Debris Flow Risk Assessment And Adaptation Strategies Under Climate Change

Disaster risk management under climate change has drawn the attention from both domestic and international scholars.As a typical mountainous disaster,debris flow poses a threat to the sustainable development of human society in mountain area continuously.Climate Change may change the characteristics of regional disaster systems components,leading to a social-economic future with scarce natural resources,refined activity spaces,restrict workplace and other negative effects on basic human survival.In recent years,with the intensification of extreme climate events and the accelerated evolution of disaster environmental condition caused by climate change,disaster risk reduction and corresponding adaptation take precedence over all other considerations from researchers and governors in both disaster management and social development management.Considering the components of debris flow risk under climate change,it is important to understand both natural dimension and social dimension of risk,that is hazard and vulnerability respectively.As the critical preconditions of risk,the distribution and degree of debris flow hazard is beneficial for risk reduction.Extreme weather and climate events caused by climate change are important prerequisites to trigger future debris flows.In order to assess future debris flow hazard,the evaluation of spatial and temporal distribution and change trend of extreme precipitation events for the future are needed in the first place.Based on the observation data,three general circulation models from CMIP5 were statistically downscaled to analyze the spatial and temporal distribution of extreme precipitation in the study area for the period of 2010-2060.Second,the downscaled precipitation data were applied to the soil and water coupling model to simulate rainfall-triggering debris flow for hazard assessment.For model integration,the meteorological data were processed to the same condition of sampling spatial resolution of soil,elevation and geology data.In addition to debris flow hazard,the vulnerability of mountain settlements is not only the vital driving factor for forming the risk of debris flow under climate change,but also the essential source of adaptation.At present,researches on disaster vulnerability are carried out mostly from a single disaster-bearing body or a specific dimension,in other words,it is believed that vulnerability is caused by the physical resistance of buildings in areas with potential danger from debris flow,or the individual characteristics of population in disaster-prone areas.However,the long-term and comprehensive nature of regional social characteristics of climate change challenges this hypothesis.This study aims to establish a comprehensive vulnerability index involving demography,society,economy and other aspects to evaluate the debris flow risk of mountainous settlements under climate change.In addition,a multi-agent based model of human time-space behavior planning scheme is proposed to address the causes of the vulnerability of mountainous settlements in the upper reaches of the Minjiang river.The main work and conclusions of this study are as follows:(1)Three GCMs,BCC?CSM,CCSM4,and MIROC5,were chosen to project future spatial-temporal distribution and changing trend of extreme precipitation.13 extreme precipitation indices were established from intensity,frequency and event duration characterisitics for the upper reaches of the Minjiang river in the next 50 years.The results showed that most of the regional extreme precipitation in the study area may be enhanced.Areas with the largest extreme precipitation intensity is the Hei river basin with the heaviest rainfall and the Shouxi river basin with the longest duration heavy rainfall events.In addition,simulation results of three GCMs showed significant differences.BCC?CSM showed the greatest spatial variance in the pattern of extreme precipitation.CCSM4 showed greater intensity of extreme precipitation,while MIROC5 showed smaller extreme precipitation.(2)This study constructed a method for debris flow risk assessment under climate change.By combining large scale and long time series of climate change data with the debris flow mechanism projection model based on water-soil coupling dynamic.The frequency of debris flow in the future 50 years representing hazard in the upper reaches of the Minjiang river were obtained.The result showed that debris flow events were projected to occur in 80 ? 280 watersheds from the total number of 576 in the study area.Debris flow events with the highest frequency were located in Wenchuan and Maoxian counties with 2-year return period while others with 5-year or 10-year return period.In general,debris flow hazard showed significantly increasing trend in the study area.(3)Differs from previous study thought vulnerability based on monomer resistance,this paper laid a foundation that the economic and social development level shapes the vulnerability of mountainous settlements.Hence demographic,economic and social structure dimensions were included in the comprehensive index of mountain settlements vulnerability.The principal component analysis method was adopted to evaluate the vulnerability of the upper reaches of Minjiang river under climate change.Results showed that the local population and the backward transportation and other infrastructure system were the predominant factors that made the settlements vulnerable to disasters.The principal component load is 42% and 29%,respectively.Moreover,demographic characteristics increased the complexity of vulnerability.(4)Debris flow disaster risk under climate change is the result of hazard and vulnerability.The results of settlement risk grade and risk composition categories in the study area showed that the distribution of debris flow risk and hazard was significantly different,indicating that the improvement of settlements social and economic status had been an important instrument for debris flow risk reduction.Therefore,the countermeasures to improve the settlement adaptability in terms of strengthening disaster preparedness,improving livelihood,strengthening government management and preparing for uncertainty of climate change for different risk composition category can effectively serve for the management of disaster risk reduction.(5)Transportation system and complex terrain in mountainous areas may increase the space resistance of people to evacuate in a debris flow event.In order to further improve the settlement adaptability,the multi-agent model was applied to simulate evacuation behavior,to work out evacuation pathway,and to develop shelter locating plans in debris flow scenario.Taking Netlogo software as the analysis and visualization platform,methods based on MBM were able to provide the path selection scheme and potential safe havens for individual and household at different disaster phase,and to display the interaction between the spatial behavior of personnel and the traffic network.