| The natural geographical and geological conditions are complicated in Qinling and Bashan mountains of Southern Shaanxi. Due to mutural interaction and restraint of certain geological, stratigraphic-lithologic physiognomy, precipitation and human activities, it is one of the most vulnerable areas of China prone to geological disasters, in which a majority is intrigued by strong precipitation and flooding. Using a coupled predicting model of daily comprehensive rainfall and geological disastrous risk, combined with geological disastrous risk regionalization of Qingling-Bashan mountainous region, we analyzed the relationship of strong precipitation and geological disasters induced by consecutive strong precipitation in southern Shaanxi. Two consecutive precipitation events of the target area were selected to verify the predictability of this model, occurred in the second ten days of July, in2010, and the first ten days of July, in2011respectively. The model gave a good result that in both case, the potential spots of geological disasters were predicted and rated level4+.1. In this study, the precipitation and geological disaster features are analyzed. For precipitation, factors as intraday precipitation intensity, pre-precipitation intensity, pre-rainy days, rain duration and future precipitation prediction are considered. A pattern of torrential rain causing geological disaster is worked out. Based on geological risk regionalization, we developed a predicting and warning model of daily precipitation coupled with geological disaster risk, and created a meteorological predicting criterion of geological disasters which could come out with influence index of precipitation in different areas.2. In case study of two rain events of the target area occurred in the second ten days of July, in2010, and the first ten days of July, in2011,which represent consecutive heavy rain and short-term heavy rain in respective, the coupled model gave out forecast result of geological disaster rate for the target area12hours and3hours in advance respectively.3. Geological disasters are induced by heavy rainstorm. Hence, an important predicting proof of such geological disaster is a precise judgment and forecast of the torrential rain conditions. It is important to study the causation and mechanism of this type of torrential rain. Based on the above two case studies, the following conclusions are drew out.(1) In the second ten days of July, in2010, the key factor of the torrential rain occurrence is inshore typhoon activity and a long-distance influence of its landing, and a relative stable maintenance of east-west stretched subtropical anticyclone in mid-July. Water vapor of the strong torrential rain was transferred by the partial southerly stream on the east side of the landing typhoon, which was different from influencing on Taiwan Island. It showed an apparent longitudinal transferring path with an almost accordant southerly jet stream, prominent on700hPa level. Divergent field on the north side of the ridge line of South Asia High was overlapped with the divergent field on the right entrance of high-level jet stream, and upward streams from two independent secondary circulations were in superposition, which was favorable for development of Meso-small scale system and deep convective weather. The torrential rain occurred in the divergent area on the right side of northwesterly jet stream on200hPa level. Water vapor on700hPa showed a curved transferring path formed by southeasterly and southwesterly wind from South Sea to Shaanxi, which brought a large amount of water vapor to Shaanxi from South Sea, ascended upward in the front of the partial southerly jet stream, converged in the high value area of water vapor flux and in consequence, caused torrential rain. Moist function analysis showed an energy transferring path of warm moist energy flux from the adjacent area of typhoon core to Shaanxi. The torrential rain occurred where isograms of warm moist energy value concentrated on850hPa level.(2) In the first ten days of July, in2011, circulation patterns of consecutive torrential rain were recognized as a typical abrupt torrential rain weather patterns in summer of Shaanxi. The pivotal affecting mechanism is the enthalpy intersection in southern Shaanxi of the cold air split from the bottom of the cold vortex located between Lake Baikal and north of Xinjiang with cold air carried by shallow trough moving southeastwards from the Tibet plateau, and warm moist air from the northwest part of the subtropical High. The torrential rain area was well corresponded to the position of the low vortex, which is the direct affecting system. The copulation of systems on upper and lower levels is favorable for torrential rain occurrence in Hanzhong. The dry line and convergent line on ground surface contributed to convection which can be the important triggering system. The strong rain occurred on mature stage of MCC, in the north side of the MCC where isograms of TBB value were concentrated. Cold air from northwest moved obviously towards the south, which intrigued the torrential rain. |
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