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Contribution of urban surface expansion to regional warming in Beijing.

Beijing, the capital of China, is located in one of three city clusters in eastern China that have high economic vitality. With the rapid economic development and population explosion, marked urban surface expansion occurred in Beijing between the 1980s and 2010s. The contribution of urban surface expansion to regional warming as detected from meteorological observational station data may vary with considerable uncertainty because of the spatial heterogeneity of such data--a situation that promotes a requirement for numerical model-based investigations. Satellite-based images from 1980 to 2016 that have fine resolution over the three city clusters and show the urban surface expansion in China from rapid economic development and anthropogenic activity were used to perform a 37-year nested dynamical downscaling using the Weather Research and Forecasting (WRF) Model to quantify this contribution to regional warming.

The 37-year area-averaged annual urban-related warming across the whole Beijing area was 0.25[degrees]C. The contribution of land-use changes to the globally averaged surface air temperature (SAT) trend is unlikely to be more than 10%. However, the contribution of urban surface expansion to regional warming was approximately 22% of the overall warming in Beijing. The diurnal temperature range (DTR) in Beijing in summer decreased by -0.27[degrees]C.

The contributions to land-use grids that changed from nonurban (in 1980) to urban (in 2016; N2U) were much stronger than those to grids that were classified as urban in both time periods (U2U), which were closer to the values of urban areas (including N2U and U2U) because of the intense increase in urban surface areas. Urban-related warming expressed marked annual variation and was greater in the warm seasons and lesser in the cold seasons. The greater increase in SAT minimum and the weaker SAT maximum accounted for the decreased DTR.

Because of the special geographic characteristics for the plains areas of Beijing in the southeastern region and surrounding mountain areas in the northwestern region, respectively accounting for approximately 62% and 38% of the total area, urban-related warming was mainly concentrated in the plains areas. The 37-year area-averaged annual urban-related warming in the plains areas of Beijing was 0.52[degrees]C. The contribution of urban surface expansion to regional warming was approximately 42% in the plains areas of Beijing. The DTR in summer there decreased by -0.71[degrees]C.

In addition to urban surface expansion, other aspects, such as building density and height, aerosol emissions, and anthropogenic heat release, are not covered in our study because of the difficulties in monitoring as well as large uncertainties. Therefore more studies are necessary.--Deming Zhao (Chinese Academy of Sciences), and J. Wu, "Contribution of urban surface expansion to regional warming in Beijing, China," in the June Journal of Applied Meteorology and Climatology.

Caption: Spatial distributions of annual averaged urban-related warming ([degrees]C) between 1980 and 2016 in Beijing. Shaded areas passed the 90% confidence-level t test.

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Publication:Bulletin of the American Meteorological Society
Geographic Code:9CHIN
Date:Jul 1, 2017
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