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PRECIPITATIONS
AND
FLOODINGS

4st PART

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PRECIPITATIONS

TYPES OF PRECIPITATIONS

THE FLOODS


WHERE ARE THE MOST FREQUENT ?

- IN FRANCE :

In France, floods are the most recurring climatic event. 5-7.% of French territory is likely to be flooded, about 10.% of the population. On the 160.000 km of rivers which flow into France, there is an area of 22.000 km2 would be particularly recognized flood, spread over 7.600 towns therefore 2.000.000 residents would be affected.

Click here to enlarge map

IN THE WORLD :

Floods are natural climatic event the most common in the world and can occur in all parts of the world, it is a natural phenomenon that affects the most human. If they are so frequent this is because many factors can trigger floods.

Cyclones are one of the leading causes of flooding and affect mainly subtropical and intertropical latitudes.

Click here to see where flooding now occurs

(source : Darmouth Flood Observatory)

MONSSOON

The seasonal alternation of winds at subtropical and tropical latitudes trigger monsoons in Africa, Indian Ocean, south and east Asia so 50% of the population is affected. Every year in summer the precipitations created devastating floods.

Monsoon in the world

In India, where they are the most important it can fall up to 3 cm of water in 5 minutes during the monsoons that last 3 months. It is in this country that one notes the highest rainfall rates in the world, there are more than 600 cm of rain per year in some cities. During the half of the winter, dry and fresh air coming from Asia moves towards South West of the India, making reign a dry and sunny climate. But from the end of May because the temperature rises above the Tibet warm air from the Indian Ocean leads to heavy rainfall across India.

 

In India, Bangladesh and South China the floods
are so important during the monsoons that entire villages
are flooded and often peoples must move by boat

 

Floods can be more or less important every year according to the ENSO phenomenon (El Nino and La Nina) and places.

When the El Niño phenomenon appears precipitations are more important throughout Eastern America (Chile, Peru, Northern Brazil, Mexico and some states of the USA), Cuba and Ethiopia, which often causes floods.

For precipitations, La Niña has effects on : stronger monsoons in the sub continent Indian, torrential rains causing floods in the South East Asia and Africa and in the East and North of the Australia.

The three components of the monsoon system are linked to warming of the ground
(desert and rainfed areas), regions of warm tropical oceans and those cold mid-latitude
oceans. All these conspire to produce the highest heating inclinations on Earth.There are
three main cells associated with boreal and austral summer monsoons. These are the transverse
and lateral components, and the Walker cell. Together, they form a simplified view that
includes atmospheric monsoon currents associated with El Nino in the Indo-Pacific region.

During a classic episode of El Niño, the monsoon is less important in India and descends towards the equator, resulting even in drought conditions in the summer in the Centre and Northwest of the India and heavy rains in the Northeast. But when a positive IOD (Indian Ocean Dipole) event takes place at the same time then it can cancel the effect of El Nino.


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