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BY GEORGE: What really is a monsoon?

Most of us think of the “monsoon” season as the beginning of warm and wet weather from the previous season’s hot and dry period.  That is, the transition occurs in areas that have such climate regimes to begin with, primarily in Southeast Asia.  The problem is that it’s not that cut and dry of a definition, nor is it a cut and dry concept insofar as history is concerned. The monsoon definition is a highly disputed issue and still today the community of monsoon researchers has yet to find an accord.

Most people tend to simply relate the monsoon to the amount of rainfall that falls over a given region, i.e., from drought or near drought to heavy and sometimes excessive flood producing rainfall amounts. Some people use wind direction alone, or in combination with rainfall, while others might say it is the varying outgoing long-wave radiation, which can measure the height of clouds, temperature, or humidity.

Millions of people in Southeast Asia rely on the monsoonal rains for their livelihoods and food supply. The timing, onset, and length of the dry vs. wet periods are of prominent importance to millions of people in these regions.  It can literally spell feast or famine for untold millions.

In fact, the scientific research community hasn’t even agreed on what constitutes the actual beginning of a wet period, let alone if the wind regime should be taken into account as the seasons change.

There is a wide variation in what a monsoon season looks like, such  that the exact characteristics have still not been agreed on in the meteorological community as well.

There are all kinds of “official” definitions on what a monsoon or “monsoon season” is, all based on a variety of datasets, climate history, and calendar relationships to changing weather patterns in monsoon regions.

The main problem stems from that most definitions base the monsoon season on rainfall patterns, when the fact is, through history, the accepted and widely publicized definition surrounds a wind change, and not necessarily one related to rainfall.

In fact, the wind change season can occur independent of rainfall, and rainfall patterns might not coincide with a significant and long-lasting wind change pattern at all in some years.

As von Humboldt states in 1848, ‘Monsun’ (Malayan ‘musim’, the ‘hippalos’ of the Greeks) is derived from the Arabic word ‘mausim.’ The word has been applied to the seasons at which certain winds prevail, which are named from places lying in the direction from whence they come; thus, for instance, there is the ‘mausim’ of Aden, of Guzerat, Malabar, etc.

If the wind pattern and rainfall pattern did occur at the same time at the same place year after year, the confusion in truly defining a monsoon would not be as big an issue, nor as confusing as it is today.  For example,  In Bangladesh, the rain increases dramatically in April and May, up to 2 months before the large-scale monsoon circulation begins in earnest.

Just as various societies define the seasons of the year by various parameters, the number of those seasonal definitions are generally confined to winter, spring, summer, and fall, and do not vary to a great extent among most western and developed countries.  Furthermore, most people in each country generally accept the large four-season categories.  However, when it comes to regions with monsoon climates, history would suggest it is mainly a wind change definition, but over the years, rainfall seems to have trumped the true definition.  The ramifications of this type of confusion can be much more profound than defining winter beginning on December 21st or December 1st for example.  When it comes to monsoons, it’s often a matter of life and death.


By: George Elliott


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