Abstract
The urban heat island is generally conducted based on ground observations of air temperature and remotely sensing of land surface temperature (LST). Satellite remotely sensed LST has the advantages of global coverage and consistent periodicity, which overcomes the weakness of ground observations related to sparse distributions and costs. For human related studies and urban climatology, canopy layer urban heat island (CUHI) based on air temperatures is extremely important. This study has employed remote sensing methodology to produce monthly CUHI climatology maps during the period 2000–2013, revealing the spatiotemporal characteristics of daytime and nighttime CUHI during this period of rapid urbanization in Shanghai. Using stepwise linear regression, daytime and nighttime air temperatures at the four overpass times of Terra/Aqua were estimated based on time series of Terra/Aqua-MODIS LST and other auxiliary variables including enhanced vegetation index, normalized difference water index, solar zenith angle and distance to coast. The validation results indicate that the models produced an accuracy of 1.6–2.6 °C RMSE for the four overpass times of Terra/Aqua. The models based on Terra LST showed higher accuracy than those based on Aqua LST, and nighttime air temperature estimation had higher accuracy than daytime. The seasonal analysis shows daytime CUHI is strongest in summer and weakest in winter, while nighttime CUHI is weakest in summer and strongest in autumn. The annual mean daytime CUHI during 2000–2013 is 1.0 and 2.2 °C for Terra and Aqua overpass, respectively. The annual mean nighttime CUHI is about 1.0 °C for both Terra and Aqua overpass. The resultant CUHI climatology maps provide a spatiotemporal quantification of CUHI with emphasis on temperature gradients. This study has provided information of relevance to urban planners and environmental managers for assessing and monitoring urban thermal environments which are constantly being altered by natural and anthropogenic influences.
Highlights
Urbanization has accelerated in the recent past and is likely to accelerate further in the coming decades
We used the spatially continuous air temperature estimated from Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) to produce the canopy layer urban heat island (CUHI) climatology maps, which improved the spatial coverage compared to traditional measurements from meteorological stations and provided the detailed CUHI spatial extent for urban planning and management
A long-term (2000–2013) monitoring of seasonal CUHI from MODIS data is analyzed for Shanghai in eastern China
Summary
Urbanization has accelerated in the recent past and is likely to accelerate further in the coming decades. UHI has caused significant impacts on environmental quality and human well-being in urban areas, prominent among which include the increase in energy consumption for cooling [4,5], elevation in air pollutant concentrations [6], exacerbating heat waves which cause serious human discomfort and related health and mortality problems [7,8,9], inducing local or regional climate variability and change [10,11], and the increase in urban carbon footprints [12] These adverse effects are even more pronounced in metropolitan areas, especially where there is an ever increasing population density and extensive anthropogenic activities. Studying the spatiotemporal characteristics of UHI has been of great importance to improve our understanding of the intra-urban and inter-urban temperature distribution, the vulnerability to heat risk of urban human populations, and human-environmental interactions [13,14]
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