Cherrapunji is a subdivisional town in the East Khasi Hills district in the Indian state of Meghalaya. It is credited as being the wettest place on Earth, but nearby Mawsynram currently holds that record. Cherrapunji still holds the all-time record for the most rainfall in a calendar month and in a year. It received 9,300 mm (366 in) in July 1861 and 26,461 mm (1,041.75 in) between 1 August 1860 and 31 July 1861. Cherrapunji is the traditional capital of the Nongkhlaw hima (Khasi tribal chieftainship constituting a petty state) known as Sohra or Churra. Cherrapunji is also famous for its living bridges. Over hundreds of years the people in Cherrapunji have developed techniques for growing roots of trees into large bridges. The process takes 10–15 years and the bridges typically last hundreds of years, the oldest ones in use being over 500 years old. Cherrapunji receives rains from the Bay of Bengal arm of the Indian summer monsoon. The monsoon clouds fly unhindered over the plains of Bangladesh for about 400 km. Thereafter, they hit the Khasi Hills which rise abruptly from the plains to a height of about 1,370 m above mean sea level within 2 to 5 km. The geography of the hills with many deep valleys channels encompassing the low-flying (150–300 m) moisture-laden clouds from a wide area converges over Cherrapunji. The winds push the rain clouds through these gorges and up the steep slopes. The rapid ascent of the clouds into the upper atmosphere hastens the cooling and helps vapours to condense. Most of Cherrapunji's rain is the result of air being lifted as a large body of water vapour. The extreme amount of rainfall at Cherrapunji is perhaps the best-known feature of orographic rain in northeast India. Occasionally, cloudbursts can occur in one part of Cherrapunji while other areas may be totally or relatively dry, reflecting the high spatial variability of the rainfall. Atmospheric humidity is extremely high during the peak monsoon period. The major part of the rainfall at Cherrapunji can be attributed to the orographic features. When the clouds are blown over the hills from the south, they are funneled through the valley. The clouds strike Cherrapunjee perpendicularly and the low flying clouds are pushed up the steep slopes. It is not surprising to find that the heaviest rainfalls occur when the winds blow directly on the Khasi Hills. A notable feature of monsoon rain at Cherrapunji is that most of it falls in the morning. This could be partly due to two air masses coming together. During the monsoon months, the prevailing winds along the Brahmaputra valley generally blow from the east or the northeast, but the winds over Meghalaya are from the south. These two winds systems usually come together in the vicinity of the Khasi Hills. Apparently the winds that are trapped in the valley at night begin their upward ascent only after they are warmed during the day. This partially explains the frequency of morning rainfall. Apart from orographic features, atmospheric convection plays an important role during the monsoon and the period just preceding it.
