What is the phenomenon of 'cloudbursts'? Explain.

What a cloudburst is

In Indian operational usage, associated with the India Meteorological Department, a cloudburst is typically about 100 mm of rain in an hour over a small area of a few tens of square kilometres. The rain is convective. A tall cumulonimbus has a strong updraft that holds rain and hail. Then a sudden downdraft and collapse unload it. Lightning, gusts and, in mountains, debris flow travel with it. It is mesoscale. It is not a monsoon front painted across a whole State.

The name misleads. The cloud does not “burst”. The precipitation efficiency of a cell becomes extreme for a short time.

• Intensity: The fall is very high millimetres per hour. It is not merely a wet day.
• Scale: The cell covers a few kilometres to a few tens of kilometres. That is why a neighbouring village may stay dry.
• Hazard: Flash flood, landslide and a sudden rise of a nala follow, especially where slopes are steep and channels are clogged.

How and where they form

Warm moist air is lifted rapidly. In the Himalaya, orographic lift on south-facing slopes, a monsoon or western-disturbance moisture feed, and a steep lapse rate build deep convection. If a cell stalls against a ridge, rain accumulates in one catchment. The Western Ghats and, less often, arid hills that meet a monsoon surge can see similar cells. Urban cloudburst-like downpours happen when heat and moisture feed thunderstorms over a city. The classic Indian disaster narrative is still Uttarakhand, Himachal, J&K and the Nepal Himalaya.

Forecasting is hard because the cell is small and short-lived. Satellites and Doppler radar help. A warning may still lag the nala. Land use — roads cutting slopes, riverbed mining, hotels on fans — turns a meteorological event into a catastrophe.

• Orography: Mountains force ascent and can trap a cell.
• Moisture and instability: Monsoon air plus heating aloft or cold air above.
• Human exposure: Settlement on floodways makes the same rain deadly.

Kedarnath (2013) and Leh (2010) are remembered as Himalayan hydro-meteorological disasters. Extreme convective rain and mountain geomorphology combined in both. Each event had its own mix of rain, breach and debris. Both sit in the public meaning of a Himalayan cloudburst country.