Wettest places in India

By incorporating data from unofficial, non-reporting raingauge stations a list of locations with an average annual rainfall exceeding 5000 mm can be compiled for India. All stations are located along the westward exposed escarpment of the Western
Ghats at a distance of not more than 100 km from the Arabian Sea. Here the superimposition of la~'ge-scale dynamic and static, locational "controls" during the Southwest Monsoon period (June-September) results in annual, monthly and daily rainfall amounts that are only surpassed at a few stations outside the peninsula in Northeast India. The fourteen rainfall stations (see Fig. 1) whose mean annual rainfall is 500 cm (i.e. 200 inches) or more.Among these fourteen stations, there are only two stations (viz. Cherrapunji and Mawsynram) whose mean annual rainfall is more than 1100 cm. These fourteen stations have been called the rainiest stations of this country.

In addition to the heavy rainfall stations listed 7 other locations(with a minimum of 10 and up to 39 years' continuous records) were found to receive over 5000 mm of rain per year on an average. However the figures are not strictly comparable since they do not relate to identical observation periods; nevertheless, they indicate those areas in Peninsular India where rainfall of such quantity and intensity can be expected.

The most conspicuous feature regarding the spatial distribution of the 17 heavy rainfall stations in Peninsular India (Fig. 1) is their alignment along the westward exposed slopes of the Western Ghats (or Sahyadri Range) within a distance of not more than 100 km from the Arabian Sea and in close proximity to the (asymmetric) subcontinental "divide" or watershed which runs parallel to the west coast of the peninsula. While 9 stations are located at the western edge of the Deccan in Maharashtra and Karnataka, the remaining stations represent heavy rainfall areas in the "mountain blocks" of 'Tamil Nadu and Kerala further south: 4 in the Nilgiris, the junction of the Western and Eastern Ghats culminating in Dodabetta (2636 m), 3 in the High Range (or Kanan Devan Hills) next to Anaimudi (with 2695 m the highest peak in India south of the Himalayas) and finally Peermade in the Cardamom Hills, about 75 km from the Kerala coast.

Another characteristic of all stations falling into the "heavy rainfall" category as defined above is revealed by studying their annual rainfall pattern: a long dry season from November to April/May in the north and from December to March/April in the south, i. e. during the Northeast Monsoon period when "tropical easterlies" (or "trade winds") with large-scale subsidence and stability in the lower and middle troposphere prevail and when depression or cyclonic influences hardly ever reach these tracts of India. Rainfall during the dry season constitutes less than 5% of annual precipitation. At Mahabaleshwar, for instance, the average from November through April, for half the year, just reaches 100 mm and accounts for only 1.5% of the annual total.

Thus precipitation in the heavy rainfall areas in Peninsular india is mainly based on rainfall during a comparatively short rainy season. This "seasonal concentration" is the result of dynamic (weather) "controls" and locational factors interacting during the course of the annual monsoonal rhythm, the alternation of dry weather conditions during the Northeast Monsoon and the "rain-producing" synoptic patterns during the Southwest Monsoon.

Source:H. J. von Lengerke, South Asia Institute, University of Heidelberg, Germany
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