Abstract
A primary impact of urbanization on the local climate is evident in the phenomenon recognized as the Urban Heat Island (UHI) effect. This urban thermal anomaly can increase the health risks of vulnerable populations to heat waves. The surface UHI results from emittance in the longer wavelengths of the thermal infrared; however, there are also urban anomalies that are detectable from radiance in the shorter wavelengths (3–5 micron) of the Middle Infrared (MIR). Radiance in the MIR can penetrate urban haze which frequently obscures urban areas by scattering visible and near infrared radiation. We analyzed seasonal and spatial variations in MIR for three Central European cities from 2003 through 2012 using Moderate Resolution Imaging Spectrometer (MODIS) band 23 (~4 micron) to evaluate whether MIR radiance could be used to characterize heat anomalies associated with urban areas. We examined the seasonality of MIR radiance over urban areas and nearby croplands and found that the urban MIR anomalies varied due to time of year: cropland MIR could be larger than urban MIR when there was more exposed soil at planting and harvest times. Further, we compared monthly mean MIR with the Normalized Difference Vegetation Index (NDVI) to analyze contrasts between urban and rural areas. We found that the seasonal dynamic range of the MIR could exceed that of the NDVI. We explored the linkage between meteorological data and MIR radiance and found a range of responses from strong to weak dependence of MIR radiance on maximum temperature and accumulated precipitation. Our results extend the understanding of the anomalous characteristics of urban areas within a rural matrix.
Highlights
Among the many transformational anthropogenic activities, perhaps the most striking human impact on the global biosphere is the transformation of Earth’s land surface into urban areas [1].This land cover conversion affects a wide range of processes, including the surface radiation and energy budgets, the water, carbon, and nutrient cycles, soil dynamics, vegetation productivity and phenology, and local and regional biotic diversity [2]
We found that the seasonal dynamic range of the Middle Infrared (MIR) could exceed that of the Normalized Difference Vegetation Index (NDVI)
We explored the linkage between meteorological data and MIR radiance and found a range of responses from strong to weak dependence of MIR radiance on maximum temperature and accumulated precipitation
Summary
Among the many transformational anthropogenic activities, perhaps the most striking human impact on the global biosphere is the transformation of Earth’s land surface into urban areas [1]. This land cover conversion affects a wide range of processes, including the surface radiation and energy budgets, the water, carbon, and nutrient cycles, soil dynamics, vegetation productivity and phenology, and local and regional biotic diversity [2]. A primary impact of urbanization is on the local climate at multiple temporal scales. The structure of the urban built environment shows increased impervious surface area and more aboveground mass with higher thermal storage capacity than rural environments. Urban areas are usually warmer than nearby rural areas, a phenomenon recognized as the Urban
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