Study On The Spatial And Temporal Variation Of Extreme Temperature Events In Beijing-Tianjin-Hebei Region And The Impact Of Urbanization On Them

The accelerated global warming and the frequent occurrence of extreme climate events have seriously affected ecological,social,economic systems as well as people's life.Relevant research results show that the frequent occurrence of extreme climate events is not only affected by increased climate variation,but also by urbanization.As the most representative extreme climate event,extreme temperature event is the basis and focus of research on extreme climate events.In this paper,the Beijing-TianjinHebei(BHT)region was selected as the research area.Based on the daily temperature observation data of 174 meteorological stations from 1980 to 2014,20 extreme temperature indexes were defined.With the combined methods of trend analysis,spatial interpolation,contrast analysis and correlation analysis,this research examined the temporal and spatial variation of extreme temperature index and impacts of urbanization on extreme temperature events.In this paper,the following four main results are achieved:(1)Based on the analysis of the 20 indexes,it is found that from 1980 to 2014 the extreme cold events in the Beijing-Tianjin-Hebei region as a whole showed a decreasing trend while the extreme warm events showed an increasing trend.The days with a great daily temperature difference showed a significant decreasing trend while those with a very small daily temperature difference showed a significant increasing trend.And the fluctuation of the daily temperature range is decreasing.(2)High accuracy surface modeling method(HASM)was first applied to interpolate the extreme temperature indices,with which the spatial variation of extreme temperature index was analyzed.The research also found that most sites afflicted by extreme cold events showed a trend of decrease and that the extreme warm events increased more obviously,especially in highly urbanized sites such as Beijing,but it is not obvious in regions with lower urbanization level such as cities in the north of Chengde.(3)With the consideration of population,Gross Domestic Product(GDP),land use and nighttime remote sensing data,clustering methods were used to classify meteorological stations on a fine spatial scale.Through comparative analysis between different types of sites,it is found that the increasing trend of extreme warm events in urban and suburban sites was larger than those in rural sites,and the increasing trend of urban sites was greater than that in suburban sites.Meanwhile,the decreasing trend of extreme cold events in both urban and suburban sites was also greater than that in rural sites.However,the decreasing trend of suburban sites was the largest.(4)Considering the features of the sites,this paper defined a comprehensive reference value for urbanization and analyzed its relation with the trend of extreme temperature index,which shows a certain relevance that the higher the urbanization level of the site was,the more frequent extreme warm events happened.It is also found that the trend of index reduction for extreme cold events was also more obvious,and the overall level of urbanization is more relevant to the former than to the latter.