Effect of Relief

Effect of Relief The rain-laden winds from Arabian Sea bring orographic rainfall in Konkan coast and Western Ghats (about 250 em). The leeward side receives only 37­75 em rainfall as it falls in the rain-shadow area. Thus TamilNadu gets no rain.

Distribution of Rainfall Except for Thar, north-west region of Jammu and Kashmir and some areas of Tamil Nadu, the rest of the country receives rainfall from south­west monsoon. 200 cm and above-Western Ghats and North-eastern region. 100-200 cm-West Bengal, Orissa, Bihar, Jharkhand, Andhra Pradesh, Kashmir foothills, Tamil Nadu coast. Less than 100 cm-Rajasthan, Punjab, western Uttar Pradesh, western Madhya Pradesh and Deccan pla­teau.

Variability of Annual Rainfall One of the important characteristic features of the monsoon is its variability. There may be a deviation by 20 to 50 per cent in the actual rainfall of a place in a year.
The variability of rainfall may be calculated with the help of the following formula:
C = (Standard deviation/Mean) x 100

where C is coefficient of variation.

The value of C indicates the deviation from the mean value of rainfall. In India, the coefficient of variation generally ranges between 15 and 30 per cent. The coefficient of ~ariation in places such as Mangalore, Sikkim, Arunachal Pradesh, Nagaland, Manipur and Mizoram is less than 15 per cent. On the other hand, it may be as high as 30 per cent in the interior regions of Maharashtra, Andhra Pradesh and Karnataka. So is the case with southern Gujarat, western Madhya Pradesh and central parts of Uttar Pradesh. The variability of rainfall over Rajasthan and Gujarat is over 40 per cent, while the desert areas of Rajasthan and parts of Kutch and Gujarat may have a rainfall variability ranging between 50 and 80 per cent.

Variability of rainfall plays a crucial role in Indian agriculture. Areas having high variability of rainfall suffer from a chronic water scarcity. Crop failures are common in such areas. These areas also experience spells of drought frequently.