By Kate Larkin

It is over two weeks since the floods began in Pakistan, and the rains are still falling. Already termed the worst flooding to hit Pakistan for 80 years, this deluge has affected millions of people, and so far over 1,600 have died.

With the impacts of the flooding likely to continue well after the flood waters have retreated, Nature examines the escalating humanitarian disaster. (Scientific American is part of Nature Publishing Group.)

What is the main cause of the intense rainfall?

It is weather, not climate change, that is to blame, according to meteorologists. An unusual jet stream in the upper atmosphere from the north is intensifying rainfall in an area that is already in the midst of the summer monsoon (see animation showing the growing extent of the flood waters). "What sets this year apart from others is the intensity and localization of the rainfall," says Ramesh Kumar, a meteorologist at the National Institute of Oceanography, Goa, India. "Four months of rainfall has fallen in just a couple of days."

Has human activity exacerbated the flooding?

Yes. The high population growth rate in Pakistan has contributed to a rapid deterioration of the country's natural environment. This includes extensive deforestation and the building of dams for irrigation and power generation across tributaries of the Indus River. Years of political unrest have also left their mark, and flood waters are transporting land mines, posing an extra danger to the relief mission.

Is the humanitarian crisis larger than the 2004 Asian tsunami, as some media reports have claimed?

Not in terms of the death toll. With 1,600 people reported dead, this remains 100 times less than the 2004 Indian Ocean tsunami. However, the scale of the tragedy continues to increase, with around 14 million people in immediate need of emergency aid. Many of Pakistan's bridges and roads have been destroyed, and severe weather is grounding helicopters, slowing relief efforts.

On August 11 the UN and its partners launched an appeal for aid, and the World Bank has announced a grant of $900 million for relief and reconstruction.

What about disease?

The harsh reality is that waterborne diseases are linked to floods--and with cholera outbreaks reported in the northern Khyber Pakhtunkhwa province of Pakistan, this flooding event seems to be no exception. The fear is that a lack of sanitation will see the fatal diarrheal disease spreading. And stagnant water may pose other threats. "The Pakistan floods and stagnant waters may also cause an increase in malarial cases," says Sandy Cairncross, public health engineer at the London School of Hygiene & Tropical Medicine.

How can Pakistan prepare for floods in future?

"There is currently no effective water management strategy to speak of in Pakistan," says Shah Murad Aliani, country representative for the International Union for Conservation of Nature in Pakistan.

Such a strategy will include building adequate flood defenses along the Indus River, where most of southern Pakistan's population live, and improving flood forecasting systems. International efforts on this front include the European Commission Joint Research Centre, which is developing and testing a Global Flood Detection System to monitor the floods from space.

How will climate change affect the region in future?

"As the atmosphere gets warmer, the carrying capacity for moisture will increase," says Kumar. Put bluntly: if Pakistan's climate warms in the future, rainfall will increase.

There already seem to be more extreme rainstorms than ever before across the Indian subcontinent. A 2006 study indicated that this trend may be set to continue--though the researchers did not unequivocally link this to climate change1.

But many researchers believe that the present flooding may be part of a longer-term trend. "Climate change will be a small but steady contributor to rainfall in the region," says Jeff Knight, climate variability expert at the UK Met Office Hadley Centre.