Analysis of precipitation characteristics over Hefei district in summer based on TRMM PR

In order to study the urbanization impact on precipitation and explore the corresponding effect mechanism, the characteristics of convective and stratiform precipitation are investigated based on measurements of the TRMM Precipitation Radar over Hefei in summer (June, July, August) during 1998-2012. The results show that the development of urbanization significantly affects the spatial distribution of precipitation with higher convective and stratiform precipitation rate over the urban area and lower value over the rural area. Moreover, convective precipitation frequency is lower in the urban area than over the rural area, while stratiform precipitation frequency is higher over the rural area. In addition, the vertical structure of precipitation shows that the precipitation echo top over the urban area is higher than that over its surrounding rural area, which reveals that urbanization is conducive to the development of precipitation system but suppresses precipitation rate over the urban area. Consistent with the urban heat island diurnal variability, there is an increase in the rate and frequency of convective precipitation in the urban area during afternoon and nocturnal hours, while there is no significant diurnal cycle in the rural precipitation. In general, urbanization has a great impact on local precipitation rate, while the effect on local precipitation frequency is not significant. The long-term trend in precipitation shows that the rate and frequency decline over the urban area, while there is an upward trend in precipitation rate and a declining trend in precipitation frequency over the rural area. Additionally, the difference in precipitation characteristic between urban and rural areas becomes significant due to the urbanization. By analyzing the distribution of extreme precipitation, it is found that strong precipitation frequency over the urban area is lower than that over the rural area. In particular, it is 75% lower than that in downwind of the city, whereas weak precipitation frequency in the urban area is higher than that over the rural area and 18% higher than that in the downwind area.