Effects of site change and urbanisation in the Beijing temperature series 1977-2006

During 1977-1981 the Beijing (BJ) meteorological station was at a suburban location. In 1981 it was moved to a more urban location, but in 1997 it was subsequently moved back to the same suburban location. The daily BJ temperature series, together with those from 18 nearby stations, form a unique database for studying how site-change and possible urbanisation influences affect climate changes at a local scale. The site-change-induced biases were quantified, between 0.43 and 0.95°C, based on comparisons between multi-year-mean seasonal temperature anomalies at BJ and the mean of those from a cluster of nearby stations. The annual mean urban-suburban difference was 0.81°C around 1981 and 0.69°C around 1997, indicating a growing urbanisation effect in the suburban compared to the downtown area. The linear warming trend in the adjusted (for site moves only) BJ temperature series during 1977-2006 was 0.78°C/decade. Comparing with several rural and less-urban sites, we suggest that the BJ records include an urbanisation-related warming bias between 0.20 and 0.54°C/decade, likely about 0.30°C/decade, for the recent few decades. The climatic warming at BJ between 1977 and 2006 is likely, therefore, to be about 0.48°C/decade. Caveats for using these estimates were discussed.