Assessment And Correction Of Urban Bias In Surface Air Temperature Series Of Eastern China Over Time Period1913-2012

Based on the monthly average maximum temperature and minimum temperaturedata from9stations which are located in the eastern China，we have made a qualitycontrol, and also a detection and adjustment of the discontinuities resulting fromrelocations using a statistical procedure in combination with the station’s historyinformation. The several rural stations around each of the urban stations are selectedby using the data of remote sensing to determine the relative locations of theobservational sites in the spatial distribution of surface brightness temperature.Applying surface air temperature data of AWSs in the rural areas and the target urbanstations for the last3years，the accumulated urbanization effect and its contributionare calculated. With an assumption that accumulated urbanization effect increase at aconstant rate，a linear correction method is used to correct the urban bias for thesurface air temperature series of the urban stations over1913-2012.(1) Analysis of the homogenized data indicates that the warming trend in annualmean temperature and the decrease trend in annual mean diurnal temperature range(DTR) get larger than those of the original data.(2) The accumulated urbanization effects for annual mean maximum，minimum，average temperature and DTR of the homogenized series for eastern China are0.082℃、1.858℃、0.970℃and-1.776℃respectively，corresponding to the respectiveurbanization effects of0.008℃/10a、0.186℃/10a、0.097℃/10a and-0.178℃/10a，and the urbanization contributions of7.8%、61.1%、47.5%and89.0%.(3) The accumulated urbanization effects lead to increase in seasonal meanmaximum temperature except for Summer，and increase in seasonal mean minimumtemperature and average temperature. Urbanization cause a large decrease in theseasonal mean DTR.(4) We correct the urban bias for the time series of the9stations of eastern China.After that，the increasing rate of the annual minimum and average temperature arebrought down from0.304℃/10a and0.204℃/10a to0.119℃/10aand0.108℃/10a，and the decreasing rate of annual mean DTR gets from-0.200℃/10a to-0.022℃/10a.After having corrected the urban bias，the increasing rate of the seasonal minimum and average temperature are much weaker than the homogenized data，while the trends ofthe seasonal maximum almost remain unchanged.(5) Beijing Station is taken as an example. The analysis shows that theaccumulated urbanization effects for mean minimum，average temperature and DTR inthe homogenized data series are all large positive values，in spite of the small negativevalue for annual mean maximum. After having corrected the urban bias for the timeseries of the station，the increasing rate of the annual mean minimum and averagetemperature，and the decreasing rate of annual mean DTR，are all brought downsignificantly.