Abstract:

Urbanization under local climate change often has a significant impact on the occurrence and development of heavy precipitation. In order to explore the role of urbanization and thermal environment on heavy precipitation in Kunming, the hourly precipitation data of Kunming station in the urban area and Jinning station in the suburban area during the wet season (May to October) from 1991 to 2021 were used for analysis. On the basis of revealing the difference and change trend of heavy precipitation at urban and suburban stations in different urbanization stages, combined with MODIS land surface temperature remote sensing image data, further exploration was made on the spatio-temporal distribution of urban thermal environment and its quantitative relationship with urban heavy precipitation in the daytime and nighttime during the wet season in the main urban area of Kunming. The results are as below. In the past 31 years, the heavy precipitation amount (HPA) and heavy precipitation frequency (HPF) at urban and suburban stations have shown an upward trend. Among them, the overall growth rate of HPA and HPF in urban areas is greater than that in suburbs, with significant differences between urban and suburban areas. The contribution rates of urbanization to HPA and HPF in urban areas reach 47% and 40%, respectively. Since the beginning of the 21st century, the total precipitation in Kunming urban area has decreased, and the contribution rate of HPA and HPF in the urban area has been continuously increasing, with their linear trends showing higher significance during the rapid urbanization stage. The heavy precipitation in Kunming urban area is mainly active from 19:00 to 05:00, belonging to a single peak pattern with a nighttime activity. The peak of heavy precipitation occurs at 04:00, and the “night rain” characteristic is significant. HPF has the main contribution to HPA. During the period from 1991 to 2021, there was no significant trend in heavy precipitation at urban and suburban stations during the daytime, while the contribution rate of heavy precipitation and frequency at night at urban station showed an upward trend, which was significant in the rapid urbanization stage of the past 17 years. From 2005 to 2021, the nighttime urban thermal environment index significantly increased compared to the daytime, indicating a significant urban thermal effect. Through correlation analysis, it is found that the urban thermal environment has a positive promoting effect on heavy precipitation in urban areas, and the high significance of this effect is mainly manifested at night.

Key words: Urban thermal environment, Urban heat island, Urbanization, Heavy precipitation, Main urban area of Kunming