11.4.3.2 Precipitation and Associated Circulation Systems

The MMD models indicate an increase in annual precipitation in most of Asia during this century, the percentage increase being largest and most consistent among models in North and East Asia (Figure 11.9 and Table 11.1). The main exception is central Asia, particularly its western parts, where most models simulate reduced precipitation in the summer. Based on these simulations, sub-continental boreal winter precipitation is very likely to increase in northern Asia and the Tibetan Plateau, and likely to increase in eastern Asia. It is also likely to increase in the southern parts of Southeast Asia. Summer precipitation is likely to increase in North, South, Southeast and East Asia, but decrease in central Asia. Probability estimates from Tebaldi et al. (2004a; see Supplementary Material Table S11.2) support these judgments.

The projected decrease in mean precipitation in central Asia is accompanied by an increase in the frequency of very dry spring, summer and autumn seasons; conversely, in winter, where models project increases in the mean precipitation, very high precipitation becomes more common (Table 11.1). The projections of changes in mean precipitation and, where available, precipitation extremes, are discussed in more detail below for individual Asian regions. Where appropriate, the connection to changes in circulation systems that bring precipitation is also discussed. Smaller (slightly larger) changes are generally projected for the B1 (A2) scenario, but the inter-scenario differences are small compared with the inter-model differences.