Abstract:

Based on the data of daily mean, minimum and maximum air temperatures observed four times per day in the Anshan region from 1951 to 2017, the change characteristics of the annual, seasonal, and monthly mean air temperatures and extreme air temperatures and their variation ratios as well as the variation of urban heat island were analyzed. The results showed that the increasing trend is strongest for the annual mean minimum air temperature followed by the mean air temperature and is the weakest for the average maximum air temperature in Anshan in the studied period, and all these results have passed the significance test. The annual extreme maximum air temperature in Anshan shows a weak decreasing trend from 1951 to 2017 and experiences a decreasing trend from 1951 to 1987 (before the mutation) and an increasing trend from 1988 to 2017 (after the mutation). Inversely, the annual extreme minimum air temperature shows a significant increasing trend from 1951 to 2017, and a stronger increasing trend from 1951 to 1987 (before the mutation) relative to the former, while shows a decreasing trend from 1988 to 2017 (after the mutation). On the whole, the variations of extreme maximum and minimum air temperatures before and after the mutation are opposite. From 1958 to 2017, urban heat island intensity in Anshan is the largest for annual minimum air temperature, followed by the mean air temperature, and is the smallest for the maximum air temperature with the weakest increasing trend. The intensities of the urban heat island in Anshan in autumn and winter are stronger than in other seasons with a significantly increasing heat island index. Among the four regular temperature observations per day, the intensity of the heat island in Anshan is the smallest at 14 o'clock and the largest at 02 o'clock, and the heat island index shows a decreasing trend at 14 o'clock and a significantly increasing trend at the other times. The mean air temperature in Anshan shows a significantly increasing trend. The intensity of urban heat island and the heat island index in Anshan both increase significantly, especially at nighttime, indicating that the significant increase of the intensity of urban heat islands is one of the main reasons for climate warming in Anshan.

Key words: Air temperature change, Urban heat island, Mutation, Climate warming