Analysis Of Precipitation Variation And Identification Of Influencing Factors In Strong Human Activity Areas

Due to the dual effects of global climate change and human activities,the precipitation characteristics of many strong human activity areas have changed significantly,and the precipitation characteristics of urban and suburban areas are also different.The change of precipitation characteristics resulted in frequent extreme meteorological and hydrological events in these areas.The regional waterlogging and drought events also present an incrasing trend significantly.In order to deal with extreme meteorological and hydrological events in strong human activity areas,we should first clarify the precipitation variation rules and influencing factors,and figure out "what changes have taken place in the spatial and temporal characteristics of regional precipitation?-What are the differences in suburban precipitation changes?-What are the influencing factors of suburban precipitation difference?How much impact does the key factor have on precipitation?".The main problems in these four aspects need to make clear.In this study,Beijing-Tianjin-Hebei region,which is most disturbed by human activities,is taken as the research area.The evolution mechanism of regional precipitation is analyzed and a spatial-temporal evolution analysis method of precipitation is constructed.Firstly,the spatial-temporal distribution characteristics of precipitation in Beijing-Tianjin-Hebei region are compared and analyzed,which is further refined into two typical cities of Beijing and Tianjin,and the similarities and differences of urban-suburban precipitation change are analyzed.Based on the principal component analysis method,the identification method of dominant factors of urban-suburban precipitation variation difference is constructed,and the dominant factors affecting the precipitation difference between central and southern suburbs of Beijing are identified.The simulation accuracy of the model for regional precipitation is evaluated.The effect of urban anthropogenic heat on the typical heavy rain process in Beijing urban central area is verified.The main conclusions are as follows:(1)The precipitation in Beijing-Tianjin-Hebei region from 1961 to 2017 shows significant spatial and temporal variabilityIn Beijing-Tianjin-Hebei area,the precipitation index and intensity index of different temporal scales decreased mainly from 1961 to 2017,but most of them showed an upward trend in 1997-2017 series.The two indexes of wet-day precipitation intensity and annual precipitation total amount passed the significant test.Spatially,the index value of Beijing-Tianjin-Lang region is higher than that of other regions,and the index value of northern suburbs is lower than that of other regions.The interannual variation of light rain and moderate rain in Beijing-Tianjin-Hebei region increased significantly from 1961 to 2017,while the trend of heavy rain decreased significantly.In terms of precipitation structure,the proportion of heavy rain is the largest and the proportion of heavy rain is the smallest.The precipitation above heavy rain level in Beijing-Tianjin-Lang area is higher than that in other areas,and the precipitation below medium rain level in northern suburbs is higher than that in other areas.(2)The anthropogenic heat is the dominant factor affecting the precipitation of urban-suburban areas.Influenced by the large-scale regional climate conditions,the annual average precipitation total amount index and intensity index of Beijing from 2000 to 2012 are lower than that from 1978 to 1999.The decline extent of urban central area is smaller than that of suburbs.The annual average precipitation difference between the central area and the southern suburbs of Beijing changed from-13.4 mm in 1978-1999 to 10.7 mm in 2000-2012.Urban anthropogenic heat is the dominant factor causing the difference of precipitation between the central urban area and the southern suburbs of Beijing.(3)A numerical simulation scheme of precipitation considering modified anthropogenic heat improved the simulation accuracy of "7.21 rainstorm" in Beijing central urban area.The model reflects the effect of anthropogenic heat on precipitation in Beijing central area.The simulation effect of considering anthrpogenic heat scheme is better than that of the scheme without UCM.The precipitation values in the urban centre and surrounding areas have increased significantly,and the accuracy of precipitation simulation has been improved significantly.The model simulation results verify the enhanced effect of Urban Anthropogenic Heat on the precipitation in the urban centre.