Abstract:The single-factor analysis and multi-factor comprehensive evaluation delineation method are used to evaluate the geo-disaster prone area, and the rainfall distribution characteristics and the frequency of geo-disasters are combined to determine the geo-disaster meteorological early warning area. Taking the towns and streets as early warning units, and the effective rainfall and activated rain intensity of geological disasters as the disaster-causing factors, the box plot analysis method is used to determine the rainfall threshold index value of all levels of landslide geological hazard. The method of typical heavy rainfall process combined with disaster reverse check and historical typical case back is used to test the rainfall threshold of geological disaster warning. From the statistical analysis of geological disaster census cases in Zhuzhou from 2011 to 2021, it is found that the geological disasters in Zhuzhou are mainly landslide disasters, followed by collapse, and small-scale geological disasters account for 98% of the total. The occurrence period of geological disasters in Zhuzhou is consistent with the rainy season, and landslide geological disasters are mainly distributed in Youxian County and Chaling County, and collapse disasters are mainly distributed in Lusong District and Hetang District. More than 80% of towns and streets in the city have experienced geological disasters. Geological disasters in Zhuzhou are closely related to rainfall, and heavy rain or more is the main factor for the formation of geological disasters in Zhuzhou. When the rain intensity is more than 20 mm/h, the risk of geological disasters in Zhuzhou is relatively high, and the risk of geological disasters induced by heavy rain intensity more than 50 mm/h is great. The critical value of effective rainfall for geological disasters in Liling is 61.9 mm, and the critical rainfall in other counties (cities, districts) is less than 50 mm, and the effective rainfall is more than 80 mm when more than 80% of geological disasters occur. The geological disaster meteorological early warning area of Zhuzhou can be divided into key early warning area A, sub-key early warning area B and general early warning area C. Each early warning area contains N early warning units of towns or streets. The effective rainfall and activated rain intensity are taken as the disaster factors. Using the box plot analysis method, it is clear that the disaster probability of 25% is the yellow warning rainfall threshold, the disaster probability of 50% is the orange warning rainfall threshold, and the disaster probability of 75% is the red warning rainfall threshold. The blue, yellow, orange and red warning rainfall thresholds of landslide-type geological disasters in different meteorological warning zones of Zhuzhou are determined. It is proved that the threshold index of early warning rainfall with effective rainfall as the disaster factor has a good application effect in practical early warning, while the threshold index of early warning rainfall with activated rainfall intensity as the disaster factor is lower and has a larger false alarm rate, so it should not be used alone in practical early warning.
