| It has become focal research topics worldwide to make researches on both the formation mechanism of disasters in landslide and debris flow prone areas, and sustainable development strategies based on prevention and mitigation of disasters. The vulnerable natural environmental conditions and human's negative impacts in central and southern Gansu Province, China resulted in ecological degradation, active and frequent landslides and debris flow, and continuous poverty.A regional evaluation system was set up based on analysis of study region's environmental factors, land system and landslide mechanism at deferent time scales, and raster cells as our basic study unit to evaluate the magnitude of landslide debris hazards were identified by using Geographic Information Systems (GIS), MATLAB and fuzzy methods in the paper. In addition, a system of indicators of impact of regional landslide and debris flow on regional sustainable development was developed, which can be used for impact assessment of landslides and debris flow on sustainable development based on county levels. The potential hazard areas and types can be clarified according to the assessing results and analysis of related factors. Therefore, key strategic points and regional strategic measures for sustainable development as well as scientific consulting and decision-making will be worked out in accordance with prevention and mitigation of landslides and debris flow by taking into account of economic development priorities, ecological conditions and impact of landslides and debris flow on sustainable development. Main conclusions drawn from the research are as follows:1. The formation mechanism and process of landslide and debris flowThe study region is characterized with being one of the most sensitive and fragile land systems as well as one of most frequent and prone areas of landslide and debris flow in China. The fragile land system is the root cause for high frequency and magnitude of landslides and debris flows in this region. In early Quaternary Period, the frequency and magnitude of this kind of natural hazards were even much worse than what they are today. However, the past 50 years had become a peak period when more improper intensive human activities intensified the frequency of such hazards greatly. The trigger-response mechanism is the core mechanism for controlling the spatial scale and magnitude of landslide and debris flows. Therefore, it is very important to know the trigger-response threshold in the region where hazard risk is higher in order to develop a better hazard forecasting system and to know the distribution pattern of the landslides and debris flows.2. Strength assessment of landslide and debris flowsBy using GIS, MATLAB and FUZZY method, the strength of landslides and debris flows could be evaluated based on high resolution images. Four kinds of strength scales were divided in the research area:â… . Area with high frequency, high response and high strength (western Longnan area);â…¡. Area with high frequency, low response and low magnitude (eastern Longnan area);â…¢. Area with low frequency, high response and low magnitude (central and southern region in central Longzhong);â…£. Area with low frequency, low response and low magnitude (northern of central Longnan area).3. Impacts of landslides and debris flows on sustainable development in the study region In this study region, hazards of landslides and debris flows have intensified the conflicts between humanity and land system. As a result, economic development has consumed natural resources greatly and caused more serious environmental degradation. Thus, in this region, these two factors have integrated together and created both Domino Effect and PPE Circle (The vicious circle among the increase of population, poverty and environmental degradation). As a result, hazard prevention strategy in a sustainable way is much more effective than simple hazard prevention methods.4. Assessment of impacts of landslide debris flows on sustainable developmentCounties located in western Longnan, eastern Gannan Plateau and Tianshui have the highest risk of landslide and debris flows. Counties in eastern Longnan and central and southern Longzhong have the highest potential risk possibilities. Lanzhou, Wudu and Tianshui have formed three areas prone to hazards. Xihe, Lixian, Dangchang, Wenxian, Zhouqu and Chengxian that surround Wudu area have higher risk possibilities as well. Along the Wei River, six counties that are distributed around Tianshui, including Wushang, Gangu, Qin'an, Zhuanglang, Longxi and Zhangxian, are areas having higher hazard risk as well. Those areas having the lowest hazard mitigation capacities include the state-designated poverty and minority counties including Zhuoni, Diebu, Zhouqu, Jishishan, Dongxiang, Hezhen, and Linxia as well as some remote disadvantaged poverty countries such as Diexian, Kangxian, Wenxian, Liangdang, and Mingxian. Wudu, Wenxian, Zhouqu, Dangchang, Tianshui, Lixian and Lanzhou are areas where hazards have formed most strength impact on sustainable development, and Xihe, Wushan, Diebu, Mingxian, Gangu, Zhangxian, Qingan and Kangxian have potential strength impact on sustainable development.5. Regional hazard types classification The area can be divided into 10 types of hazards according 10 the hazard risk possibilities of landslides and debris flows:Lower risk--less hazard region in Northern Loess Plateau, higher risk-higher to medium hazard region in central and northern Loess Plateau, higher to lower risk--moderate hazard region in central and southern loess plateau; the high, higher to medium risk-medium to high hazard region in the southeastern parts of Longzhong Loess Plateau; High risk-high and higher hazard region in western parts of Longnan hills; high and higher risk-higher hazard region in northern parts of Longnan hills; higher to medium risk-higher hazard region in eastern parts of Longnan hills; low risk hazard region in southwestern Loess Plateau; high, higher and moderate risk--moderate to high hazard region in the western mountain region; higher risk-higher and medium hazard region in the transition zone of Longzhong, Longnan and Gannan Plateau; and higher risk-lower hazard region in the eastern parts of Ganan plateau.6.Sustainable hazard prevention strategiesKey strategies consist of following points:6.1 To speed up economy development and adjust development approaches;6.2 To develop principles of prevention of landslide and debris flows;6.3 To develop an effective model for prevention of and control for landslides and debris flow through ecological rehabilitation;6.4 To control major landslides and debris flows in phases by expanding channels for disaster funds, by abiding by the cost-benefit principle;6.5 To focus on prevention-oriented strategies and utilize land resources in a more intensification way;6.6 To control population, migration and urbanization;6.7 To increase population quality by improving information technology and education;6.8 To strengthen the hazard management measures;6.9 To strengthen research on the disaster monitoring, early-forecasting and warning technologies in order to improve hazard prevention ability.
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