Cloudbursts are causing chaos in mountainous parts of India and Pakistan, with tremendous amounts of rain falling in a short period of time over a concentrated area. The intense, sudden deluges have proved fatal in both countries. A cloudburst occurs when a large volume of rain falls in a very short period, usually more than 100 millimeters within an hour over a localized area of some 30 square kilometers. The intense, sudden deluges have proved fatal in both countries. Here's what to know about these complex and extreme weather events.