Urbanization and city climate: A diurnal and seasonal perspective

Abstract

Over the years, a number of researchers have reported that urban development, as the major land-use change in human history, has a great impact upon the local climate of a city (Landsberg, 1981; Arnfield, 2003). One of the best-known effects of urbanization is the urban heat island (UHI) effect, which develops when rural cooling rates are greater than urban ones (Oke and Maxwell, 1975). Factors that may bring about the difference in temperatures between urban and rural areas include (Kalande and Oke, 1980; Oke, 1982; Grimmond, 2007): • the different thermal (heat capacity and thermal conductivity) and radiative (reflectivity and emissivity) properties of construction materials used in urban development compared to surrounding rural areas, resulting in more of the sun's energy being absorbed and stored in urban compared to rural surfaces; • in urban areas, anthropogenic heat emissions by buildings, air conditioning, transportation and industries, contributing to the development of UHI; • the increase of impermeable surfaces in urban areas, which results in a decrease in evapotranspiration and loss of latent heat from the ground, causing warming there; • the tendency of high-density buildings in urban areas to block the view of the sky and to affect the release of heat as long-wave radiation at night; and • dense development in urban areas, which reduces wind speeds and inhibits cooling by convection.