| Liangshan is one of the places for serious geological disasters in Western Sichuan,mainly for landslide and debris flows, especially the strong precipitation as the maincause of debris flows are enormous, which often cause severe casualties and economiclosses. So the forecast and early warning of disaster is the most important issue neededto be solved. Through the analysis of debris flow cases from2006to2011, and of theheavy rainfall observation data and the corresponding radar echo information, we havebeen doing the research on the debris flow and precipitation temporal and spatialdistribution in Liangshan as well as the radar echo characteristics and short-timeforecast&warning signal technology. And the main conclusions are as follows:(1) The statistical features of debris flows and the relevant analysis on heavy rainfallin Liangshan. Basing on the geological disaster cases information of2006-2011fromthe Land and Resources Bureau of Liangshan, we preliminarily analyzed thedistribution of debris flow in this area. In Liangshan, the debris flows are mainly causedby heavy rain, and also showed the characteristics as mass, large, medium and smallkinds of disasters. At present2,639the potential points of geo-disasters,53prefecturelevel dangers and20provincial level dangers have been found here in Liangshan. And1176debris flow gullies have been found within the territory of Liangshan. The JinshaRiver, the Yalong River, the Anning River and the Heishui River are the most activeplaces for debris flows. Mountainous regions at moderate and low altitude are morelikely developed to be the places for debris flows. By analysis on the geological disastertype and the time, spatial distribution regularities in Liangshan, it is found that: theLiangshan debris flows outbreak time and places and the main flood seasonprecipitation time and places from May to September are basically the same. Themaximum peak is from June to August, following by May and September, among whichfrom night to midnight is the most possible time for outbreak. Because the disaster often happens at night, the requirements for protection are more complicated.(2) We have done research on the characteristics of radar echo signals and theshort-time forecasting and early warning technology for different level of debris flows.We have collected the Doppler radar echo data of2006-2011debris flow cases,analyzed the characteristics of radar images above and near the places of debris flows,screened on local strong precipitation factors with obvious instructing significance, anddone research on the characteristics of radar echo signals and got the short-timeforecasting and early warning technology for different level of debris flows. First of all,by identifying the radar echo categories, center maximum intensity, mean40dBzintensity area, height, move, strong precipitation accumulation time, precipitationaccumulation time and other information on the occurrence of mass, large, medium,small debris flows, three important factors of partial heavy rain with instructingsignificance are screened: the strongest echo intensity, echo height, strong precipitationecho duration. Secondly, combining the bottom level of the potential points ofgeo-disasters information, according to radar echo signal intensity characteristics, thedebris flow occurrence and radar echo signal correlation are analyzed. The index ofradar echo signals of different levels of debris flows have been gotten. When the uppersky over the disaster points appear echo intensity is of60dBz, and of10.9meters heightand the strong echo persistent descending water time is173minutes, the medium andabove or group debris flows occur easily.(3) The short-time early warning system of debris flows in Liangshan is built basingon the radar echo signal and the GIS technology. Relying on radar echo signal index ofdifferent levels of debris flows and the GIS technology, combined with already-builtdata bank of potential disaster point in Liangshan, we have established the short-timeearly warning system of debris flows in Liangshan, which is basing on the radar echosignal and the GIS technology. By this way, the fast efficient implementation of multipledepartments is provided and the technology of disaster prevention is passed forward tothe grassroots organizations of county, township, village and group so as to greatlyenhance disaster prevention and mitigation, emergency response capabilities, which isof great significance to the geological disasters prevention in Liangshan.(4) The research on the forecast and early warning of debris flows in the blind area ofradar echo. Due to the block of the Luojishan mountain, the territory of45.18°-150.15°in Liangshan becomes the blind area of echo, where there is no echoimage. Through the analysis of the meteorological causes of "7.14","7.31" debris flows,the thought comes out for the meteorological model of the blind area of echo. When it is 500hPa, there will be high pressure tank, West Sichuan low trough (shear), plateau shear;while for700hPa, there will be the water vapor continuous conveying characteristics ofrich southwest warm wet air current. In Liangshan area there is high unstable energywhich is in ascending motion area, high level divergence, low level convergence,relative humidity at90%and above, and the vertical velocity is less than zero, while thepseudo equivalent potential temperature, CAPE index and K index are large. When thegeneral K index is above35and even up to40-45, it is very easy to generate local partstrong precipitation and the debris flows are more likely to happen as well. |
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