Day-of-the-week variations of urban temperature and their long-term trends in Japan

Temperature differences among days of the week and their long-term trends were evaluated using 29 years of hourly data from the Automated Meteorological Data Acquisition System network of Japan. Stations were categorized with respect to the population density around each site, and an urban temperature anomaly (δT*) was defined as a departure from the spatial average of nearby rural stations. On Saturdays and holidays (Sundays and national holidays), δT* was lower than on weekdays by 0.2–0.25°C at Tokyo, by 0.1–0.2°C at Osaka, and by about 0.02°C at stations where the population density was 300 to 1,000 km^–2. Moreover, δT* showed a relative decreasing trend over the long term on Mondays and an increasing trend on Fridays, at a rate of about 0.05–0.1°C decade^–1 at Tokyo and about 0.02°C decade^–1 at stations where the population density was 100 to 1,000 km^–2, but no significant difference in δT* trends was observed between weekdays and weekend days.