甘肃临夏地区冰雹时空分布特征及其灾害风险区划初探

Analysis of temporal and spatial distribution of hailstorm and its disaster risk zoning in Linxia of Gansu province

利用甘肃临夏州6个气象观测站1968—2013年观测资料,分析了临夏州近46 a冰雹的气候特征。结果表明:临夏州年平均降雹次数分布具有明显的地域特点,受地形因素影响,干旱山区降雹次数多,川塬区较少。冰雹的年代际变化显著,1970s、1980s是降雹的高峰期,1990s至今降雹相对较少。春季开始出现冰雹,秋季结束,夏季降雹频次最大;5月是降雹高峰期,随后呈逐月下降趋势。一日中冰雹天气主要发生在14—21时(北京时,下同),19时左右发生冰雹的概率最大。降雹频次与海拔高度基本上呈线性关系。通过冰雹对农业造成的经济损失影响分析,建立冰雹灾害风险指数评估模型,确定临夏州冰雹灾害风险等级系数,采用风险指数法、层次分析法等数量化方法,借助Arc GIS软件进行栅格图层计算得到临夏州冰雹灾害风险区划图,结果表明:临夏州冰雹风险区划总体上与降雹空间分布相对应,同时受地形特点、社会经济、人口密度和耕地面积比例的影响,由西南部到东北部,由高海拔向低海拔呈递减趋势。

Using statistical method and meteorological data at six stations in Linxia area during the period from 1968 to 2013, in this study we have analyzed the spatial and temporal distributions of the climatological characteristics of hail over a period of 46 years. The results show that the distribution of annual average hail shooting times in Linxia has an clear regional characteristic, i.e., hail occurs more frequently in mountainous terrain than in flat areas due to the influence by terrain factors. Hail occurred the most frequently in the 1970s and 1980s, and less frequently from 1990s to the most recent years. Hail starts to occur in spring, and becomes the most frequently in late summer, and ends in autumn. May is the fastigium of hail and then the occurrence of hail decreases month after month. The main hail weather happens at the time of 14:00 BT to 21:00 BT, with the greatest probability of hail occurring around 19:00 BT in a day. There is basically a linear relationship between the number of occurrence of hail and the altitude. Through analyzing the influence of hail on agricultural economy, a model has been established on the basis of an estimation of the risk index in hail damage, and the risk coefficient of hail damage is determined by a series of quantitative algorithms, such as risk index, analytic hierarchy process (AHP) with technique and Raster Layer calculator in ArcGIS. Then the comprehensive risk zoning map of hail damage in Linxia is able to be achieved by conducting the approaches reported above. The results reveal that the risk zonation of Linxia matches the spatial distribution pattern of hail damage comparably optimal as a whole. As the effect of topography,socioeconomic, population density and the ratio of arable size on hail, it leads to a decreasing tendency of hail risk from southwest to northeast with altitude declining.