The Rainstorm Characteristics And Rain Island Effect Evolvement Rule In Chinese Large Cities

The wide and frequent occurrence of rainstorm in cities causes serious effects on socialeconomy and urban safety in China. The urban rainstorm characteristics, the evolvement rules andthe research of rainfall distribution with rain island effect are three important segments in urbanwaterlogging prevention and control capacity.This research aims at the analysis of hourly rainfall in recent years of forty-four sites in thirty-six typical cities in China by comparing urban rainstorm characteristics and evolvement rules. Therainstorm background information index and variation index are used to cluster the cities, andmoreover, the urban rainstorms are separated into nine categories according to meteorological leveland duration grades. In analysis of the characteristics of rainfall patterns and the evolvement rules,six types of short, long and extra-long duration of rainstorm index are applied. In addition, theresearch combines urban buffer area with areal rainfall to analyze the impact of rain island effect onurban rainfall distribution in growing period.(1) The trend of rainstorm level in Chinese typical cities coincides with the features of nationalrainfall distribution: the rainfall decreases gradually from Southeast to Northwest China, and therainstorm level in urban areas is higher than or equal to suburbs in local areas.(2) The level of rainstorm variation in urban areas is higher than the suburbs in typical cities.In addition, the larger city size it is among adjacent cities, the higher level of rainstorm variation ithas.(3) The main type of rainfall in typical cities is long duration rainfall, except the higheroccupation of short duration rainfall in northwest China and extra-long duration rainfall in east,central and southwest China. Moreover, heavy rainstorm and extraordinary rainstorm in southern,eastern and central part of China account for a higher proportion.(4) More cities enjoy ascend trend in rainstorm frequency on different levels and durations in eastern, northern, southern and central part of China. In comparison, a higher number of cities insouthwest China have an increasing trend in rainstorm frequency, but the duration does not changemuch. However, less cities enjoy ascend trend in rainstorm frequency on different levels anddurations in northeast and northwest China, and even worse, the index in Tianjing, Laoshan andChangsha present a descend tread.(5) The short duration rainstorm presents an increase amount in peak precipitation on a largescale. Comparatively, the key point and the peak value in rainfall bring forward in long durationrainstorm, and the variation of rainstorm duration has no significant relations with rainstorm keypoint and peak value but still appear a descend trend on a large scale. In addition, the extra-longrainstorm has no obvious unifying changes on a large scale.(6) The impact of rain island effect on urban rainfall in growing period is geographicallydifferent in Chinese typical large cities. The rainfall concentrates mainly in rural area in southeastand central cities, while in southwest plateau area, northwest China and Semi-arid areas of northChina, the rainfall mostly happens in urban areas.