Mawsynram and Cherrapunji

Wettest Place in the World: Mawsynram

By: Ajit Tyagi and P Guhathakurda
Mawsynram, has currently overtaken Cherrapunji as the wettest place on earth. But both these places in Meghalaya’s East Khasi hills share a common orography, although facing different valleys.
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Mawsynram and Cherrapunji, which place is the wettest ? Records—sports, music, cooking or even rainfall always generates curiosity. But, there is this thing about records—it is almost always broken by a new one. Thus, Cherrapunji’s record as the wettest place in the world has been overturned with Mawsynram figuring as the ‘latest’ wettest place on earth.

Locally known as ‘Sohra’, Cherrapunji is located in the East Khasi Hill district of Meghalaya in northeast India. Weather observations ranging from as far back as 1902, when climatic record keeping began in the region, placed Cherrapunji on top where rainfall was concerned. Climatic records such as the wettest place are based on ‘climatic normals’ in relation to a given reference period. The first climatological normals published by the India Meteorological Department (IMD) for 1901-1940 showed Cherrapunji as the wettest place in India with an annual rainfall of 10800.8 mm. Measurement of rainfall at Mawsynram, which is 16 km away from Cherrapunji started from June 1940.

In a study by V Thapliyal and S M Kulshrestha using 26 years of available rainfall data from 1941-78, the average annual rainfall of Mawsynram at 11873 mm, was found to be higher than Cherrapunji’s 11763 mm for the same period. The Guinness book of World Records refers to the above value while declaring Mawsynram as the Wettest Place on Earth. The World Meteorological Organization’s extreme record site also shows Mawsynram as the site of Asia’s greatest precipitation.

Subsequently new rainfall normals have been published for 1951-2000 by IMD. The monthly average and annual average rainfall for Mawsynram and Cherrapunji are shown in Tables 1. It is seen that Mawsynram has figures higher than that of Cherrapunji. Annual average rainfall of Mawsynram for the latest period (1951-2000) is 12397.3 mm as against the 11720.3 mm of Cherrapunji. Thus, Mawsynram continues to hold on to the ‘wettest place’ record.

Rainfall in the Khasi hills

Both Cherrapunji (25o15ʹN, 91o44ʹE, elevation 1313 m) and Mawsynram (25o18ʹN, 91o35ʹE, elevation 1401.5 m) are located on the southern slopes of the east Khasi Hills in Meghalaya. Stretching 300 km in length and about 100 km in breadth, Meghalaya is a mountainous state, numerous valleys and highland plateaus. Elevation in the plateau region ranges between 150 m (490 ft) to 1,961 m (6,434 ft), with the central part comprising the Khasi Hills with the highest elevations. Both Cherrapunji and Mawsynram lie in the southern part of the East Khasi Hills overlooking narrow north-south oriented valleys opening to the plains of Bangladesh in the south. The rainfall in Cherrapunji-Mawsynram is caused by the orography favouring a monsoon wind regime. The northward moving moist winds from the Bay of Bengal passing over the plains of Bangladesh are forced to converge in the narrow valleys of the Khasi Hills with orography providing forced ascent that causes condensation, formation of clouds resulting in rain on the windward side of the slope.

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Table 1: Rainfall normals (1951-2000)

Although both Mawsynram and Cherrapunji are located on the southern slopes, they face different valleys. The valley separating Mawsynram and Cherrapunji is drained by the Umiam river, while the valley to the east of Cherrapunji is drained by the Umsohryngkew river. The elevation of Mawsynram is 88.5 m higher than that of Cherrapunji and it is situated on the fringe of the narrow valley with its mouth about 6 km wide open to the south. The 1000 m deep valley is north-south oriented, up to a distance of 9 km where after it turns northeast. Higher elevation and cyclonic curvature of the valley are the probable causes of higher rainfall at Mawsynram.

Mawsynram and Cherrapunji – the wettest?

Since the unique orography of Cherrapunji-Mawsynram is primarily responsible for very high rainfall, the possibility of some other location in the region receiving higher rainfall than Mawsynram can not be ruled out. Therefore, there is need to map southern slopes of Khasi Hills by a dense network of rain gauges and dual pol-doppler weather radar to locate the place of highest rainfall, which will also help in building the understanding of rainfall mechanism better.

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