Abstract:

Shaanxi Province is located in the northeast of the Tibetan Plateau, which is dominated by complex terrain of the Qinba Mountains, river valley and the Loess Plateau. Rainstorms are frequent and intense in Shaanxi, and often lead to floods and secondary disasters. Based on data of direct disaster reports from 2008 to 2023, this paper analyzes the spatial and temporal distribution of rainstorm floods and secondary disasters. Taking the disasters in the Qinba Mountains area as an example, this paper explores the triggering mechanism of heavy precipitation on extreme floods and secondary disasters. The results are as follows: (1) The frequency of rainstorm and flood disasters and their secondary disasters in Shaanxi Province decreases from south to north. Hanzhong and Ankang in the hinterland of the Qinba mountainous area are high-risk areas for disasters, followed by Shangluo in the eastern section of the Qinling Mountains and Yan’an in the Loess Plateau. (2) The heavy rainstorms and floods in Shaanxi Province occur mainly from July to August, and there are significant inter-annual variations, and 2013 was the year with the most frequent and severe disasters in recent years. (3) Intense and persistent heavy rain is the root cause of secondary disasters such as floods and mudslides in the Qinba mountainous area. The synoptic meteorological analysis of historical disasters indicates that the combined influence of the westward developing of the subtropical high in the middle troposphere and the eastward movement of the mid-latitude trough has continuously transported water vapor and heat to the Qinba mountainous area, and coupled with the high temperature, high humidity in the lower layer and the instability of convection, leading to the continuous occurrence of heavy rainstorms. The gap terrain of the east-west transition in the Qinba Mountains displays a significant role to increase the precipitation, forming a strong “rain pocket” in the center of rainstorm.The mountainous terrain causes surface runoff to converge rapidly, which promotes landslides and mudslides in Hanzhong and Ankang, as well as strong disasters of the damage of reservoirs and bridges and other secondary disasters.

Key words: rainstorm and flood, secondary disaster, spatio-temporal variations, formation mechanism, Shaanxi Province

摘要：

位于青藏高原东北侧的陕西省，受秦巴山、河谷平原及黄土高原等多种地形综合影响，暴雨频发且强度大，经常遭受洪涝及次生灾害。利用陕西省2008—2023年灾情直报信息数据，分析近年暴雨洪涝及次生灾害时空分布，并以秦巴山区的灾害为例，探究强降水对极端洪涝和次生灾害的诱发机制。研究表明：（1）陕西省暴雨洪涝及次生灾害次数由南向北递减，秦巴山区腹地的汉中和安康是灾害高发区，其次是秦岭东段的商洛，以及黄土高原的延安。（2）陕西暴雨洪涝及次生灾害集中在7—8月，且年际差异大，2013年是近年来灾害最多发和损失最严重的一年。（3）持续性强暴雨是秦巴山区暴雨洪涝和泥石流等次生灾害的根源。对历史灾害的天气学分析表明，受对流层中层副热带高压西进和中纬度低槽东移的共同影响，偏南气流不断输送水汽和热量到秦巴山区，加上低层高温高湿和对流不稳定，导致强暴雨持续；秦巴山区东西过渡的峡口处，地形对降水显著增幅形成的强“雨窝”，是洪涝和次生灾害最多的地方；山区地形使地表径流快速汇聚，促进了汉中和安康的滑坡和泥石流，以及水库和桥梁受损等次生灾害。

关键词: 暴雨洪涝, 次生灾害, 时空变化, 形成机制, 陕西省