Mountain Hazards

Twenty years ago, concerns arose about the perceived effects of upper basin deforestation (e.g., in Nepal) on catastrophic flood disasters in the Ganges River Basin downstream as far as Bangladesh, which are analogous to current concerns about Himalayan glaciers. A team of mountain scientists began to question these perceptions, and compiled a volume titled The Himalayan Dilemma: Reconciling Development and Conservation (Ives and Messerli, 1989). Research in The Himalayan Dilemma marshaled evidence that shed new light on processes of deforestation in the headwaters, refuted popular notions of mountain peoples’ responsibility for lower basin flooding, and refocused attention on mesoscale relationships among land use, land cover, flood hazards, and economic development in the mountains, foothills, and upper piedmont settlement regions. The snow and ice hazards of concern in this report differ from the issues of 20 years ago, for example, in their attribution of responsibility to global rather than mountain societies, but the focus on the mountains as a source of downstream hazards invites analogies with the types of rethinking that are needed. To what extent, and in what ways, do the unfolding mountain snow and ice risks in the HKH region relate to other natural hazards in the region? Five propositions may be considered:

• Mountain hazards can attenuate with distance downstream.

• Mountain hazards can cascade and amplify downstream (e.g., because of increased downstream vulnerability or “associated disasters” triggered by those upstream).

• Mountain hazards can concatenate with other hazards downstream. They can attenuate while also being amplified by independent disasters downstream (Butzer, 1982).

• Mountain hazards can be compounded by independent disasters in different subregions that divert relief efforts from one disaster to another.

• Mountain hazards can be eclipsed by other crises downstream.

These five scenarios defy simple generalizations across the region. They may occur in succession with or adjacent to one another. One way of approaching them is to examine the historical geographic record of natural disasters in South Asia. The following analysis gives a sense of the magnitude of mountain hazards relative to those of the plains and coasts. It complements other discussions in this report regarding historical and future linkages among the hazards of mountains, plains, and coasts—and it is supported by information from a variety of disaster databases that are discussed in further detail in Appendix D.

Natural Disasters in South Asia

Natural disasters in South Asia can involve meteorological, hydrological, and geophysical phenomena that are obviously not unique to the HKH region. In 2010, hydrological disasters were more common than other types of disasters in the region (Munich RE NatCatSERVICE).3 A similar pattern is observed over the past century, the frequency of natural disasters in the region being flood dominated when compared with other disasters (Figure 4.1), both in terms of the frequency of events and number of people affected by the occurrence of floods (Figure 4.2). However, the number of people killed over the past century by natural disasters was dominated by droughts and related famines; the number of people killed by floods in the 20th century is smaller (Figure 4.3).

It should be underscored that these national disaster data cover entire countries in the South Asian subcontinent over the past century, and not just the region affected by mountain hydroclimatology. This macroregional perspective over a century reflects the uncertainties of aggregate data analysis. For example, Several catastrophic drought and famine events occurred in South Asia during the first half of the 20th century. Thus, although the frequency of droughts and famines over the past century in the region is relatively low (Figure 4.1), Figure 4.2 and 4.3 reflect the major impacts of these events in terms of people affected and people killed.


3 The NatCatSERVICE database is a comprehensive natural catastrophe loss database. The statement in the text is based on statistics from this database on major global natural catastrophes in 2010. See

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