An Indian woman carries her child to higher ground near Madanabori in the northeast state of Assam. (Anupam Nath/Associated Press)

In terms of total precipitation and lives affected, the annual monsoons that drench South Asia every summer are the grande dames of seasonal phenomena. Adding to that, this year's downpours seem to be packing an extra wallop.

Authorities throughout India, Pakistan, Bangladesh and Nepal are reporting one of the worst rainy seasons on record with some 28 million people displaced by flooding and a death toll of nearly 1,900 since late June when the rains began.

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Monsoon misery

That's shy, at this point at least, of the more than 2,200 killed during the 2004 summer monsoons in these four countries. Or the 1988 rains that flooded an estimated 75 per cent of Bangladesh and required a huge international relief effort to help alleviate the suffering. Still, this year's rains should be seen in a special context.

According to Indian meteorologists, who study these downpours with almost obsessive diligence, India recorded its highest-ever rainfall in a single day in late July when 94.4 centimetres (37 inches) fell on Mumbai, essentially shutting the country's main financial centre. Prior to that, the rainfall record was 83.8 centimetres and dated back to 1910 in the Indian state of Meghalaya, one of the rainiest locales on Earth,

An aerial view of a drowned village in the Indian state of Bihar. (Prashant Ravi/Associated Press) )

Indian authorities have been loathe to link this year's heavy rains directly to global warming — monsoons have been cycling through South Asia for something like 50 million years, most geologists say. But they may well end up being part of a year of record-breaking weather events.

As the World Meteorological Organization reported in August 2007 in Geneva, this year has been a year of extremes ranging from the rain-induced flooding in South Asia and Britain (in May and June) to heat waves in Eastern Europe and Russia and record snowfall in South Africa and parts of South America.

The first four months of the year were likely the warmest on record for the planet, a full one degree Celsius higher than average for the January to April period, the WMO said. And this summer is shaping up to be the hottest, as well, breaking the record set in 1998.

Ocean breezes on steroids

Seen in this context, monsoons would certainly appear to have some relationship with planetary warming because they are essentially sea breezes on steroids, dropping their moist ocean air over a super-heated land mass.

The term monsoon is said to originate from an old Arab word for season and refers to any regular seasonal change in the prevailing winds that result from the large temperature differences between land and the adjacent sea.

There are at least five major monsoon systems in the world: a North American one that brings moist air into the southern U.S. and Mexico from the Gulf of Mexico, and others that affect Brazil, sub-Saharan Africa, Southeast Asia (mainly Thailand, Myanmar, formerly known as Burma, and parts of China) and South Asia, which is the biggest by far.

In the case of India, Pakistan, Bangladesh and Nepal, temperatures build over the South Asian subcontinent during the late spring and summer months, creating a low pressure system over the land that draws in the cooler moist air from the Indian Ocean and Arabian Sea.

In some years, when summer temperatures in India exceed 45 C, the temperature differences between the land and nearby Bay of Bengal can be 20 or so degrees and this meteorological imbalance draws the wet air inland at a great clip until it hits the Himalayas, rises and drops its load in an almost daily rainfall that can last from late June until September, when it reverses itself.

Then dry air from the interior flows out towards the surrounding oceans from mid-September until around March when the cycle starts all over again.

A way of life

Though, for the most, the rainy season arrives like a welcome friend in South Asia, every year the pattern and overall amount of precipitation is different. That accounts for the higher than usual losses of life in some years, when the rains hit areas that are off the beaten path or are unprepared for the downfalls. (Both India and Pakistan called out their armies in July to help with the flooding. Nepalese authorities have said their biggest problems are in areas made inaccessible by road closures.)

The monsoons — and monsoon forecasting — are very important to South Asia as this is an area that is highly dependent on agriculture. In India, for example, nearly two-thirds of the workforce is engaged in farming and agriculture accounts for roughly 25 per cent of the country's GDP.

If the monsoons are predicted to be late, farmers (fearing a drought) tend not to plant as much as in other years and this can have a huge affect on financial markets as well as the country's ability to feed itself.

As a result, the meteorological forecasts in April and May are parsed and watched with the kind of interest that Canadians might reserve for hockey playoffs.

The June rains tend to be welcome in the region where they can herald a bountiful harvest and cool the cities. (The Times of India reports that monsoon season is the hottest party and fashion season.)

But every year they also lead to usually quite widespread displacement of rural families and loss of life through flash floods, landslides or water-borne diseases such as dysentery.

This year's tally — 1,900 dead and 28 million temporarily homeless — seems higher than normal. Last year saw about 300 deaths resulting from monsoon flooding in India, Pakistan, Bangladesh and Nepal. In 2005, the number was just over 1,000; in 2004, 2,208; and in 2003, 1,500, all according to news reports.

While the numbers seem high, they still pale beside the many deaths attributed to drought when the rains don't come on time or the cyclone-induced flooding at other times of the year, which has devastated the coastal regions of Bangladesh in particular.