Recently, a research group of Professor Zhao Kun, School of Atmospheric Science has made new progress in the research about urban effects on the precipitation characteristics. They have their findings published in Advanced in Atmospheric Sciences entitled ” Impacts of Urbanization on the Precipitation Characteristics in the Guangdong Province of China”. The first author is Meng Yan, a postgraduate student. The second author is Professor Johnny Chan, City University of Hong Kong. The corresponding author isProfessor Kun Zhao, and the communication unit is Nanjing University.
Fig. 1. The trend distribution of (a) annual precipitation (units: mm yr−1), (b) precipitation frequency (units: % yr−1), (c) intense rainfall frequency (units: % yr−1), and (d) light rainfall frequency (units: % yr−1) in Guangdong Province during 1981−2015. Gray lines represent urban areas. Warm tones represent a positive trend, while cool tones represent a negative trend. The magnitude of the value represents the extent of the increase or decrease. Only sites that pass the 90% Mann−Kendal trend test are shown.
With the development of urbanization, the combination of the heat island effect, the change of land use type and a large number of aerosols in the polluted air have an effect on the atmosphere, cloud and precipitation in urban areas. Guangdong Province is an area of high level of urbanization in China. Also, it is located in the coastal area, experiencing frequent short-term heavy rainfall events. The existence of the Pearl River Delta urban agglomeration is conducive to the study of the impact of urban effects on precipitation characteristics.
Fig. 2. Time series (brown) and trend (green) of annual precipitation, precipitation frequency, and heavy and extreme precipitation frequency during 1981−2015, averaged for (a) 14 stations in the PRD and (b) 9 stations surrounding the PRD.
Whether precipitation characteristics in Guangdong Province, China, from 1981 to 2015 have changed are investigated using rain gauge data from 76 stations. These characteristics include annual precipitation, rainfall frequency, intense rainfall (defined as hourly precipitation ≥ 20 mm), light precipitation (defined as hourly precipitation ≤ 2.5 mm), and extreme rainfall (defined as hourly rainfall exceeding the 99.9th percentile of the hourly rainfall distribution). During these 35 years, the annual precipitation shows an increasing trend in the urban areas. While rainfall frequency and light precipitation have a decreasing trend, intense rainfall frequency shows an increasing trend. The heavy and extreme rainfall frequency both exhibit an increasing trend in the Pearl River Delta region, where urbanization is the most significant. These trends in both the warm seasons (May–October) and during the pre-flood season (April–June) appear to be more significant. On the contrary, the annual precipitation amount in rural areas has a decreasing trend. Although the heavy and extreme precipitation also show an increasing trend, it is not as strong and significant as that in the urban areas. During periods in which a tropical cyclone makes landfall along the South China Coast, the rainfall in urban areas has been consistently more than that in surrounding areas. The precipitation in the urban areas and to their west is higher after 1995, when the urbanization accelerated. These results suggest that urbanization has a significant impact on the precipitation characteristics of Guangdong Province.
Fig. 3. Time series and trend of (a) annual precipitation amount in 1981−2015 during TC rainfall averaged for 14 stations in the PRD (brown) and 9 stations (green) surrounding the PRD, and those of (b) the difference between urban and non-urban stations (blue).
This work of Kun ZHAO was primarily supported by the National Key Research and Development Program of China (Grant Nos. 2017YFC1501703 and 2018YFC 1506404), the National Natural Science Foundation of China (Grant Nos. 41875053, 41805025, 41475015 and 41322032), the Open Research Program of the State Key Laboratory of Severe Weather, and the 5th “333 High-level Personnel Training Project” of Jiangsu Province (BRA2019037). The work of Meng YAN and Johnny C. L. CHAN was supported by the Research Grants Council of the Hong Kong Special Administrative Region of China (Grant No. CityU 11301417).
Yan, M., J. C. L. Chan, and K. Zhao, 2020: Impacts of urbanization on the precipitation characteristics in Guangdong Province, China. Adv. Atmos. Sci., 37(7), https://doi.org/10.1007/s00376-020-9218-3. (in press)