the urban population increase by up to 10 and 4 times respectively under the 2℃ global warming.

Key words: Cluster high temperature event (CHTE), Global warming target, Regional climate model, Population exposure, Ensemble projection

CHENG Yang, HAN Zhen-Yu. Projection of the cluster high temperature events in China and population exposure under 1.5℃ and 2℃ global warming[J]. Climate Change Research, 2024, 20(3): 278-290.

Figures/Tables 10

Table 1 The crossing time in response to global warming of 1.5℃ and 2℃ in the future relative to pre-industrial level simulated by the four climate models under the RCP4.5

Table 2 The annual mean frequency of the simulated cluster high temperature events (CHTE) averaged over China under RCP4.5 scenario

Fig. 1 Relative frequency of the cluster high temperature events (CHTE) for each month averaged over China

Fig. 2 MME projected changes (relative to 1986-2005) of annual mean frequency (a, b), duration (c, d), and cumulative intensity (e, f) of the CHTE during the crossing times of global warming of 1.5℃ and 2℃

Fig. 3 MME projected changes of annual mean frequency (a), duration (b), and cumulative intensity (c) of the CHTEs in 1.5℃ compared with 2℃ warmer future

Fig. 4 MME projected changes of relative frequency distributions of each CHTE metrics in response to global warming of 1.5℃ and 2℃ (relative to 1986-2005)

Table 3 MME simulated mean value for each CHTE metrics

Fig. 5 The relative changes in total population (a), the population affected by the CHTEs (b), CHTE cumulative intensity population exposure (c), and CHTE comprehensive intensity population exposure (d) averaged over China and urban areas relative to 1986-2005

Table 4 The changes of population exposure to the CHTEs over China relative to 1986-2005

Fig. 6 MME projected changes of annual mean population affected by the CHTEs relative to reference period at the times of global warming of 1.5℃ and 2.0℃. (Data shown are the changes in affected population at each 0.25° ×0.25° grid point)

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