Study of urban heat island index methods for urban agglomerations (hilly terrain) in Chongqing

To study the urban heat island (UHI) effect in the mountainous areas of Chongqing, the UHI indexes for the Chongqing urban agglomerations were investigated in the present study. This study is based on data from 34 national weather stations and more than 2000 regional automated weather stations in Chongqing, Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, and 30-m high-resolution land use data and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature remote sensing data for Chongqing in 2015. Moreover, the influences of three background temperature calculation methods on the UHI effect were compared. The results showed that, if only the land use data and the city clustering algorithm (CCA) were used to divide the urban and suburban areas, the strong UHI index of Chongqing exhibited an abnormal increase in the years with extremely high temperatures, and the corresponding divided suburban and urban areas had relatively large differences in altitudes, thereby overestimating the UHI index. Therefore, in the present study, a new method for dividing the urban and suburban areas based on the combined CCA and light intensity data and a division method with the altitudes calibrated on this basis were designed. Both methods were able to satisfactorily reduce the influence of extreme climate years and excessively large differences in altitudes on the UHI index calculations and provide a new approach for future studies of the UHI index for mountainous areas with large altitude differences.