India, Nov. 17 -- They are akin to aliens in the world of meteorology-unimaginable and unpredictable. And now they seem to be invading. That, at least, was how it felt when cloudburst-like downpours lashed much of India's plains in the monsoon months of August and September.

Meteorologists define cloudburst as rainfall exceeding 100 mm in an hour over an area of 20 to 30 sq km. Such events are typically confined to hilly terrain. But on August 30, the Manali area of Chennai, Tamil Nadu's coastal capital, recorded 106 mm of rain in an hour starting at 10 pm. A second spell, from 11 pm to midnight, brought another 127 mm. In the same hour nearby Wimco Nagar saw over 157 mm of rainfall, Korattur recorded 137 mm, and New Manali received 103 ...