基于FFPI模型的甘肃陇南山区山洪灾害风险评价

Risk assessment of flash flood disasters in Longnan mountain area of Gansu Province based on FFPI model

山洪是山区小流域由强降雨引发的突发性、破坏性强的自然灾害,对当地人民的生命和财产安全形成极大威胁。以往的研究多基于单沟或小流域尺度、采用成熟的评估体系和模型。如何在地形多样、地质结构复杂的山区评估山洪灾害仍需进一步探索。以山洪灾害频发的甘肃陇南山区为例,引入山洪潜在指数(flash flood potential index,FFPI)构建评价体系和框架。首先选取坡度、土地利用、土壤质地和植被覆盖度,结合层次分析法与信息熵综合定权构建了研究区山洪潜在指数FFPI的空间分布;其次引入0~24 h累计最大降雨量、雨季日均降雨量和汇流累积量作为驱动因子,国内生产总值GDP、人口密度和道路密度为承灾体,分别获取研究区山洪灾害的危险性和风险空间分布,并与该区历史山洪灾害数据进行验证。研究结果表明:采用耦合FFPI模型对甘肃陇南山洪灾害风险评价的准确率较高,有95.77%的历史山洪灾害数据分布于中、高和极高风险分区。从行政区划分析,研究区山洪灾害高风险和极高风险区主要分布在武都区的汉王镇、成县、康县部分地区,占比分别为31.5%、28.3%和18.1%;低风险区位于礼县、舟曲县和文县部分区域,占其县区比例分别为18.9%、18.4%和13.6%。从流域范围分析,研究区山洪灾害高风险区主要集中在山区地势平缓、人口密度较大、经济较为发达的河流下游地区,低风险区主要集中于地势较高的西部和北部,评价结果与研究区调查的山洪灾害实际情况一致。研究结果可为甘肃省陇南山区山洪灾害防治及相关研究提供参考和理论依据。

Flash floods are often sudden and destructive natural disasters triggered by heavy rainfall in small mountainous watersheds,which cause a great threat to the lives and property safety of local people.Previous flash flood studies are mostly based on single ditch and small watershed scales with mature assess system and models.How to assess flash flood hazards in the large-area mountain with diverse landforms and complex geological structures still need further exploration.Taking Longnan mountain area in Gansu Province,which is prone to flash floods,as an example,this paper introduces the flash flood potential index(FFPI)to build an evaluation system and framework in flash flood risk assessment.Firstly,the spatial distribution of FFPI in the study area is constructed by selecting slope,land use,soil texture and fractional vegetation cover(FVC),combined with analytic hierarchy process(AHP)and information entropy.Secondly,the hazard and risk distribution of flash floods in the study area were obtained by introducing 0~24 h cumulative the maximum rainfall,rainy season average rainfall and flow accumulation as driving factors,and GDP and population density as hazard-bearing bodies.It is also verified with the historical flash flood data in this area.The results show that:the accuracy of using the FFPI model combined with AHP and information entropy to assess the risk of mountain flash floods in Longnan of Gansu Province is higher,and about 95.77%of the historical flash flood data are distributed in the medium,high and very high grades.From the perspective of administrative areas,the high and very high risk areas of flash floods in the study area are mainly distributed in Hanwang Town,Cheng County and Kang County of Wudu District,accounting for 31.5%,28.3%and 18.1%respectively.And the low risk areas are mainly located in some areas of Li County,Zhouqu County and Wen County,accounting for 18.9%,18.4%and 13.6%respectively.From the analysis of watershed scope,the high risk areas of flash floods in the study area are mainly concentrated in the downstream areas of rivers with gentle terrain,high population density and relatively developed economy,and the low risk areas are mainly located in the west and north of the study area with higher terrain.The research results are consistent with the field investigation of flash floods in the study area.The model constructed in this study and the credible assessment results can provide a reference and theoretical basis for flash floods prevention and hazard reduction and related research in Longnan mountain area of Gansu Province.