Thursday 17 August 2017

Flooding in Bihar State, India, kills at least 98.

At least 98 people have died and over seven million have been forced to flee their homes in flooding across the state of Bihar in India this week. Twenty people are known to have died in Araria District, fourteen in East Champaran, thirteen in West Champaran, twelve in Madhepura, eleven in Sitamarhi, eight in Kisanganj, five each in Purnea and Madhubani, four in Darbhanga, three in Saharsa, two in Sheohar and one in Supual. The flooding has left many more without access to food and clean water, and washed away many roads and railways, leading the Indian National Disaster Response Force to drop supplies by air in areas where local populations cannot be reached in any other way.

People affected by flooding in Bihar State, India, this week. Times Now.

The flooding has been triggered by heavy rainfall in Nepal, associated with the Asian Summer Monsoon, which has caused the Koshi, Mahananda, Gandak, Bagmati and Ganga rivers to swell and breach their banks in many places, and made worse by high rainfall across Bihar itself.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea. 

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

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