Investigation of Urban Thermal Island Based on Information of Urban Meteorological Stations

Investigating the micro-climatic conditions of the city based on data from professional meteorological stations reveals more tangible realities from the urban heat island. In this study, urban heat island was analyzed based on hourly and daily temperature data of automated air-polluting stations under the supervision of Isfahan Municipality's Air Monitoring and Control Center. The validity and accuracy of the data of these stations were confirmed by the correlation and graphical test with the data of the Meteorological Organization's ozone meter station at 99% confidence level. Then the thermal island of the city was obtained based on the temperature difference between the urban and suburban surfaces. The results showed that the annual mean of the thermal island was UHIA = -1.27, indicating no thermal island formation at the annual scale. The minimum heat island in summer is UHIS = -1.55 and the maximum in winter is UHIW = 0.96. Thus, only in winter the average temperature in the city is higher than in the suburbs. Investigation of circadian temperature regime at urban and non-urban levels showed that city temperature at night is higher than the peripheral environment due to higher concentration of urban pollutants due to lower night temperature and temperature inversions especially in cold season. However, due to the reflection of more urban surfaces, the surface temperature of the city is lower than the surrounding environment. Thus, the urban island occurs seasonally in the cold season and in terms of day and night changes. Locally, the isotherm of the urban thermal island is denser and more prominent, mainly in the east and northeast of Isfahan, and the center of the thermal island is concentrated in the northeast of Isfahan.