The Regional Impacts of Climate Change

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11.1.2. Physiography and Biogeography

Tropical Asia includes the major land masses of south and southeast Asia, as well as the long peninsulas that reach into the eastern Indian and western Pacific Oceans and the archipelagoes comprising the thousands of islands of Indonesia, Malaysia, India, and the Philippines (Figure 11-1). Physiographically, Tropical Asia is extremely complex and diverse. It contains the highest mountains on Earth, the deepest seas, and the largest number of islands-the latter making up what has been called the "maritime continent." The high mountains and the complex land-sea configuration have a strong influence on the weather and climate of the region.

Figure 11-1: Location and countries covered in the Tropical Asia region.

Geologically, Tropical Asia straddles the boundary between the Indo-Australian and Pacific tectonic plates. The collision and subduction zones between these plates are characterized primarily by earthquakes, land movements, active volcanism, and volcanic eruptions, which are major environmental hazards. Earthquakes and land movements also are responsible for local differences in relative sea level. The massive eruptions of Krakatoa in Indonesia more than a century ago and of Mount Pinatubo in the Philippines in 1991 caused climatic cooling extending far beyond the region (Parker et al., 1996).

Tropical Asia includes some large drainage basins, the sources of which extend into arid Asia to the north and west of the region. These basins include the Ganges, Brahmaputra, Meghna, Irrawaddy, and Salween Rivers, which drain into the Bay of Bengal and Andaman Sea; and the Nan, Mekong, and Red Rivers, which drain into the South China Sea. Varying impacts of climate change can be expected on the headwaters, broad valleys, and deltaic mouths of these catchments.

Biogeographically, the region includes the tropical Indo-Pacific borderlands, which have some of the greatest natural species diversity and productivity on Earth; coral reefs in the marine environment and tropical rainforests on land are prime examples. Ecological richness also is demonstrated by the region's crop and livestock diversity and by its large numbers of cultivars and varieties. The diversity of managed plants and animals is a result, in part, of climate and soil; it also reflects the length of human settlement in Tropical Asia, as well as its cultural and ethnic diversity. In addition, a number of animals, insects, and microbes have developed in parallel with the vegetation in this region.

Agriculture in Tropical Asia evolved on the basis of unique crop-related diversity, and only a few crops from other regions have become acceptable. Throughout the region, agriculture is critically important; it accounts for more than 30% of the gross domestic product (GDP) in at least seven countries. Climate-sensitive crops-such as rice, other grains and cereals, vegetables, and spices-are particularly important in the region. There is little doubt that agricultural systems in Tropical Asia have adapted to a range of environmental stresses over the region's long history of human settlement and land-use change. Whether such resilience can continue in the face of climate change and economic and population changes is uncertain, although it is expected that the processes of ongoing adaptation to changing environmental circumstances will continue.

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