Temporal Variability of an Urban Heat Island in Yekaterinburg

The article deals with the analysis of temporal variability of the urban heat island (UHI) in the field of surface air temperatures in Yekaterinburg using the data on meteorological observations on weather stations “Yekaterinburg” and “Verkhnee Dubrovo”. The UHI intensity variations have been analyzed for the periods from annual/interannual to diurnal. The sustainable effect of the urban heat island is manifested in all seasons. Annual cycles of monthly averaged UHI values demonstrates “W”-shaped form with maxima of about 1.0 ºС in February/March and in three summer months. Summer maximum is generally determined by maximal diurnal (night) UHI values. The maximum in February/March is related to the increased minimum daily values. From the 50s of the 20th century “W”-shaped annual curve of the UHI intensity remained unchanged under the increase in mean annual UHI values while growing at a rate of 1.31 ºС/100 years to the beginning of the 80s. At the same time, summer maximum increased at a faster rate in comparison with the winter one. Since the beginning of the 80s, the mean annual UHI intensity has stabilized at the level of 0.8 ºС. In a diurnal cycle, the maximal UHI intensity (to 2.4 ºС) is observed in May-July after the sunset. Maximal daily UHI intensity values in summer months are associated with a slower cooling of the city in high-rise building area. The local afternoon maximum (up to 0.8 ºС) caused by the insolation maximum under low albedo value of the urban coverage occurs also from May to July. In the autumn-winter period and at the beginning of spring, the daily amplitude of the UHI intensity decreases due to a decrease in the maximum of UHI and a slight increase in the minimum one. The increase in the minimum UHI values is facilitated by cloudiness, snow cover, calm wind conditions, an increase in the concentration of aerosol and water vapor near the surface and anthropogenic heat emissions. The study results can be used in fundamental and applied climatology, in the development of urban policy.