Identifying the changes in rainfall pattern and heavy rainfall events during 1871-2010 over cherrapunji

Abstract

Cherrapunji holds world record of highest recorded point rainfall for different durations i.e. 1 month, 2 months, 12 months, 2 years (WMO 1994). It is situated in the southern slopes of Khasi and Jayantia Hills of ‘Meghalaya’ province of India overlooking the plains of the Sylhet district in Bangladesh. The meaning of Meghalaya is the abode of cloud. The altitude of Cherrapunji (Fig. 1) is 1,313 m above mean sea level. Rain occurs almost regularly throughout the year over this region due to its peculiar orographic features. Synoptically, this region is the convergence zone of westerly, easterly and moist southerly winds causing lots of rain and therefore the average monthly rainfall is also very high over this region. The monsoon clouds fly unhindered over the plains of Bangladesh for about 400 km. Thereafter, they hit Khasi hills which abruptly erupt out of the plains to reach a height of about 1,370 m above m.s.l. within a short distance of 2-5 km. The orography of the hills, with many deep valleys, channels the low flying (150-300 m) moisture laden clouds from a wide area to converge over Cherrapunji which falls in the middle of the path of this stream. The winds push the rain clouds through these gorges and up the steep slopes. The rapid ascendance of the clouds into the upper atmosphere hastens the cooling and helps vapour to condense. Most of Cherrapunji’s rain is the consequence of air being lifted as a large body of water vapour. Extremely large amount of rainfall at Cherrapunji is perhaps the most well-known feature of orographic rain in northeast India.