(i) Variability in Rainfall:
Rainfall in India is very uncertain which compels irrigation facilities to be provided.
Normal rainfall is marked by its wide fluctuations in different parts as also variation from season to season and year to year in its quantity, incidence and duration.
(ii) Unequal Distribution of Rainfall:
In most parts of the country, 80% of the annual rainfall is received from June to September from the south-west monsoon. Saurashtra-Kutch region of Gujarat, western half of Rajasthan and parts of Punjab and Haryana are in the arid zone. Condition very close to aridity prevails in the rain shadow tract along the leeward side of the Western Ghats. These areas are to be provided with irrigation.
(iii) To Meet Crop requirements and Soil Needs:
Different crops require different quantities of water supply throughout their growing period making it necessary for irrigation. Sugarcane and rice need more water than wheat and other crops.
(iv) To Maximise Production:
To get high yields and maximum production from land, and to facilitate double and treble cropping, irrigation is a must.
(v) To Get Efficient Use of Utilizable Flow:
Many of the Indian rivers are not perennial and they carry insignificant flows during the Rabi season. The characteristic of central and southern rivers is that about 80 percent to 90 per cent of the annual run off takes place during the 4 months of monsoon rains. The rivers are largely dry during the 8 months of the year making it necessary for the provision of irrigation.
(vi) To Supplement Supply Even in Good Rainfall Areas:
In good rainfall areas irrigation is required mostly as a supplemental need to protect their single crop agriculture against occasional drought. According to the Planning Commission the total water resources are about 178 million hectare meters but because of limitations of physiography, topography, geology, dependability, quality and the present state of technology only a fraction of it could be utilised. It has been estimated that the land area that can be ultimately irrigated is 113.5 million hectares.
State with net Irrigated Area of the Net Sown Area:
I. 60% or Above:
Punjab (92.9%, Haryana, Western UP (68.7%) the Krishna-Godavari Delta and Cauvery Delta.
Bihar (49.4%, Ganga Plains, Kashmir Valley, parts of western Maharashtra, east coast including West Bengal.
III. Less than 15%:
West coast, Southern Bihar, Madhya Pradesh, Karnataka, plains of Gujarat and Rajasthan, Gujarat North-east. The intra-state variation in irrigated area is equally wide. For example most of the irrigated area of Andhra Pradesh is confied to the lower reaches of the Godavari Krishna rivers and other coastal districts.