Comparing surface- and canopy-layer urban heat islands over Beijing using MODIS data

The canopy-layer urban heat island (CLHI) and the surface-layer urban heat island (SLHI) of Beijing, the capital city of China, were compared on the spatial scale of a city and the temporal scale of a year in this study. A differential temperature vegetation index (DTVX) method was improved by suggesting a new parameterization scheme for estimating daytime air temperature (T-a); a binary linear regression equation was developed for estimating night-time T-a from Moderate Resolution Imaging Spectroradiometer (MODIS) land-surface temperature (T-s) and vegetation indices data during 2009-2010. Validations using weather station observations show that the spatially distributed T-a can be obtained with an accuracy of approximately 2 K. Comparisons between the CLHI and the SLHI indicate that the CLHI agrees well with the SLHI during night-time, but they have a greater difference during daytime either in heat island intensity or in spatial distribution pattern. The SLHI-CLHI intensity difference during daytime has a noticeable seasonal variation, which is small and negative in cold seasons, but large and positive in warm seasons, whereas that at night-time has no significant seasonal variations. The difference in the evapotranspiration cooling effects between urban and rural areas may be the predominant factor that drives the SLHI-CLHI difference.