Changes of Comfort Index over Beijing in Recent 15 Years Based on Automatic Station Data

The effective temperature in Beijing has been studied by the entire available observation data. The results demonstrate the following: 1) The annual temperature, wind speed, and effective temperature in Beijing were significantly affected by the topographic distribution, without a significant difference in the relative humidity between the mountainous and the urban areas. Beijing became drier and warmer over the study period. Regionally, the stations with the largest increase in the annual and effective temperatures were concentrated in the urban areas, and the stations with the smallest increase were located in the northwest and northeast mountainous areas. Relative humidity decreased evenly across the entire area of interest. 2) According to the thermal grades of effective temperature, the temperature of winter belonged to “very cold”, that of the annual average, spring, and autumn belonged to “cold”, and that of summer belonged to “warm”. The area became dryer and warmer in the spring, summer, and winter. However, in autumn, the regional temperature difference was obvious. 3) The “weather-friendly” days in Beijing accounted for 41.3%, with large regional differences. Over half the sites showed a reduction in the number of “weather-friendly” days. The “weather-friendly” days in spring increased in number, while those in summer decreased, without any consistency in autumn. In winter, there were nearly no “weather-friendly” days, just “very cold” and “cold” days.