Author(s): Liqun Sun
Linked Author(s):
Keywords: Urbanization; China; Weather station data; MODIS; Global warming
Abstract: Climate change and global warming are noted as mixable terminology to indicate the anthropogenic influence on climate variation, and it seems that such anthropogenic influence may result in mostly irreversible negative impacts on our environment and society. To evaluate anthropogenic influence, a large number of studies have explored the urban heat island effects (or partly regarded as urbanization influence) on local climate through analyzing urban and associated rural weather observations. The evidence of global warming comes from land-based station temperature observations; therefore, intuitively, it is a question whether the urbanization has influenced our estimation of global warming. This is the motivation of the present study. Using the observed temperature data and land use data over Mainland China, this paper develops a new method to evaluate urbanization influence on temperature station data. The Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product (MCD12Q1) in 2011 is used to extract the urban area percentages (UAPs) within the circles centered at each weather station for the radii of 2 km, 4 km, 6 km, 8 km and 10 km, respectively. Then, according to the UAPs, this paper categorizes weather stations into urban and rural groups. Over Mainland China, totally, 772 weather stations are used and categorized into 7 groups. Among them, six groups are defined by using different UAPs of the circles with 2 km radius and 10 km radius, the seventh group is defined for the stations with their elevations higher than 2000 meters. According to the UAPs, the stations in G1, G2 and G3 are regarded as urban stations, and G4, G5, and G6 are rural stations. The urbanization effects are explored by analyzing annual maximum (Tmax) and minimum (Tmin) temperature time series of these groups for the time period from 1961 to 2011. The results reveal that there is no considerable increase from the 1960s to the 1970s for most of the stations over mainland China. Nevertheless, form 1984 to 2007, the trends of Tmin for the urban stations are larger than those of the rural stations; specifically, the trends of Tmin data increase about 0. 79 °C/decade for Group 2 and only 0. 57 °C/decade for the Group 6. Meanwhile, for the Tmax trends, there is no considerable difference among those station groups for the study period. This study indicates that the urbanization has resulted in over-estimation of the Tmin (and associated daily temperature) over Mainland China, and it can be inferred, in a certain extent, that the global warming might be slightly over-estimated due to the urbanization influence.
Year: 2013