Regional warming induced by urban surface expansion in Shanghai

Abstract

To detect the impacts of urban surface expansion on surface air temperature at 2-m (SAT) in Shanghai, China, nested numerical integrations based on satellite-derived urban data between the 1980s and 2010s were performed using the Weather Research and Forecasting (WRF) model. Urban surface expansion induced an annual-averaged warming of 0.31 °C from 1980 to 2016 across the whole of Shanghai, showing the greatest intensity between 2010 and 2016. The values were 0.36, 0.78, and 0.75 °C over grids that were classified as urban in both time periods (U2U), land-use grids that changed from non-urban to urban (N2U), and urban areas (including U2U and N2U), respectively, and revealed weak warming over the inner-ring areas because the urban surfaces had been there since the 1980s, whereas warming areas were coincident with the outward expansion of the urban surface. Meanwhile, marked seasonal variations could be detected, which were greater in spring and summer but less in autumn and winter. The approximately homogenously distributed SAT maximum (weaker) and heterogeneously SAT minimum (stronger) contributed to the decreased diurnal temperature range. Regional warming induced by urban surface expansion was approximately 0.12 °C per decade, which accounted for 19% of the overall warming across the whole of Shanghai. The values were 0.11 °C per decade and 0.39 °C per decade over U2U and N2U, which accounted for approximately 17% and 42% of the overall warming, respectively, and resulted in approximately 41% of the overall warming over urban areas.

Keywords

• Urban surface expansion
• surface air temperature
• regional warming
• nested integration
• warming trend