Abstract
Debris flows, which cause massive economic losses and tragic losses of life every year, represent serious threats to settlements in mountainous areas. Most deaths caused by debris flows in China occur in buildings, and the death toll is strongly dependent on the time people spend indoors. However, the role of time spent indoors in the quantitative analysis of debris flow risk has been studied only scarcely. We chose Luomo village in Sichuan atop a debris flow alluvial fan to study the influence of the temporal variation in the presence of people inside buildings on the societal risk. Two types of days (holidays vs. workdays) and two diurnal periods (daytime vs. nighttime) were considered in our risk evaluation model. A questionnaire survey was conducted for each family in the village, and the probability of the temporal impact of a debris flow on every household was calculated based on the average amount of time each member spent in the house. The debris flow hazard was simulated with FLO-2D to obtain the debris flow intensity and run-out map with return periods of 2, 10, 50, and 100 years. The risk to buildings and societal risk to residents were calculated quantitatively based on the probabilities of debris flow occurrence, the probability of the spatial impact, and the vulnerabilities of buildings and people. The results indicated that societal risk on holidays is always higher than that on weekdays, and societal risk at night is also much higher than that in the daytime, suggesting that the risk to life on holidays and at night is an important consideration. The proposed method permits us to obtain estimates of the probable economic losses and societal risk to people by debris flows in rural settlements and provides a basis for decision-making in the planning of mitigation countermeasures.
Highlights
Debris flows are the most frequent and destructive hazards in mountainous regions
The two priorities in the assessment of debris flow risk in rural settlements are evaluating the risks posed to buildings and life; while the risk to buildings has been studied by many researchers, few studies have focused on the risk to life
Damage to buildings and loss of life are the two serious consequences induced by debris flows in rural settlements
Summary
Debris flows are the most frequent and destructive hazards in mountainous regions. In particular, China is affected by debris flows every year and suffers enormous casualties and losses of property, especially in rural settlements. Debris Flow Societal Risk resources of China, 2018), with approximately 855 events occurring every year The majority of these disasters occurred in rural settlements with poor disaster prevention and recovery capabilities (Chen et al, 2013; Li et al, 2016; Ding et al, 2018). The dynamics of the populace significantly affect the exposure of people to natural hazards and the corresponding risk to life (Chen et al, 2004; Aubrecht et al, 2012; Ara, 2014), because the locations and presence of people in rural settlements always vary with the time of day (Van Westen, 2004). The most common approach is to employ the statistical average number of work hours to reflect the temporal impact on risk to life (Bell and Glade, 2004; Corominas et al, 2005; Mousavi et al, 2011); this metric cannot indicate the presence of the population in different locations and at different times of day
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