Modeling the relationship between the urban development and subsurface warming in seven Asian megacities

The authors used a mesoscale climate model, CSU-MM and digital land-use data from seven Asian megacities to simulate ground surface temperature (Tsfc) related to urbanization for three discrete years of the 20th century. The variability of Tsfc was compared with the measured vertical profiles of subsurface temperature in the targeted megacities, which were expected to record the historical time-series of Tsfc. Considering a calm and clear day of the hottest season, results showed that Tsfc increased about 1.1 K 100 y−1 during the 20th century. Considering the seasonal climate variability, simulations were run for three additional cases (rainy day in the hottest season; clear day and rainy day in the coldest or rainy season) for each year in each megacity. The difference between the rates of change of Tsfc in Bangkok (0.9 K 100 y−1) and Tokyo (1.9 K 100 y−1) is considerable, which suggests that the differences of annual climatic variability are important for the analyses of urban subsurface warming. The authors conclude historical digital land-use data are useful to study past urban climate change in numerical simulation, and difference of annual climatic variability brings the difference of subsurface warming in each megacity.