Susceptibility evaluation for debris flow in different watershed units considering freeze-thaw erosion type sources:taking Gonjo area of eastern Tibet as an example
Debris flows pose a significant geological hazard,inflicting severe damage to infrastructure such as buildings and roads in eastern region of the Qinghai-Tibet(Xizang)Plateau.Considering the background of global warming,the likelihood of potential debris flow occurrences in the mountainous areas of the Qinghai-Tibet Plateau is expected to rise.Therefore,a quantitative assessment of debris flow susceptibility assumes great importance as the primary approach for implementing regional disaster reduction and prevention measures.The formation of debris flows is influenced by source conditions,terrain conditions,and water conditions.In this study,we focus on the variability of source and terrain conditions while temporarily assuming constant water conditions within a small area.Specifically,we address the challenge of determining and quantifying source con-ditions by examining the freeze-thaw erosion type provenance in the Gonjo(Gongjue)area of eastern Tibet.Through detailed field investigations and comprehensive research,we calculate the freeze-thaw erosion intensity(DR)to represent the source conditions of debris flows.To evaluate debris flow susceptibility,we select eight factors related to source and terrain conditions,including freeze-thaw erosion intensity(DR),elevation(H),plane curvature(Pl_cv),profile curvature(Pr_cv),slope(Slope),stream power index(SPI),topographic wetness index(TWI),and terrain characterization index(TCI).The weight values of these eight evaluation fac-tors are determined using the analytic hierarchy process(AHP)and principal component analysis(PCA)meth-ods.The susceptibility of debris flow in Gonjo area of eastern Tibet is then evaluated using the weighted informa-tion method.Additionally,the study divides the watershed units into four groups based on different flow thresh-olds(5 000,10 000,20 000,and 40 000)and analyzes and compares the susceptibility evaluation results of each group.The evaluation results are further validated using the receiver operating characteristic curve(ROC)analysis.The main findings of this study are as follows:Firstly,among the selected evaluation factors,freeze-thaw erosion intensity(DR),terrain characterization index(TCI),and plane curvature(Pl_cv)exhibit the high-est weight values,with their cumulative weights exceeding 0.5.This indicates that these three factors are more sensitive to debris flow formation in the study area and contribute significantly to debris flow susceptibility.Sec-ondly,based on the susceptibility evaluation results of the four groups of watershed units,the group G2(flow threshold 5 000)demonstrates the highest area under the curve(AUC)value,followed by groups G3 and G4,while group G1 exhibits the lowest AUC value.These results highlight the efficacy of employing the G2 group to divide watershed units when conducting debris flow evaluations in the study area and surrounding regions,as it yields relatively accurate evaluation outcomes.Lastly,the study establishes a debris flow susceptibility evalua-tion model incorporating freeze-thaw erosion type provenance and topographic hydrological factors,which yields satisfactory evaluation results.This indicates the viability of integrating freeze-thaw erosion intensity to characterize source factors and underscores the feasibility of a susceptibility evaluation system primarily driven by provenance and topography in Gonjo area of eastern Tibet.In conclusion,this study introduces novel method-ologies and concepts for assessing debris flow susceptibility in the region,where freeze-thaw erosion phenomena are prevalent.The findings significantly contribute to the theoretical research and hold practical implications for guiding local authorities in disaster prevention and mitigation efforts.
susceptibility evaluation for debris flowfreeze-thaw erosion intensitytopographic hydrological factorsweighted information methodGonjo area of eastern Tibet
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