Differences between Various North China Climatic Normals in Winter and Summer: A Study of Its Impact on Climate Monitoring

This research compared and analyzed the precipitation and temperature differences in North China during winter and summer under different climate conditions to explore the characteristics and differences between various climate normals in this region and their impacts on regional climate monitoring. Then, we analyzed the impact of these average climatic changes on extreme historical events. Investigations revealed that although the average precipitation in winter and summer during 1991–2020 (climate state Ⅱ) was more than that during 1981–2010 (climate state I), it was lesser than that in 1961–2020. However, the annual variation of state Ⅱ was smaller than that of state Ⅰ in winter, whereas vice versa in summer. Furthermore, although the state Ⅱ climate precipitation of the different regions varied in winter, it decreased in the central area and increased in the eastern and western parts of North China in summer. Also, we observed that the average winter and summer extreme precipitation thresholds in North China were higher in state Ⅱ (0.86 and 22.0 mm) than in state Ⅰ (0.83 and 21.6 mm), causing several extreme precipitation days in winter and summer in most parts of North China for the past 60 years. This event, however, reduced corresponding to state Ⅱ than Ⅰ. Although the average winter and summer temperatures of state Ⅱ were significantly higher than those of state Ⅰ, they remained higher than the average winter and summer temperatures of 1961–2020, indicating that while state Ⅱ temperatures maintained the characteristic of being overall warmer than state Ⅰ, the change characteristics of the different regions varied. Conversely, the extremely low average winter temperature and the extremely high summer temperature threshold in state Ⅱ (−9.8°C and 27.9°C) exceeded those in state Ⅰ (−10.2°C and 27.5°C), causing several extremely low winter temperature days in most parts of North China corresponding to state Ⅱ for the past 60 years. While this event increased compared with state Ⅰ, the extremely high summer temperature days corresponding to state Ⅱ reduced to varying degrees compared with state Ⅰ. Overall, our investigations propose that applying new climate normals will increase the extreme precipitation and extreme temperature thresholds in most parts of North China, leading to more frequent low temperatures, less precipitation, and less extreme historical climate events in climate monitoring. Hence, the possible impact of the new climate normals on climate monitoring and prediction over the next decade should be fully considered.