This is a joint post with Wren Elhai, and first appeared on Foreign Policy's AfPak Channel.
"Heart-wrenching," said U.N. Secretary General Ban Ki-Moon Sunday upon surveying Pakistan's ongoing floods. The U.N. chief called the floods "the worst natural disaster" he said he had ever seen. The numbers explain why. More people have been affected by Pakistan's catastrophic floods than any other natural disaster on record -- over 20 million and counting. That's more than were affected by the 2005 Pakistan earthquake, the 2004 Asian tsunami, and this year's earthquake in Haiti combined. As millions of dislocated Pakistanis search for shelter and food and as health conditions deteriorate and disease spreads, the need for an immediate, large-scale humanitarian response is urgent. And this is just the beginning. Once the floodwaters subside from Pakistan's swollen rivers, the task of rebuilding will be staggering - with a price tag in the billions, and lasting for years to come. The effectiveness of the response to these relief and rebuilding challenges will have serious implications for the wellbeing of the country's citizens, for the peace and stability of Pakistan and the entire South Asian region, and for U.S. national security.