From Nature:
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.
What is the main cause of the intense rainfall?
It is weather, not climate, 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 localisation 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.
More here.