Abstract:

Abstract:The relationship between urbanization and spatial-temporal distribution of rainstorms, and effect of urbanization on variation characteristics of heavy rain in Taiyuan were studied based on urbanization factors and precipitation data of 7 national meteorological stations in Taiyuan from 1981 to 2016, and temperature, precipitation data of 59 regional meteorological stations in Taiyuan during 2008-2015.The results are as follows: (1) There was obvious local and inter-decadal characteristics of heavy rain in Taiyuan in recent 36 years. Rainstorm days at single station in Taiyuan accounted for 61.4 percent of total rainstorm days. The number of local rainstorms increased rapidly in the 1990s compared with the 1980s. While after the mid of 1990s, the regional rainstorm days increased rapidly, and the scope expanded. During 1980-2010, rainstorm days in urban were more than those in counties, precipitation time was more concentrated, and there was obvious difference of heavy rainfall between the western and eastern in urban areas. (2) There was obviously positive correlation between each development index of urbanization and short term rainstorm, while urban population growth and expansion of space made rainstorms increase dramatically. (3) Urbanization made city center become apparently heat island, and increased temperature gradient between city and county area. The existence of urban heat island made the atmospheric stratification more unstable in central urban than that in other areas. Meso-scale thermal low pressure or boundary layer convergence line generated by thermal forcing were in favor of triggering convection. So it was easy to produce short-term rainstorm and heavy rainfall. Moreover, under the synoptic scale background, the mean turbulence field of the heat island made average thermodynamic stability of boundary layer decrease in the east, while increase in the west of Taiyuan, which was interacted with easterly winds (prevailing wind). The topographic structure surrounded by mountains on three sides in Taiyuan made the temperature gradient between city and mountain area increase, and enhance rain intensity in the eastern part of the city area, and more prone to short term rainstorms. The effect of urban friction make the probability of heavy rain increase by prolonging stay time of weather systems in urban area.

Key words: urbanization, rainstorm, change, influence

摘要：

利用太原1981—2016年城市化发展与7个国家气象站降水资料、59个区域气象站2008—2015年气温、降水资料，分析了城市化与暴雨时空分布变化的关系及其影响机理。结果表明：（1）近36 a来，太原暴雨具有明显的局地性和年代际特征。太原单站暴雨日数占总暴雨日数的61.4%，1990年代较1980年代局地暴雨日数增加较快；1990年代中期以后，区域性暴雨的日数快速增多，范围扩大。1980—2010年代，城区暴雨明显多于县区，降水时间更集中，且城区暴雨东、西部存在明显差异。（2）太原城市化各项发展指数与短时暴雨发生频次均存在显著正相关，而城市人口增长和空间的扩大使得暴雨显著增多。（3）城市化使中心城区成为明显的热岛，城郊间的温度梯度增大。城市热岛的存在，使中心城区大气层结较其他区域更加不稳定，热力强迫在城区产生的中尺度热低压或边界层辐合线有利于触发强对流，从而产生短时暴雨。另外，在天气尺度背景下，热岛平均扰动场通过与偏东风（盛行风）相互作用，使得边界层平均热力稳定度在城区东部减小、西部增加，太原三面环山的地形结构强化了城区与山区间的温度梯度，使得城区东部雨强加大、短时暴雨易发。城市摩擦效应通过延长天气系统在城区滞留时间，也增大了城区暴雨的发生概率。

关键词: 城市化, 暴雨, 变化, 影响