Page last updated at 15:37 GMT, Friday, 31 July 2009 16:37 UK

Uncertainties surround future monsoons

By Navin Singh Khadka
Environment reporter, BBC News

Children playing in the rain (Image: BBC)
Some scientists fear climate change will adversely affect the monsoon season

It is almost halfway through the rainy season, and the monsoon in many parts of South Asia continues to remain unreliable.

In some places it has been crippling weak, while in others it has been devastatingly intense.

There are places reeling from drought, yet at the same time there are areas that have been hit by torrential rains, triggering floods and landslides in a very short span of time.

This has made the lives of millions of people difficult and has left them increasingly worried for the future.

Very little of the arable land is irrigated, and local populations depend on monsoon rainfall for agriculture.

Freshly planted crops awaiting monsoon rains (Image: Madhav Nepal/BBC)
Crops in the region are dependent upon the annual monsoon rains

The monsoon clouds have weakened in several parts of the region and the variable and erratic rains have left weather forecasters scratching their heads.

This failure of the monsoons to behave as expected has led to the question of whether climate change is to blame.

Experts differ on whether these changes are directly linked to climate.

"This year's monsoon behaviour cannot yet be attributed to climate change as it is still within the observed natural variability of the monsoon," said Krishna Kumar Kanikicharla, a scientist at the Indian Institute of Tropical Meteorology.

"Our assessment of climate model simulations for the current and the next century indicate no significant deviation until the middle of the 21st Century. Thereafter, the monsoon rainfall will continue to increase by 8-10% from current levels."

A regional research centre in Bangladesh found what it called "cyclic changes", but has identified no effects so far that can be attributed to climate change.

A gloomy forecast

The South Asian monsoon normally begins in June and lasts around four months. The Indian Meteorological Department in April had forecast an optimistic 96% of long-term average rainfall.

Rice saplings drying out as a reuslt of a lack of rain (Image: Madhav Nepal/BBC)
Without the rains, young crops soon perish and die

But in the last week of June, by which time the monsoon clouds should normally have moved northward from the Indian ocean, they were hardly moving.

With farmers in Northern India postponing their crop plantations and authorities cutting the supply of stored water for irrigation, the government had to scale down its rainfall forecast to 93% of the long-term average rainfall.

In neighbouring Bangladesh, the situation was even worse; it saw 80% lower rainfall than what would normally be the case.

An unusually long dry spell fanned several wildfires earlier this year. Nepal too saw delays in the arrival of its precious monsoon clouds.

When they reached northern areas of the region by the third week of July, many places began to see heavy precipitation.

Bangladesh's capital, Dhaka, saw more than 33cm of rainfall in about 24 hours - the greatest amount for many years.

Floods have wreaked havoc in many parts of north-east India, and nearly three dozen people have died in Nepal as a result of monsoon-triggered landslides.

At least another dozen are missing from remote Nepalese mountain areas.

Yet many areas in this region still remain parched.

Until the middle of this week, northern and south-western parts of Bangladesh have had about 40% lower rainfall than the average.

Some parts of northern India have been declared drought-hit by local governments.

Almost the same is the case in eastern Nepal, where rainfall is around 50% lower than normal.

Meteorological officials in Pakistan say most parts of the country have remained more or less dry, with average rainfall limited to only 50% of normal precipitation.

"Even where it has rained, the rainfall is around 30% lower than normal," said Qamar Zaman Chaudhary, director-general of Pakistan's met office.

"Figures [from recent years] show that monsoon rainfall is gradually decreasing - year on year."

Patchy cloud

Over the past five years, even though total rainfall has not deviated far from the average in these countries, the distribution has been quite uneven.

A farmer (Image: Madhav Nepal)
Farmers could struggle to keep their crops alive

Some places have experienced heavy rainfall while others have seen far smaller amounts of rain and have been hit by drought.

And dangerously unpredictable rainfall such as that which claimed hundreds of lives in Mumbai in 2005 is on the rise.

In yet another unusual development, places that received smaller amounts of rainfall have begun to receive more rain. While what used to be relatively wet areas are now becoming drier.

Some researchers suggest that this is a natural "shift" in the pattern of rainfall.

"We studied three 30-year window periods from 1951 to 2000 and found that there was a slow shift in the rainfall scenarios," said Sujit Kumar Deb Sarma, a researcher with the South Asian Association for Regional Cooperation (SAARC) Meteorological Research Centre in Bangladesh.

"Places that got more rain are receiving lower rainfall and vice versa.

"But we also found that after some time the rainfall patterns go back to what they were before and slowly start changing again. It's a cyclic change that has been happening [for] years."

But authorities in Pakistan believe the falling monsoon rainfall may have been the result of climate change.

"There may have been some impacts of climate change," said Mr Chaudhry of the Pakistan Met Office.

"We know that the El Nino events have been affecting our rainfall all these years, but climate change could be aggravating the situation even more."

Meteorologists in Nepal too think global warming may have some role in the changing monsoon pattern the country has been experiencing.

"There are so many factors including the El Nino effect that have been affecting the monsoon but we cannot say that these changes are not because of global warming," said Mani Ratna Shakya, head of the weather forecasting division.

Traffic in the rain (Image: BBC)
The monsoon season is welcomed by most people in an otherwise arid region

International studies have also pointed at the relationship between the monsoon and climate change.

A study by researchers at Purdue University, US, found that the South Asian monsoon could be weakened and delayed as a result of rising temperatures in the future.

"Climate change could influence monsoon dynamics and cause lower summer precipitation, a delay to the start of the monsoon season and longer breaks between the rainy periods."

Another report recently prepared for the Australian government has shown that potentially greater threats could be abrupt changes to the oceans and atmosphere that lead to irreversible switches in weather or ocean patterns - so-called tipping points.

"An example is the Indian monsoon. According to some models that could switch into a drier mode in a matter of years," the report's author Will Steffen, executive director of the Climate Change Institute at the Australian National University, told Reuters.

The fourth assessment report of the IPCC had this to say about the monsoon: "It is likely that warming associated with increasing greenhouse gas concentrations will cause an increase of Asian summer monsoon precipitation variability.

"Changes in the monsoon mean duration and strength depend on the details of the (greenhouse gases) emission scenario."

Do the changes mean weather forecasters will have a tough time ahead predicting the monsoon as they have had this year?

Indian Meteorological Department chief BP Yadav admitted that could be the case: "There are already some indications of increase in the variability of weather parameters, so when you have a high variability in any events like rainfall or temperature, definitely the work of predicting them becomes more difficult," he said.

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