10.2.1 Asia: regional characteristics
Asia is the most populous continent (Figure 10.1). Its total population in 2002 was reported to be about 3,902 million, of which almost 61% is rural and 38.5% lives within 100 km of the coast (Table 10.1). The coastline of Asia is 283,188 km long (Duedall and Maul, 2005). In this report, Asia is divided into seven sub-regions, namely North Asia, Central Asia, West Asia, Tibetan Plateau, East Asia, South Asia and South-East Asia (for further details on boundaries of these sub-regions see Table 10.5).
North Asia, located in the Boreal climatic zone, is the coldest region of the northern hemisphere in winter (ACIA, 2005). One of the world's largest and oldest lakes, Baikal, located in this region contains as much as 23,000 km3 of freshwater and holds nearly 20% of the world surface freshwater resources (Izrael and Anokhin, 2000). Central and West Asia include several countries of predominantly arid and semi-arid region. Tibetan Plateau can be divided into the eastern part (forest region), the northern part (open grassland), and the southern and central part (agricultural region). East Asia stretches in the east-west direction to about 5,000 km and in the north-south to about 3,000 km including part of China, Japan and Korea. South Asia is physiographically diverse and ecologically rich in natural and crop-related biodiversity. The region has five of the 20 megacities of the world (UN-HABITAT, 2004). South-East Asia is characterised by tropical rainforest, monsoon climates with high and constant rainfall, heavily-leached soils, and diverse ethnic groups. Table 10.1 lists the key socio-economic and natural resource features of the countries of Asia (WRI, 2003; FAO, 2004a, b, c; World Bank, 2005).
10.2.2 Observed climate trends, variability and extreme events
Past and present climate trends and variability in Asia are generally characterised by increasing surface air temperature which is more pronounced during winter than in summer. Increasing trends have been observed across the seven sub-regions of Asia. The observed increases in some parts of Asia during recent decades ranged between less than 1°C to 3°C per century. Increases in surface temperature are most pronounced in North Asia (Savelieva et al., 2000; Izrael et al., 2002a; Climate Change in Russia, 2003; Gruza and Rankova, 2004).
Interseasonal, interannual and spatial variability in rainfall trend has been observed during the past few decades all across Asia. Decreasing trends in annual mean rainfall are observed in Russia, North-East and North China, coastal belts and arid plains of Pakistan, parts of North-East India, Indonesia, Philippines and some areas in Japan. Annual mean rainfall exhibits increasing trends in Western China, Changjiang Valley and the South-Eastern coast of China, Arabian Peninsula, Bangladesh and along the western coasts of the Philippines. Table 10.2 lists more details on observed characteristics in surface air temperature and rainfall in Asian sub-regions.
10.2.3 Observed changes in extreme climatic events
New evidences on recent trends, particularly on the increasing tendency in the intensity and frequency of extreme weather events in Asia over the last century and into the 21st century, are briefly discussed below and summarised in Table 10.3. In South-East Asia, extreme weather events associated with El-Nino were reported to be more frequent and intense in the past 20 years (Trenberth and Hoar, 1997; Aldhous, 2004).
Significantly longer heatwave duration has been observed in many countries of Asia, as indicated by pronounced warming trends and several cases of severe heatwaves (De and Mukhopadhyay, 1998; Kawahara and Yamazaki, 1999; Zhai et al., 1999; Lal, 2003; Zhai and Pan, 2003; Ryoo et al., 2004; Batima et al., 2005a; Cruz et al., 2006; Tran et al., 2005).
Generally, the frequency of occurrence of more intense rainfall events in many parts of Asia has increased, causing severe floods, landslides, and debris and mud flows, while the number of rainy days and total annual amount of precipitation has decreased (Zhai et al., 1999; Khan et al., 2000; Shrestha et al., 2000; Izrael and Anokhin, 2001; Mirza, 2002; Kajiwara et al., 2003; Lal, 2003; Min et al., 2003; Ruosteenoja et al., 2003; Zhai and Pan, 2003; Gruza and Rankova, 2004; Zhai, 2004). However, there are reports that the frequency of extreme rainfall in some countries has exhibited a decreasing tendency (Manton et al., 2001; Kanai et al., 2004).
Increasing frequency and intensity of droughts in many parts of Asia are attributed largely to a rise in temperature, particularly during the summer and normally drier months, and during ENSO events (Webster et al., 1998; Duong, 2000; PAGASA, 2001; Lal, 2002, 2003; Batima, 2003; Gruza and Rankova, 2004; Natsagdorj et al., 2005).
Recent studies indicate that the frequency and intensity of tropical cyclones originating in the Pacific have increased over the last few decades (Fan and Li, 2005). In contrast, cyclones originating from the Bay of Bengal and Arabian Sea have been noted to decrease since 1970 but the intensity has increased (Lal, 2001). In both cases, the damage caused by intense cyclones has risen significantly in the affected countries, particularly India, China, Philippines, Japan, Vietnam and Cambodia, Iran and Tibetan Plateau (PAGASA, 2001; ABI, 2005; GCOS, 2005a, b).
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