Constraining the uncertainty of urbanization effect on surface air temperature change over the Beijing-Tianjin-Hebei region in China

Quantitative assessment of urbanization effect on surface air temperature (SAT) change provides crucial basis for formal detection and attribution analyses of climate change. However, debates about urbanization-related warming bias in documented regional SAT trend still persist, mainly due to different determination of rural stations. Here the urbanization effect on SAT change over the Beijing-Tianjin-Hebei region in China during 1980-2019 is estimated through three kinds of ways (i.e., comparisons between urban and rural stations [arithmetically station-averaged], urban-dominated and rural-dominated patches [patch-weighted mean], and realistic urban and rural areas [area weighted mean]). The last method explicitly takes urban and rural land cover fractions into account when calculating urban/rural and regional mean SAT trends. Urbanization-induced warming in the annual mean SAT change of urban stations (areas) through the three ways are estimated as 0.159 degrees C, 0.195 degrees C, and 0.138 degrees C per decade, respectively. And urbanization effect on regional averaged annual mean SAT calculated by patch-weighted and area-weighted methods are 0.113 degrees C and 0.050 degrees C per decade, respectively, which account for 33.8% and 14.8% of the total regional warming. The urbanization effect on observed SAT change estimated by considering realistic urban/rural land cover proportions is much lower than traditional station-unweighted way.