Effect of Urbanization on Land-Surface Temperature at an Urban Climate Station in North China

While the land-surface temperature (LST) observed at meteorological stations has significantly increased over the previous few decades, it is still unclear to what extent urbanization has affected these positive trends. Based on the LST data recorded at an urban station in Shijiazhuang in North China, and two rural meteorological stations, the effect of urbanization at the Shijiazhuang station for the period 1965-2012 is examined. We find, (1) a statistically-significant linear trend in annual mean urban-rural LST difference of 0.27 degrees C (10 year)(-1), with an urbanization contribution of 100% indicating that the increase in the annual mean LST at the urban station is entirely caused by urbanization. The urbanization effects in spring, summer and autumn on the trends of mean LST are also significant; (2) the urbanization effect is small for time series of the annual mean minimum LST, and statistically marginal for the trend in annual mean maximum LST [0.19 degrees C(10 year)(-1)]; (3) the urbanization effect on the annual mean diurnal LST range (Delta LST) at the urban station is a strongly significant trend of 0.23 degrees C (10 year)(-1), with an urbanization contribution of 21%. The urbanization effects on trends in the spring and autumn mean Delta LST are also larger and more significant than for the other seasons; (4) the urbanization effects on the long-term LST trends are remarkably different from those on the near-surface air temperature at the same urban station. Nonetheless, the significant warming of the urban boundary layer is expected to affect the urban environment and ecosystems. However, the problem of data representativeness at an urban station for themonitoring and investigation of large-scale climate change remains.