A deluge is defined as a very heavy fall of rain or a severe flood. The most well known deluge was in pre-history, during the great flood when Noah build his ark. That was when it supposedly rained solidly for 40 days and 40 nights.
It has been calculated that if the total rainfall over the Earth were averaged out, each place would get something like 800 millimetres of rain a year (around 34 inches).
Rainfall varies enormously, of course. One of the wettest places in the world is Cherrapungi in northeast India where, in 1861, the annual rainfall reached 26,000 millimetres (over 1000 inches). It regularly gets over 10,000 mm (430 inches) every year.
The most intense rainfall ever recorded was on the 26 November 1970 on the Caribbean Island of Guadeloupe where 38.1 mm or 1.5 inches fell in just one minute. Whereas over a complete 24 hours, Reunion, in the Indian Ocean, recorded 1,850 mm (73 inches) in March 1954. And at Mount Wai-ale-ale in Hawaii they have up to 350 days rainy days each year.
These heavy rains fall for two reasons. Firstly, the southern Asian southwest monsoon. And secondly super-cells within cumulonimbus clouds which can be associated with hurricanes, tornadoes or severe thunderstorms.
These large thunder clouds are formed as warm, moist air rises quickly forming up draughts of air and compensating downdraughts. But in a super-cell there is only one up and downdraught which allows the cloud to grow much larger than normal giving much heavier rain. The rainfall can be as much as 200mm in an hour, or some eight inches. Such deluges give rise to flash floods and mudslides.
It is the super-cells within the tropical cyclones, such as hurricanes or typhoons that produce the very heavy downpours as these storms start to move inland. In the southwest monsoon, on the other hand, the rain can be nearly as heavy and last for a long period of time.
In the northern summer, high pressure over the Indian Ocean and low pressure over continental Asia pulls in very moist air from the Arabian Sea and the Bay of Bengal. This provides both life sustaining rains, as well as life threatening deluges and floods. And this is why, at the base of the Himalayas, Cherrapungi is one of the wettest places on Earth. It's beaten only by its near neighbour Mawsynram, which has an annual rainfall average of 11,430 mm (450 inches). And most of this falls between June and November!
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