Kerala floods: What causes flash flooding and why has it been so severe in India?

Intense monsoon rains leave 360 dead and 1m displaced in southern state

Joe Sommerlad
Tuesday 21 August 2018 14:28 BST
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Kerala floods: Footage shows destruction as landslides hit region and homes are evacuated

Heavy flooding has caused the deaths of at least 360 people in Kerala since June, the worst natural disaster to strike the southern Indian state in decades.

More than 1m people have been displaced and are recovering in relief camps after 80 dams were overrun by torrential rains.

There have also been significant fatalities in the states of Uttar Pradesh, West Bengal, Maharashtra, Gujarat, Assam and Nagaland as a result of people drowning in floodwater or killed by falling rocks from landslides, caused by running streams unsettling the earth.

At the same time, 11 hikers in Italy were killed when sudden floods swept into the deep Raganello Gorge in Calabria’s Pollino National Park.

Flash flooding has been blamed for both tragedies, but what precisely is it?

The phenomenon occurs when a sudden downpour proves so heavy that the underlying ground cannot cope with the sheer amount of water it is exposed to and becomes saturated before it has a chance to drain away.

Common in low-lying areas, flash floods can also be caused by an intense concentration of rain from thunderstorms on dry soil, unaccustomed to ready absorption.

Just six hours of rainfall can be enough to overwhelm the earth.

In built up areas, this can means sewers overflow and the streets gush like rivers, ferrying debris and in extreme cases running with enough water to lift and carry away cars.

Ordinarily, the flooding of rivers is a very gradual process as it takes time for enough rainfall to percolate through the ground and cause the water level to rise sufficiently so that it overflows before reaching the sea.

Flash flooding, however, gives no such warning.

In the case of Kerala, the weather is part of the four-month monsoon rainy season that strikes the Indian subcontinent every summer.

Local officials have been blamed for exacerbating the situation by failing to gradually open the dams dotting the state’s complex river network, waiting instead until they were already full before unleashing the excess water.

“This could have been avoided if the dam operators had started releasing water in advance rather than waiting for dams to be filled up, when they have no alternative but to release water,” water expert Himanshu Thakkar told the BBC.

India’s Central Water Commission has also been under fire for failing to introduce a flood forecasting system to issue warnings.

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