摘要
陕南秦巴山区自然地理和地质条件复杂,受一定的地质地貌、地层岩性、降水、人类活动等多因素相互影响,成为我国地质灾害多发地区之一,而绝大部分地质灾害主要是由强降雨引发的。本文通过对陕南突发性暴雨和连续强降水引发的地质灾害与强降水关系的分析,结合秦巴山区地质灾害风险区划,采用日综合雨量与地质灾害风险耦合的预报预警模型,对2010年7月中旬和2011年7月上旬发生在陕南秦巴山区强降水诱发地质灾害个例进行了检验,该预报模型对这两次地质灾害的落区均做出了准确预报,并给出了4级以上的预警级别,预报效果良好。主要研究结果如下：
1、本文从降雨和地质灾害统计特征分析入手,探讨了当日降雨强度、前期降雨强度、前期降雨日数、持续时间、未来降水预报等因素与地质灾害的关系;在地质灾害风险区划的基础上,建立了日综合雨量与地质灾害风险耦合的预报预警模型、地质灾害气象预报预警判据,同时还给出了不同区域降雨对地质灾害的影响系数。
2、2010年7月中旬和2011年7月上旬的两次暴雨分别代表了连续强雨型和短临强雨型两种诱发地质灾害的暴雨。在这两次地质灾害的预报预警中,耦合的地质灾害预报预警模型分别提前12h和3h以上对灾害发生区域的地质灾害级别做了预报和预警。
3、强降水极易诱发地质灾害。因此,对降雨型地质灾害的准确预报预警首先取决于对暴雨天气形势和雨量的准确预判和预报,必须从诱发地质灾害的暴雨天气的成因和机理进行分析。本文在对2010年7月中旬和2011年7月上旬的两次暴雨进行分析的基础上,得出如下结论：
(1)2010年7月中旬连续暴雨发生的关键因子是近海台风活动和登陆的远距离影响及7月中旬相对稳定维持的东西向带状副高。大暴雨的水汽是由登陆后的台风低压环流东侧的偏南急流来输送,该输送带经向性十分明显,几乎为一致的南风急流,且700hPa表现最为显著。南亚高压的脊线北侧所形成的辐散场与高空急流入口区右侧的辐散场叠置,两个独立的次级环流的上升支重合在一起,有利于深对流天气及中小尺度的发生和发展；暴雨落区位于200hPa高空急流右侧转为西南风的辐散区。700hPa流场表明从南海到陕西建立起由东南风转成西南风的弯曲的水汽通道,把大量的水汽从南海输送到陕西,在偏南风(急流)的前部产生辐合上升,在水汽通量的高值区产生辐合,由此造成暴雨。湿焓分析表明700hPa从台风中心附近至陕西建立了温湿能通量的能量输送通道,把台风中心附近的温湿能向陕西输送,暴雨位于850hPa温湿能等值线密集处。
(2)2011年7月上旬连续暴雨天气形成的大气环流形势具有陕西夏季典型的突发性暴雨的环流特征。主要影响系统是贝加尔湖到新疆北部冷涡底部分裂的冷空气和高原浅槽携带的冷空气东移南下与副高西北部的西南暖湿气流在陕西南部焓交汇所致。暴雨区与低涡切变的位置对应较好,低涡切变是暴雨的直接影响系统。高低空系统的配置有利于汉中地区产生强降水。干线与地面辐合线触发产生对流,是十分重要的触发系统。强降水出现在MCC的强盛期,发生在MCC的TBB北边界的等值线密集区。西北路冷空气南扩明显,对这次暴雨起到触发作用。
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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