A numerical and field investigation of underground temperatures under Urban Heat Island

This paper introduces a simplified model for underground temperature prediction in summer hot weather. The data of 14 observation sites show that the surface temperature curves are close to trapeziums, and surface temperatures are related to air temperatures. Therefore, approximated temperature trapeziums that are determined by high- and lowest air temperatures can be used to simulate the underground temperature variation. Two observation sites respectively in the urban and suburban areas were used as examples. Good agreement was obtained between simulated- and measured temperatures. Measured data indicate the average temperature under urban concrete surface is 3.70 °C greater than that of suburban bare surface. The deviation is due to the heat urban environment effect and different surfaces effect, which are about 1.68 °C and 2.02 °C, respectively. Combined with soil volumetric water content (wv), ‘Heat’ Islands associates with ‘Dry’ Islands, which means urban soil moisture is lower than suburban soil moisture (13.9%). According to the variation of wv and temperature deviation graphs, Urban Heat Island, ground surface types and rainfall are important factors that influence the underground soil moisture and temperatures.