Hail Distribution and Topographical Factors in Guizhou Province Based on GIS Technique

Research on the relationship of topographical factors to distribution of hail, and getting an image of subdivisions for hail hazard which quantificationally concerns the difference of topographical factors are important to hailweather forecasting.Also, best services for decision-making to disaster prevention and reduction is provided.The relationship between distribution of hail and some topographical factors, such as elevation, slope grade, slope aspect and terrain incision depth, are studied by using GIS techniques, such as digital terrain analysis, zonal statistics and image classification with historical hail records of 84 meteorological stations over 44 years inGuizhou Province and the 1:1000000 resolution DEM data of China.It shows that natural logarithm of meanannual hail days conforms to normal distribution.The elevation is the major topographical factor which primarilyinfluence the distribution of hail, the annual mean hail days increase with the increase of elevation and it increases remarkably as the elevation increases to about 1000—1500 meters.Micro topographical factors, such as slopegrade and slope aspect, are not remarkable factors to the variance of annual mean hail days, but topography rising over large area and windward slope of warm moist air are favorable to hail. Terrain incision depth is not remarkable factor to the difference of annual mean hail days either.Different latitude is also one of the factorswhich influence the difference of annual mean hail days.The model for annual mean hail days derived from thethree remarkable factors and the map of hail hazard evaluation are reliable via statistical test and comparison tohistorical hail reports over countryside spots.The analysis is influenced due to the lack of hail reports in inner mountainous area in Guizhou and the incomplete collection of hail reports data.The relationship between different topographical factors should be further studied.