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.

Kerala floods: heavy monsoon rains lead to deaths in India Show all 40 1 /40 Kerala floods: heavy monsoon rains lead to deaths in India Kerala floods: heavy monsoon rains lead to deaths in India A man removes debris from a collapsed house after floods in Paravur Reuters Kerala floods: heavy monsoon rains lead to deaths in India An ariel shot of Kerala from Thiruvanpuram Getty Kerala floods: heavy monsoon rains lead to deaths in India Murgan and his family clean up their house in Mundancavu village at Chegannur upon returning home after the flood waters receded Getty Kerala floods: heavy monsoon rains lead to deaths in India People assess damage caused by floods on the outskirts of Kochi AP Kerala floods: heavy monsoon rains lead to deaths in India Men paddle their boat through the lawns of a partially submerged church at Kuttanad in Alleppey district Reuters Kerala floods: heavy monsoon rains lead to deaths in India Sandhya Biji and her son in front of their damaged house on the banks of Pamba river Getty Kerala floods: heavy monsoon rains lead to deaths in India Border Security Force distribute food food and water to the residents who are stuck in their houses as well who have not vacated houses because of the flood water in interior places at Allapy Getty Kerala floods: heavy monsoon rains lead to deaths in India A damaged house on the banks of Pamba river Getty Kerala floods: heavy monsoon rains lead to deaths in India Murgan cleaning up his house Getty Images Kerala floods: heavy monsoon rains lead to deaths in India An aerial view shows partially submerged houses at a flooded area in the southern state of Kerala Reuters Kerala floods: heavy monsoon rains lead to deaths in India Murgan and his family clean up their house Getty Images Kerala floods: heavy monsoon rains lead to deaths in India People are airlifted by the Indian Navy soldiers during a rescue operation Reuters Kerala floods: heavy monsoon rains lead to deaths in India People wait for aid on the roof of their house Reuters Kerala floods: heavy monsoon rains lead to deaths in India Indian volunteers and rescue personal evacuate local residents AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India Indian people use a boat to rescue an elderly man in the flooded water in Kochi EPA Kerala floods: heavy monsoon rains lead to deaths in India An aerial view shows partially submerged houses at a flooded area in the southern state of Kerala Reuters Kerala floods: heavy monsoon rains lead to deaths in India An Indian woman watches residents walking through flood streets next to their marooned houses AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India Indian army personal evacuate local residents AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India Indian commuters wade through flooded streets AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India People move past a flooded road in Thrissur AP Kerala floods: heavy monsoon rains lead to deaths in India Water gushes out following heavy rain and landslide in Kozhikode AP Kerala floods: heavy monsoon rains lead to deaths in India Fire and Rescue personnel evacuate local residents in an inflatable boat from a flooded area at Muppathadam near Eloor AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India Indian residents look at the Shiva Temple submerged AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India Roads and houses engulfed in water following heavy rain and landslide in Kozhikode. AP Kerala floods: heavy monsoon rains lead to deaths in India People look at vehicles stuck in the mud AFP/Getty Kerala floods: heavy monsoon rains lead to deaths in India A young man wades through a flooded street in Kochi EPA Kerala floods: heavy monsoon rains lead to deaths in India Rescue operations being conducted at the landslide location at Kuttampuzha AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India An elderly woman is rescued in a cooking utensil AP Kerala floods: heavy monsoon rains lead to deaths in India Local residents look at a partially destroyed house after heavy monsoon rains led to a landslide in Kannappankund AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India An Indian woman sits inside her house immersed in flood waters in Ernakulam district of Kochi AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India Indian fire and rescue personnel evacuate local resident AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India A woman stands at the door of her flooded home in Kochi EPA Kerala floods: heavy monsoon rains lead to deaths in India India residents stand on the shore as Periyar river flooded AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India An Indian man carries a basket of bananas next to houses immersed in flood waters AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India Laborers hailing from northern states wade through flood waters as they shift to higher ground AP Kerala floods: heavy monsoon rains lead to deaths in India Kerala chief minister Pinarayi Vijayan (L) along with opposition leader Ramesh Chennithala (2L) visit relief camp in Chengamanadu Government Higher Secondary School AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India Athirampally Falls EPA Kerala floods: heavy monsoon rains lead to deaths in India epa06939658 A structure is submerged in flood water following heavy rain in Kochi, Kerala state, India, 09 August 2018 (issued 10 August 2018). According to reports, the Indian state of Kerala has been hit by heavy rains, causing floods and killing at least 20 people. Indian Meteorological Department (IMD) has predicted heavy rain to continue on the 10 August. EPA/PRAKASH ELAMAKKARA PRAKASH ELAMAKKARA EPA Kerala floods: heavy monsoon rains lead to deaths in India Indian residents look at houses destroyed by flood waters at Kannappankundu AFP/Getty Images Kerala floods: heavy monsoon rains lead to deaths in India Kochi's International airport apron flooded AFP/Getty Images

“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.