Geoscience Reference
In-Depth Information
9.3 Modeling the Asian monsoon climate
The Asian monsoon (AM) encompasses the vast region spanning the Indian
subcontinent, Southeast Asia and East Asia, surrounded by the Indian Ocean
and the western Pacific Ocean. It is home to more than half of the world's
population. The socioeconomic infrastructure of the mostly agrarian societies
in the AM region has been built, in large part, on the basis of a highly
reproducible annual cycle of rainfall. Agriculture, drinking water, health,
energy generation, and more generally the livelihood and well-being of this
vast human population all depend on monsoon rains. Imbedded in the large-
scale monsoon circulation are powerful rain-producing weather systems,
known as monsoon depressions. An anomaly of the AM in the form of a
slight shifting of the monsoon rain system will cause major flooding in one
place and drought in another. Droughts and floods are the major causes of
extensive destruction of the ecosystem, property damage, collapse of regional
economies, and loss of human life in the AM region.
While drought can cause crippling long-term effects on a country or a
region, a single season of flooding can be devastating. For example, the
widespread monsoon flood over central and eastern Asia during the summer
of 1998 was responsible for the loss of over 3000 human lives, damaged more
than 30 million acres (12 Mha) of farmland, and ruined over 11 million acres
(4.5 Mha) of crops. In all, the flooding inflicted an economic loss totaling
over 12 billion US dollars to China, and brought the country's economy to its
knees. Since much of the world's productivity relies on the natural, economic
and human resources residing within the thriving economies of the AM
region, our ability to predict the interannual changes in monsoon circulation
and rainfall is a critical requirement for the sustainable development not only
of the AM region, but of the world.
Understanding, modeling, and predicting monsoons is also of great impor-
tance to the projections of future climate change due to the increase in the
concentration of the greenhouse gases. The AM region is one of the few
places in the world for which nearly all climate models predict increased
rainfall in association with global warming. Furthermore, it has been
observed that the SST warming trend during the past 20 years has been
largest in the tropical oceans, especially in the Indian Ocean. Increased
convection in the Indo-Pacific region associated with the warming of the
Indian Ocean may be linked to long-term climate change in the North Atlantic
(Hoerling et al.
2001a
,
b
). Therefore an understanding of the possible effects
of a warmer Indian Ocean on the AM is essential to understand the regional
and global effects that may stem from global warming.
There is a large body of observational and modeling research that suggest
strong interaction between the ENSO and the AM. The ENSO and AM cycles
mutually affect each other. While neither ENSO nor the monsoon owe their
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