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

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.