Effect of land cover on air temperatures involved in the development of an intra-urban heat island

Mobile traverses were used to conduct air temperature observations to clarify the effect of land cover on ambient air temperatures. The study area was located in a suburb of the Tokyo metropolitan area, Japan. The mobile traverses were conducted at 2 h intervals between 10:00 h on one day and 08:00 h the next day, on selected days from October 2006 to March 2008, for a total of 30 d. We observed an intra-urban heat island (IUHI) throughout the year and determined the diurnal and seasonal variations in this IUHI. The daily maximum intensities of the IUHI under calm and cloudless conditions ranged from 4.0 to 6.9°C during all seasons of the years examined. Such large IUHI intensities are determined by clear boundaries between adjacent land covers, independent of a city’s size. The development of an IUHI is related to the features of the land cover, and the causal factors that enhance an IUHI differ between dayand nighttime. In most cases, observed air temperatures varied significantly according to ambient land cover types, and air temperatures decreased as the amount of vegetated area around the sites increased. These land cover effects were slightly stronger at night than during the day, and they weakened as the amount of cloud cover or the wind speed increased, especially at night.