Evaluation of surface heat fluxes in Chiayi plain of Taiwan by remotely sensed data

Surface energy processes have an essential role in regional weather, climate and hydrosphere cycles, as well in regulating urban heat redistribution. The Chiayi urban area of Taiwan and its surrounding agricultural plains are an appropriate complex for studying land surface parameters and energy fluxes of different land cover/land use types in an urban heat island. In this study, three micro-meteorological stations were established over Chiayi Plain to collect in situ reference observations from 2006. In order to properly characterize the surface heat fluxes over a regional scale by point measurement, Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images and images acquired by a high resolution airborne campaign in conjunction with meteorological data were used to estimate the surface heat fluxes over a large area. The analytical results indicated that surface heat fluxes determined from both airborne and satellite images were feasible for estimating surface heat flux. The correlation coefficient of surface heat fluxes with in situ corresponding observations exceeded 0.80. On the other hand, satellite-observed surface skin temperature and land surface energy fluxes were the core factors analysed in different land cover types. The urban surface was rather dry as half of net radiation is converted to sensible heat flux for heating the surface, whereas over 90% net radiation is converted to latent heat flux at wet surfaces such as evergreen broadleaf or water. Surface heat flux was also proven to be an indicator of the magnitude of urban heat island effect and the findings of this study encouraged further use of remotely sensed imagery for assessing the urban heat island effect.