A city-wide investigation on the subsurface temperature evolution and geothermal capacity evaluation

The subsurface urban heat island (UHI) effect can provide latent clean geothermal potentials for cities. Understanding the city-wide subsurface temperature evolution under different land surfaces is significant in making better use of geothermal energy. This research presents a study of Nanjing to identify the city-wide temperature distribution and evolution characteristics and further estimates the geothermal potential in Nanjing. Low-cost satellite-measured temperatures were used to derive the subsurface temperatures through a liner regression correction method, with higher accuracy verified by measured borehole data. The simulation results indicate that the concrete surface exhibits higher average temperatures than the grassland surface, resulting in relatively higher subsurface temperatures. The deviations of simulated subsurface temperatures are attributed to many factors, including the influence of complex atmospheric conditions on satellite-measured temperature accuracy, land surface heat absorption, and infiltration in the shallower layer. Furthermore, it reveals that the urban areas have 14.7% greater geothermal potential compared to rural areas, due to the subsurface UHI effect. This study provides a potentially efficient and convenient method for the estimation of potential urban geothermal energy.