重庆市2022年8月森林火灾火烧区特点及火后泥石流易发性评价

Characteristics of burned area and susceptibility assessment of post-fire debris flow of Chongqing wildfire in August,2022

2022年8月重庆市江津区、巴南区、北碚区相继爆发森林火灾,总过火面积约35 km^(2)。火灾后火烧迹地植被及土壤结构遭到破坏,坡表堆积了厚度1~5 cm不等的灰烬层,受强降雨影响一旦爆发火后泥石流,将对附近村镇基础设施及群众生命财产构成严重威胁。通过遥感解译、现场调查及试验,查明了本次森林火灾火烧区空间分布特征,实测了火烧迹地灰烬层厚度、土壤饱和导水率等参数。结果表明研究区重度、中度和轻度火烧区分别占9.6%、34.0%和56.4%,其对应的坡面灰烬-结构扰动层平均厚度分别为5.10,3.28,1.15 cm。基于专家经验预测模型对火烧区共95条潜在泥石流沟道进行火后泥石流易发性评价,其中1条为高等易发,43条为中等易发,44条为低等易发,7条为不易发,分别占总数的1.05%、45.26%、46.32%、7.37%。考虑到现状条件下各泥石流沟域内中度和重度火烧区仍残留有大量灰烬、泥沙等松散固体物源,且土壤表现出较强的斥水性,中等及高等易发性沟道在雨季一旦受集中降雨影响,爆发火后泥石流的可能性较大。研究成果可为火烧迹地火后泥石流灾害预防与风险管理提供科学依据。

In August,2022,forest fires occurred in Jiangjin District,Banan District,and Beibei District in Chongqing,respectively,with a total burned area of approximately 35 km^(2).After the wildfire,an ash layer with a thickness of 1~5 cm was deposited on the slope,and the vegetation and soil structure of the burned area were devastated.Affected by concentrated rainfall,it will pose a serious threat to the infrastructure of nearby villages and towns and residents’lives and properties once the post-fire debris flow occurs.Based on the remote sensing,field investigation,and in-situ tests,the distribution characteristics of burned areas after the fire were identified.The measured data including the thickness of the ash layer,and the saturated hydraulic conductivity of the soil were derived.The severe,moderate,and low burned areas accounted for 9.6%,34.0%,and 56.4%of the entire area,respectively,with the corresponding average thickness of ash and soil disturbance layer of 15.10 cm,3.28 cm,and 1.15 cm.According to the prediction model based on expert experience,a total of 95 potential debris flow gullies in burned areas were evaluated for the susceptibility of post-fire debris flow,of which 1 was of high susceptibility,43 were of medium susceptibility,44 were of low susceptibility,and 7 were not prone to occur,contributing to 1.05%,45.26%,46.32%,and 7.37%of the total,respectively.Considering that a large number of loose solid sources besides ash and sediment still exist in the moderate and severe burned areas within watersheds under the current conditions,with strong water repellency of burned soil,once the medium and high susceptibility gullies are affected by concentrated rainfall in the rainy season,there is a relatively high probability for the post-fire debris flow occurrence.This study provides basic information for the prevention and risk management of post-fire debris flows.