10.2.4.4 Natural ecosystems
Increasing intensity and spread of forest fires in Asia were observed in the past 20 years, largely attributed to the rise in temperature and decline in precipitation in combination with increasing intensity of land uses (Page et al., 2002; De Grandi et al., 2003; Goldammer et al., 2003; FFARF, 2004; Isaev et al., 2004; Murdiyarso et al., 2004; Shoigu, 2004; Vorobyov, 2004; Achard et al., 2005; Murdiyarso and Adiningsih, 2006). During the last decade, 12,000 to 38,000 wild fires annually hit the boreal forests in North Asia affecting some 0.3 to 3 million hectares (Dumnov et al., 2005; Malevski-Malevich et al., 2005; FNCRF, 2006). Recent studies have also shown a dramatic increase of fires in Siberian peatlands (of which 20 million ha were burnt in 2003) linked to increased human activities combined with changing climate conditions, particularly the increase in temperature. Fires in peatlands of Indonesia during the 1997 to 98 El Niño dry season affected over 2 million ha and emitted an estimated 0.81 to 2.57 PgC to the atmosphere (Page et al., 2002). In the past 10 years about 3 million ha of peatland in South-East Asia have been burnt, releasing between 3 to 5 PgC, and drainage of peat has affected an additional 6 million ha and released a further 1 to 2 PgC. As a consequence of a 17% decline in spring precipitation and a rise in surface temperature by 1.5°C during the last 60 years, the frequency and aerial extent of the forest and steppe fires in Mongolia have significantly increased over a period of 50 years (Erdnethuya, 2003). The 1997/98 ENSO event in Indonesia triggered forest and brush fires in 9.7 million hectares, with serious domestic and trans-boundary pollution consequences. Thousands of hectares of second growth and logged-over forests were also burned in the Philippines during the 1997/98 ENSO events (Glantz, 2001; PAGASA, 2001).
With the gradual reduction in rainfall during the growing season for grass, aridity in Central and West Asia has increased in recent years, reducing growth of grasslands and increasing bareness of the ground surface (Bou-Zeid and El-Fadel, 2002). Increasing bareness has led to increased reflection of solar radiation, such that more soil moisture is evaporated and the ground has become increasingly drier in a feedback process, thus adding to the acceleration of grassland degradation (Zhang et al., 2003).
Wetlands in Asia are being increasingly threatened by warmer climate in recent decades. The precipitation decline and droughts in most delta regions of Pakistan, Bangladesh, India and China have resulted in the drying up of wetlands and severe degradation of ecosystems. The recurrent droughts from 1999 to 2001, as well as the building of an upriver reservoir and improper use of groundwater, have led to drying up of the Momoge Wetland located in the Songnen Plain (Pan et al., 2003).