Comparative Study on the Land-cover Change and Global Warming Impacts on Regional Climate in Northeast Asia

Mongolia is situated in an arid/semi-arid zone in Northeast Asia. The southern part of the territory has a desert type climate. The thermal effect of the Tibetan Plateau is the principle reason for the desert climate, remotely suppressing convective systems in the arid region (Sato and Kimura, 2005a). On the other hand, Taiga forest covers the northern part of Mongolia, extending to Siberia in Russia. More than half of the annual precipitation is observed during the summer season in Mongolia (Batima and Dagvadorj, 2000). The territory has a prominent meridional contrast in its rainfall amount as well as in its surface conditions that changes drastically from desert to grassland and to forest over a range of only several hundreds of kilometers from south to north. In general, such transition zones are very vulnerable to the climate change; as are the economic activities in this region. Annual precipitation in Northeast Asian arid region is only several ten millimeter to few hundred millimeter per year. Most part of the annual precipitation, which has the large interannual variation, falls in the warm season. Thus, this study mainly focuses on the June-July-August period. Yatagai and Yasunari (1994) showed a significant increasing trend in wintertime air temperature from 1951 through 1990. On the other hand, the summertime temperature change does not show increase/decrease trend in the same period. Precipitation trend during 1960-1998 shows that both increasing and decreasing trends coexist in Mongolia (Endo et al., 2006). Figure 1 shows interannual variation of daily mean, daily maximum, and daily minimum temperature in July at eight stations in Mongolia. As shown by Yatagai and Yasunari (1994), longer-term trend is very small in summer before around 1990. However, after 1990, significant increase in daily minimum temperature is observed even in summer. In Mongolia, after the change of political system, the number of livestock had increased (Sugita et al., 2006), which may accelerate the land surface degradation. As examined by Eastman et al. (2001), intense grazing may have the potential to alter the local climate. In order to know how regional temperature and precipitation can be affected by the two factors, global warming and land cover change, sensitivity experiments were carried out using the regional climate model (RCM).