The intense tectonic activities and complex geomorphology have made the Tibetan Plateau the highly potential area of mountain hazards, including glacial lake outburst, torrential floods, debris flows, landslides, and avalanches, especially caused by the coupling of avalanches, glacier movement, snow melting, and extreme precipitation (Fig. 1). Moreover, the disasters usually occur in chains and are amplified by cascaded processes, involving a variety of types of disasters in a long period and over a wide range of space. Therefore, it is significant to carry out quantitative study on the physical features, formation mechanism, dynamic process, transformation of disaster chain, and risk analysis of mega mountain hazards under climate change, and eventually to propose reasonable disaster mitigation measures to reduce risks from global climate change.
CURRENT RESEARCHES
The last 50 years have witnessed frequently extreme climate events (i.e. extremely high temperatures and rainstorm) in the Tibetan Plateau, which greatly increase the potentiality of various mountain hazards [1,2]. In particular, the glacial lake outbursts and the associated debris flows have become more active, and large-scale hazards in chains are more frequent [3].
Researches on the Tibetan Plateau are concerned on the safety of main highways and railways, hydropower, and water conservancy projects or urban disaster mitigation. Significant progress has been made on disaster prevention and control technology. For example, benefiting from the road reconstruction and disaster mitigation countermeasures, the annual interrupted traffic time of the National Highway G318 from Sichuan to Tibet has been shortened from more than 3 months to several days at present. Typical disaster cases in the plateau aroused widespread concerns in the academic community. A systematic study has been ongoing for the Yigong landslide and the related chain of processes that occurred on 9 April 2000 [4]. Disaster risk assessments on regional scale or individual events have been well developed. On the regional scale, the assessment is made on base of the formation factors and conditions by comparing remote sensing images [5]; and for individual disasters, numerical simulations are usually used for assessment [6]. Disaster chain is especially significant in some events, such as the outburst of glacier lakes, which involves dam break, outburst flood, and debris flow. Eighteen events in the past 70 years have been systematically explored to reveal their formation, evolution, and mitigation [7]. Recently, following the release of IPCC Fifth report, concerns for the effects of climate changes on disaster and adapted countermeasures are growing, and preliminary progress has been made in finding relations of various disasters with the extreme climate weather [3,8].
There are still deficiencies in the present studies. To list some of the major ones, we consider the following:
Prediction: Observations and data about mountain hazards are extremely scarce in the study area, and the available data, such as the weather data obtained from the spots far away from the hazard points, cannot exactly reflect the real formation conditions of hazards at high altitude; and calculation from regional remote sensing data needs further validation. Data limitation has been a long stumbling block for quantitative forecasting model.
Dynamics: There is a lack of researches on dynamics of hazard formation and mass movement in extremely cold areas. Existing analysis and simulations of landslides help little for the study of the dynamic characteristics, failure criteria, and the movement of glacial till, due to insufficient understanding of basic physical properties of wide-graded moraine soil.
Risk analysis: Attention should be paid to multi-process of hazard chain and multi-scale risk. The definition of vulnerability was announced by the United Nations in 1992 [9], and vulnerability analysis research as developed from an earlier qualitative evaluation by expertise method to a quantitative evaluation. Field experiments simulate the physical processes of structure destruction well [10] but fail to satisfy the similarity rules; on the other hand, lab experiments apply to dynamical investigation but the results are usually of little practical application [11]. Therefore, the key to intensify risk analysis is to determine the dynamic mechanism of interaction between different disasters and bearing bodies.
The distribution of mountain hazards in Tibetan Plateau. (a) Overall distribution in entire region. The present inventory includes more than 2000 debris flows, 1500 landslides, and 1100 natural dams which concentrated in Himalayas and eastern mountains of Tibetan Plateau. (b) Distribution in Palongzangbu basin.
The distribution of mountain hazards in Tibetan Plateau. (a) Overall distribution in entire region. The present inventory includes more than 2000 debris flows, 1500 landslides, and 1100 natural dams which concentrated in Himalayas and eastern mountains of Tibetan Plateau. (b) Distribution in Palongzangbu basin.
RISK GROWTH
It is estimated that temperature will get a rise of 3.2°C–3.5°C by 2050 and 3.9°C–6.9°C by 2100 compared with the reference period (1961–1990), accompanied by rainfall rise of 10.4%–11.0% and 14.2%–21.4% [12]. Rise in temperature and rainfall will increase the risk of glacial lake outburst and the ensuing flash floods, debris flows, and landslides. Frequency and scale of mountain hazards are supposed to get higher in the future, which increases the risk of disasters. Intensive human activities are concentrated in the valley areas for relative rich hydrothermal resource and flat terrain. The valleys with increasing density of population and economy are coincident with the risk areas of mountain hazards, which make the situation of vulnerability and risk worse [3].
ISSUES OF FUTURE CONCERN
The quantitative relationship between forming factors of mountain hazards and climate change, and disaster prediction.
The hazard formation conditions (glacial lake, vegetation, moraine deposit, terrain) and triggering criteria (rainfall, ice and snow melting, ice avalanche) vary from climate change and affect the future development of mountain hazards. Prediction model should be established to overcome the difficulty of data limitation. Using different spatial and temporal monitoring techniques and selecting high-sensitive and high-resolution remote sensing data (on water, glacier, vegetation, heat, etc.) to set up an efficient methodology of data acquisition could solve this issue.
Dynamics of mountain hazard chain.
The probability of large-scale disasters and ensuing hazard chain increases in the Tibetan Plateau, especially at plateau edge areas, but no dynamical model is available for incorporating the chain processes of landslides, debris flows, flash floods, avalanches, and glacial lake outbursts. Therefore, insufficient understanding of the formation mechanism of mountain hazards and assessment of disaster risk actually restrict engineering planning and design.
Multi-scale quantitative risk assessment.
To develop quantitative assessment methods and risk prediction for multi-scale mountain hazards in plateaus at different levels of watershed, main towns and major projects, is the key to assess disaster risk under different circumstances, such as climate change and strong earthquakes in the future, and to propose the targeted mitigation countermeasures. This requires establishment of methods as well as determination of indicators for risk evaluation and vulnerability assessment at different scales. Particularly, for risk assessment on main towns and major projects, it is necessary to work out numerical simulation of the chain processes and finally to build risk assessment model.
This research was supported by the key project (41190084) and the key international collaborative project (41520104002) of the Natural Science Foundation of China.
REFERENCES
