IMD’s cloudburst definition and the flood-risk meaning of extreme concentrated rainfall
A cloudburst is an extreme rainfall event with very high rain intensity concentrated in a small area over a short time. The India Meteorological Department (IMD) definition used in the study note sets the threshold at at least 10 cm rainfall over about 20–30 sq. km within one hour.
When rainfall intensity crosses this threshold, the ground cannot absorb water fast enough. The result is rapid runoff and flash flooding, where water levels can rise quickly and cause severe damage.
How cloudbursts form: convection and mountain-driven lifting of moist air
Cloudbursts form when warm, moist air rises rapidly. This upward motion is called convection (upward movement of warm air) and can be intensified by orographic lifting (mountains force air to rise).
Rapid ascent builds tall storm clouds called cumulonimbus clouds. Strong updrafts in these clouds can keep raindrops suspended until gravity overcomes the upward currents, after which water falls very quickly.
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