北京市地质研究所, 北京 100120
基金项目: 国家自然科学基金项目(批准号:41772182和41672181)、国家重点基础研究发展计划项目(批准号:2017YFA060340202)和中国科学院(B类)科技先导专项项目(批准号:XDB26020000)共同资助
详细信息
作者简介: 王海芝, 女, 45岁, 高级工程师, 地质环境调查评价及地质灾害预报预警, E-mail:418424101@qq.com
中图分类号: P642.23;P694 收稿日期:2020-03-21
修回日期:2020-06-06
刊出日期:2020-09-30
Early warning thresholds of the rainfall-induced debris flows in Beijing
Wang HaizhiBeijing Institute of Geology, Beijing 100120
MSC: P642.23;P694
--> Received Date: 21 March 2020
Revised Date: 06 June 2020
Publish Date: 30 September 2020
摘要
摘要:泥石流是北京地区主要的地质灾害，强降雨是触发这一灾害的主控因子。因此，触发泥石流临界雨量的厘定成为实现高精度预报预警和防灾减灾的关键。但是，以前的研究多基于简单数据统计或定性分析层面，远不能满足地质灾害预警需要高精度定量数据的要求。文章对1949年以来北京地区发生的泥石流与其发生时期的降水数据进行了系统收集整理，对降雨强度-降雨持续时间和降雨量-降雨持续时间的泥石流触发临界值进行了高分辨的分析和厘定，首次建立了临界雨量的定量估算模型，分别为Ι=56.9×D-0.746与R=59.9×D0.253。通过与全球其他地区的临界阈值模式对比发现，在降雨持续时间较短时，北京地区的临界雨量高于全球性和一些区域性临界雨量，而随降雨时间的增加，全球范围内的临界雨量具有收敛趋势。这表明不同地区的临界雨量，特别是短时暴雨触发的泥石流，需根据区域特征来厘定。随降水时间的增加，区域地质地貌的影响会逐渐减小，而降水的控制作用会逐渐明显。北京地区泥石流发生时期降雨持续时间与降雨强度和总降雨量之间相互关系表明，泥石流的发生不仅需要较大的降雨强度，而且需要一定的降雨量。因此，北京地区地质灾害预警应综合利用两种临界雨量模式。
关键词: 泥石流/
临界雨量/
降雨强度/
降雨时长/
北京地区
Abstract:As urban populations and infrastructure have increasingly expanded into debris flow-prone areas in Beijing, the risk of losses and fatalities from debris flows has increased. As a result, the significance in debris flow early warning, as a way to reduce losses, injuries, and especially fatalities, has been increased substantially. To analyze the primary causes of flow debris and make an accurate warning, it is necessary to understand the relation between rainfall and the initiation of flow debris, as abnormal high precipitation is often the trigger of debris flows. Therefore, the rainfall threshold for debris flow initiation has become the key factor in understanding the dynamics of debris flows and the accurate forecast and warning. However, there are few quantitative research and far from the requirement for accurate early forecasting and warning of debris flows in Beijing.
To constrain the rainfall threshold of debris flow in Beijing, we collected the data of the past rainfall-induced debris flows with accurate precipitation registers. Based on these data, this study made the first comprehensive analysis and established the rainfall thresholds of the debris flows in Beijing. The specific achievements are as follows:
A total of 49 events with accurate precipitation registers have been collected, which occurred during the interval from 1949 to 2012. All of the debris flows occurred in the mountain area, most of which concentrated in central and northwestern Huairou, northern Miyun, southwestern Mentougou, southwestern and northwestern Fangshan districts, and several events in Yanqing and Pinggu districts. The frequency of debris flows was much higher during the interval from 1949 to 1972 than that after 1972 with only one event (2012) after 2000.
All of the debris flows occurred from June to August during past 70 years, which corresponds to the maximum precipitation season of a year in Beijing. The debris flows of July and August account for 51% (25 evets) and 35%, (17 events), respectively.
Both the amounts and the durations of the precipitations causing debris flows displayed a large variations during past 70 years. The rainfall amounts ranged from 115 mm to 668 mm, and the durations changed from 1.5 to 168 hours. Low duration precipitation (< 1.5 hours) rarely caused debris flows.
The experimental models of rainfall thresholds were established based on the relationship of rainfall duration (D) with rainfall intensities (I) and cumulative rainfall (R) (I=56.9×D-0.746 and R=59.9×D0.253), respectively. Both the cumulative rainfall and intensity threshold display some power to identify rainfall conditions that are likely to trigger debris flows, but either one alone might not be adequate to characterize the comprehensive rainfall threshold conditions. Consequently, the warning scheme should use the two thresholds in tandem and uses the reduced value, particularly when antecedent wetness is high.
The rainfall thresholds of Beijing show a large difference from those of the global and some regional/local models when the rainfall durations are small (< 3 hours). However, the thresholds show a convergent trend with increased duration of rainfall across the globe. This characteristic suggests that the contribution of rainfall would increase with enhanced rainfall duration. Moreover, the experimental rainfall thresholds of the debris flows under short rainfall duration condition show a large deviations from one place to other across the globe. Therefore, regional/local thresholds should be recalibrated by regional/local data, particularly for the debris flows caused by short-tern intensive rainfall.
Key words:debris flow/
rainfall threshold/
rainfall intensity/
cumulative rainfall/
rainfall durations
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