Interdecadal Variation of Summer Extreme Heat Events in the Beijing–Tianjin–Hebei Region

Abstract

Extreme heat events are frequent in the Beijing–Tianjin–Hebei (BTH) region due to global warming and accelerated urbanization. While previous studies have analyzed the trend of extreme heat events in the Beijing–Tianjin–Hebei (BTH) region, the interdecadal changes of these events remain unclear. Therefore, this study aims to analyze the interdecadal temporal and spatial characteristics of summer extreme heat events in the BTH region using daily mean and maximum temperature datasets from 174 stations over the period 1979–2020. The results are shown as follows: (1) From 1979 to 2020, extreme heat events showed an overall upward trend in the BTH region. There were similarities in the changes in the extreme maximum temperature (TXx) and the number of high-temperature days (Htd) between different generations, and both were low until the mid-1990s. (2) In terms of the spatial pattern, TXx and Htd both showed the spatial distribution characteristics of being high in the south and low in the north. Extreme heat events in the BTH region were mainly concentrated in Beijing City, Tianjin City, and the eastern region of Hebei, and the TXx increase in most areas reached 1.5–2.0 °C. (3) The number of high-temperature days (Htd) increased significantly in the background of global warming, especially in Beijing, Tianjin, and Shijiazhuang Cities. (4) Extreme heat events in the BTH region mainly occurred in June and July, and the interdecadal changes showed a decreasing trend in June and an increasing trend in July. A high proportion of Htd was concentrated in Northern Hebei Province in July.

Quantitative Analysis of Spatiotemporal Patterns and Factor Contributions of Surface Ozone in the North China Plain

“…It was observed that from 2019 to 2021, the majority of months with the highest frequency of ozone pollution in the region were concentrated in June. Therefore, the month of June was predominantly identified as the period with the greatest number of ozone content exceedances in the NCP, primarily associated with the prevalence of high temperatures, intense ultraviolet radiation, and scant rainfall in most areas of Beijing, Tianjin, and Hebei during this month [46][47][48]61,62]. Additionally, the peak levels of ozone pollution along the coastal regions of Hebei, Tianjin, and Shandong in 2019 and 2021 were noted to occur in May.…”

“…Among these four seasons for the averaged MDA8, as shown in Figure 4a-d, O 3 pollution was highest in summer, followed by spring, then autumn, and the O 3 pollution was the lowest in winter. This is mainly due to the fact that during summer, the ultraviolet radiation is the strongest and the temperature is the highest, which is suitable for the photochemical reaction for the generation of ozone [46][47][48]. From the perspective of the spatial pattern of O 3 pollution, the most serious O 3 pollution area is in the border area of Hebei, Shandong, and Henan Provinces, that is, the southern part of Hebei, the northern part of Henan, and the western part of Shandong.…”

“…From the perspective of the spatial pattern of O 3 pollution, the most serious O 3 pollution area is in the border area of Hebei, Shandong, and Henan Provinces, that is, the southern part of Hebei, the northern part of Henan, and the western part of Shandong. This is due to the dense population of these areas [15,49,50], the high level of human activities [51,52], and the resulting high anthropogenic emissions, while the strong ultraviolet radiation and high temperature in summer [46][47][48] greatly enhances the photochemical reaction level of O 3 , and the ozone pollution level is also the most serious. Furthermore, it was observed that the concentrations of O 3 pollution were comparatively reduced during the spring season when analyzed against those prevalent in the summer period.…”

“…This decline may be correlated with the COVID-19 pandemic [53,54] and is also attributed to the government's ongoing implementation of collaborative emission reduction policies for PM 2.5 and O 3 pollution [30,[64][65][66]. Among all months, June exhibited a trend of initial increase followed by a decrease in ozone pollution from 2019 to 2021, potentially due to the elevated temperatures in June 2021, which contributed to an upsurge in the net photochemical production of ozone [47,48,61,62]. The main reasons for the ozone peak in June are high temperature and strong solar radiation.…”