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Pakistani Floods

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The Pakistani Floods of 2010
by The British Geographer

The Causes of the Flood
Physical Causes
From its headwaters in the Himalayas of Tibet, the River Indus flows northwest through India before turning sharply south across Pakistan. It finally discharges into the Arabian Sea, a journey of some 3,200km (2,000 miles). The River Indus has an annual flood caused by tropical monsoon rainfall. It’s rich alluvium floodplain led to one of the cradles of civilization, 9000 years ago.  However, this flood’s magnitude was according to Professor Rajiv Sinha, from the Indian Institute of Technology, 5 or even 10 times stronger than normal. The annual monsoon is caused by the movement of warm moisture laden air from the Indian Ocean toward areas of low pressure, marked out by the Inter-Tropical Convergent Zone (ITCZ) over the subcontinent. Here, the subcontinent is superheated, which creates strong rising thermals of low pressure. As warm air moves over the subcontinent it rises and dumps vast quantities of rainfall, which cools the surface and replenishes the vital soil moisture and ground water. In July 2010, more than half the normal rains fell in just one week in an unprecedented sequence of days. Intense rainfall totaling in excess of 200mm fell in a 4-day period from 27th to 30th July along with above average rainfall in August. The recorded monsoon rainfall associated with La Nina was the highest in a 50-year period.

The total area affected by flooding was 796,095 square kilometers, approximately one fifth of Pakistan’s total land area

 

There was much discussion over the exact causes of this level of rainfall. La Nina, which is a coupled ocean-atmosphere phenomenon that impacts southeast Pacific Ocean temperature but is also thought to increase Indian monsoon rainfall was thought to be a contributing factor. The cycle of El Nino and La Nina, which are both important global heat transfers seems to be occurring more frequently and is potentially a...