Last summer's disastrous Pakistan floods that killed more than 2,000 people and left more than 20 million injured or homeless were caused by a rogue weather system that wandered hundreds of miles farther west than is normal for such systems, new research shows.

Storm systems that bring widespread, long-lasting rain over eastern India and Bangladesh form over the Bay of Bengal, at the east edge of India, said Robert Houze, a University of Washington atmospheric sciences professor. But Pakistan, on the Arabian Sea west of India, is substantially more arid and its storms typically produce only locally heavy rainfall.

The flooding began in July and at one point it was estimated that 20 percent of Pakistan's total land area was under water. Structural damage was estimated at more than $4 billion, and the World Health Organization estimated that as many as 10 million people had to drink unsafe water. [ SCIENCE DAILY ]