Evaluating the contributions of urban surface expansion to regional warming in Shanghai using different methods to calculate the daily mean temperature

Abstract

The contributions of urban surface expansion to regional warming over subregions of Shanghai and Shanghai as a whole using different methods to calculate the daily mean surface temperature (SAT), including the averages of four daily time-records (0000, 0600, 1200, and 1800 UTC; T4), eight daily time-records (0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100 UTC; T8), and the averages of the SAT maximum (Tmax) and minimum (Tmin), Txn, were compared based on simulated results using nested numerical intergrations with the Weather Research and Forecasting regional climate model, where only the satellite-retrieved urban surface distributions differed between two numerical experiments. The contributions from urban-related warming expressed similar intensities when using T8 and Txn, while the smallest values occurred when using T4 over different subregions of Shanghai (with the exception of areas that were defined as urban for both time periods (U2U)) and Shanghai as a whole. Similar values for the changing trends could be detected over different subregions when no urban surface expansion (EX1) was detected for both T4 and Txn. The corresponding values increased under urban surface expansion (EX2) and varied over different subregions, revealing much stronger intensities over urban-surface expansion areas; the weakest intensities occurred over U2U areas. The increasing trends for EX2 and relative contributions when using T4 were smaller than those when using Txn, with the exception of those over U2U areas, which could be explained by the changing trends in Tmax and Tmin due to urban surface expansion, especially during intense urban expansion periods.

Keywords

• Urban surface expansion
• urban-related warming
• surface air temperature
• maximum
• minimum