Changes In Extreme Heat And Precipitation Events In The Beijing-Tianjin-Hebei Region And Prediction Of Future Climate Scenarios

Extreme climate events have increased significantly in the context of climate change,with serious impacts on ecosystems and human socio-economics as well as daily life.Temperature and precipitation are important indicators of climate change.In this paper,we take BeijingTianjin-Hebei(BTH)region as the study area,analyze the spatial and temporal variation characteristics of extreme heat and extreme precipitation events in BTH region for the past 40 a from 1981 to 2020,and deeply explore the evolution characteristics and influencing factors of heat island effect in three major cities,Beijing,Tianjin and Shijiazhuang,under the extreme high temperature events.Finally,the latest CMIP6 model data are used to explore the average climate change trends in the BTH region under different scenarios in the future.It provides a theoretical basis and foundation for predicting the future climate change trends in the BTH region and coping with climate disasters.The main conclusions are as follows:(1)From 1981 to 2020,the intensity and frequency of extreme heat events in the BTH increased,and the interdecadal variation of extreme heat events was fluctuating.High temperature and sultry weather occur earlier and last longer in BTH region,and the synchronization increases.Spatially,extreme heat events occur mostly in the southern part of the BTH region.The increasing trend of high temperature days is most significant in Beijing,Tianjin,and Shijiazhuang,and the stations with large growth rates are concentrated in urban areas.In the context of climate change,the interdecadal ratio of the number of hot and sultry weather day to the number of hot and sultry weather days indicates that the probability of hot and sultry weather day in the BTH region increases significantly with interdecadal changes,and the high-value area is near the Bohai Sea region(Tianjin,Tangshan,and Cangzhou),i.e.,hot and sultry weather occurs more often along the Bohai Sea where the relative humidity of air is higher.(2)The UHI of Beijing,Tianjin,and Shijiazhuang all show an increasing trend in the last40 a.The UHI in Beijing is stronger.The seasonal change pattern of UHI in the three major cities is obvious,which shows that: winter > autumn > spring > summer.In terms of spatial distribution,the spatial distribution characteristics of UHI in Beijing are obvious,and the high value area extends to the southeast to Tongzhou district,a sub-center of the city,with UHI reaching 1.6 ℃;the heat island effect in Tianjin is weaker,and UHI has a tendency to expand to the southeast;UHI in Shijiazhuang spreads in a circular pattern from the high value center to the surrounding as the years go by,among which UHI in Xinle city has the largest increase at about 1.0℃.Population density and construction land are the most important factors affecting the urban heat island effect.(3)From 1981 to 2020,the intensity and frequency of extreme precipitation events in the BTH region weakened.The spatial distribution of extreme precipitation events is concentrated,and the spatial distribution of maximum rainfall days is characterized by "more in the east and less in the west,more in the north and less in the south",and the spatial distribution of the number of heavy rainfall days and extreme heavy rainfall days is less different,and the high value areas are mainly concentrated in the transition zone from the mountainous area to the plain area in northern Hebei: Beijing,Chengde,Tianjin,Tangshan and Qinhuangdao.In the2000 s and 2010 s,the precipitation concentration the BTH region is more concentrated,and the precipitation concentration period is gradually delayed from northeast to southwest.(4)The CMIP6 model simulates the average temperature and precipitation in the BTH region with some errors,and the simulation of temperature performs better than the simulation of precipitation.For air temperature,the average simulated value of the model ensemble is lower than the measured value;the average simulated precipitation of all model ensembles is higher than the measured value.From the simulation results,the average temperature and precipitation in the BTH region show an increasing trend under two different future scenarios(SSP2-4.5 and SSP5-8.5),and the higher the radiation scenario,the greater the rate of increase.The regions where the annual mean temperature increases significantly are mainly concentrated in the southern part of the BTH region,with an increase of about 1.5～2.0 ℃.The average annual precipitation is increasing in the whole BTH region,and the increasing area is mainly concentrated in the eastern part of the BTH region,with an increase of about 60～80 mm.In summary,this study discusses the temperature and precipitation characteristics of the BTH region in detail,and comprehensively analyzes the spatial and temporal characteristics of the intensity and frequency of extreme heat and precipitation events in the BTH region;meanwhile,using CMIP6 multi-model data,the future climate change trends in the BTH region under different scenarios are predicted and analyzed,providing a theoretical basis for predicting the future climate change trends in the BTH region and coping with climate disasters.