TROPICAL GEOGRAPHY ›› 2018, Vol. 38 ›› Issue (2): 236-243.

### Research on the Recognization of the Impact of Climate Change and Urbanization on Surface Warming Using Subsurface Heat Tracer

DONG Linyao，YU Zhiqiang，XU Jinxin

1. （Changjiang River Scientific Research Institute，Changjiang Water Resources Commission，Wuhan 430010，China）
• Online:2018-03-05 Published:2018-03-05

Abstract: Greenhouse gas emissions and urbanization both contributes to the surface warming events, but in two different modes, and it has been difficult to separate these two influences. Subsurface heat is an effective implement to detect and separate these two effects. Subsurface temperature-depth profiles in 28 observation wells in urban and rural areas in Kumamoto plain, Japan, was observed to inversely detect the surface warming rate based on the analytical solution of one dimensional unsteady water-heat flow transport equation, and the air temperature in 7 meteorological stations was also analyzed for comparative purpose. The results show the following: (1)The estimated surface warming values range from 0.34 °C (well No. 23) to 1.91 °C (well No. 13). The high surface temperature increase commonly occurs in the urban areas, whereas the low surface temperature increase mainly occurs in the rural areas. Only well No. 18 shows a relatively low surface temperature increase (0.78 °C). It is located in the central part of Kumamoto city with an urban land use since 1965. (2)The average GST increase obtained from temperature-depth profiles in the expanded urban area is about 1.51°C, while the average increase estimated in the rural wells is about 0.81°C. It is highly probable that the urbanization effect contributes the same amount as climate change to surface warming in the study area, and the subsurface heat can serve as an effective tracer to detect this phenomenon; (3)The surface warming rates in SAT of M1–M3 range from 0.04 to 0.054 °C per year, while the rates in SAT of M4-M7 are about 0.025°C per year. The impacts of urbanization and climate change on SAT visible in the data. The meteorological stations M1-M3 lie in the expanded urban areas, and the surface warming rates were associated with both the urbanization and climate change issues. Stations M4-M7 are located in the rural areas, and the surface warming rates were caused only by the climate change. The surface warming rates obtained from the fitted SAT series indicate that the urbanization contributes the same amount to the rising of SAT as climate change. The contribution of urbanization to surface warming was confirmed by the SAT records from 1978 to 2012. The average SAT increase in expanded urban area from 1987 to 2012 is 1.13 °C, while the average increase in the rural area is 0.59 °C. The urbanization effect thus contributes the same amount as climate change to the increase of SAT. A direct link was found between ground surface and air temperatures. The urbanization effects contribute the same amount as climate change to the increase of both GST and SAT. However, the variations of estimated GST are higher than the observed SAT, which might be associated with the different mechanisms involved in the variations driven processes of GST and SAT. The temperature-depth profile serves as an effective tracer to separate urbanization from climate change effects on the surface warming. However, the uncertainty involved during the calculation process limits the employment of the heat tracer implement, and the approach needs to be investigated deeply.