Asymmetric changes in maximum and minimum temperature in Beijing

SummaryBased on observational data at Beijing since 1940, trends in daily maximum, mimimum and mean temperatures are studied. It is shown that the linear rate of increase in minimum temperature is 4.08 °C/100 yr; whereas the maximum temperature decreases with a linear rate of — 0.245 °C/100 yr. Consequently, the diurnal temperature range (DTR) becomes smaller.Warming in Beijing occurred mainly in the daytime in the 1940s; but in the night in the 1980s. Although the latter has been found in other studies, the former is a new discovery. The difference of temperature and the diurnal temperature range between urban and surburban areas in Beijing are also analysed. The results show that the urban heat island effect (UHIE) has been becoming larger, and during 1960–1989 the change in UHIE in summer is larger than that in winter. Since the warning trend does not match the change of UHIE in last two decades, it is thought that UHIE is not the main factor contributing to climatic warming.