Despite global technological and economic development, a large proportion of the nearly 1.5 billion people living in severe poverty at the dawn of the new millennium are located in Asia. Global per capita water supplies are declining and are now 30% lower than they were 25 years ago. By 2050, as much as 42% of the world's population may have to live in countries with insufficient freshwater stocks to meet the combined needs of agriculture, industry, and domestic use. The world's population will reach at least 8.9 billion by the middle of the 21st century (United Nations, 1998). India and China alone now account for 38% of the world's population. Most of the additional population would be in developing countries. These countries are likely to suffer adverse agricultural responses; significant changes in seasonal runoff; possibly severe vector-borne diseases; increased risks of severe tropical weather disturbances, including storms; vulnerability to sea-level rise; and other stresses. This section presents key regional concerns of various subregions of Asia related to climate change.
Relatively hospitable mountain regions in Asia are under pressure from human settlements and commercial cultivation, which have led to land degradation and adverse effects on water supply. Ongoing changes in different mountain systems within Asia include those associated with high crop production and those characterized by extensive animal husbandry and pastureland. Human encroachment in mountain regions has reduced vegetation cover, which has increased soil moisture evaporation, erosion, and siltationwith adverse effects on water quality and other resources. Changes in the snowfall pattern have been observed in mountain and highland systems, particularly in the Himalayas (Verghese and Iyer, 1993). These changes will have wider implicationsfrom marked impact on the monsoon regime to seasonal runoff and vegetation cover, including agriculture. Changes in the hydrological regime also will trigger episodes of extreme events.
One-tenth of the world's known species of higher altitude plants and animals occur in the Himalayas. In addition, some countries in Asia are centers of origin for many crop and fruit-tree species; as such, they are important sources of genes for their wild relatives. Biodiversity is being lost in these regions because of human activities, especially land degradation and the overuse of resources. In 1995, approximately 10% of known species in the Himalayas were listed as threatened, and the number of species on the verge of extinction has increased since then. As a consequence of global warming, the present distribution of species in high-elevation ecosystems is projected to shift to higher elevations, although the rates of vegetation change are expected to be slow and colonization success would be constrained by increased erosion and overland flows in the highly dissected and steep terrains of the Himalayan mountain range. Weedy species with a wide ecological tolerance will have an advantage over others (Kitayama and Mueller-Dombois, 1995). High-elevation tree speciessuch as Abies, Acer, and Betulaprevail in cold climates because of their adaptations to chilling winters. In Japan, the area of suitable habitat at higher elevations has shrunk over the past 30 years, and the variety of alpine plants that grow there has been rapidly reduced (Masuzawa, 1997, 2000). Increases in temperature would result in competition between such species and new arrivals. The sensitivity of alpine flora to climatic factors and, in particular, water stress in the summit region of Mt. Kinabaluthe highest mountain in southeast Asiaalready have been demonstrated (Kitayama, 1996; Aiba and Kitayama, 1999). The accumulated stresses of climate change are likely to disrupt the ecology of mountain and highland systems.
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