The need for irrigation in India arises out of following reasons-
1. Uneven Distribution of Rainfall
In India the average of annual rainfall is 100 cm which is not uniform throughout the country. Whereas Western Ghats and eastern India receive more than 250 cm of annual rainfall; the Northern plains and the eastern Peninsula between 100 and 200 cm; there is a vast area in the western part of the country and rain shadow zone of the Sahyadris where average annual rainfall is less than 60 cm. In the arid parts of Rajasthan and in Ladakh (Jammu and Kashmir) the annual amount of rainfall is less than 25 cm. Lower amount of rainfall is characterised by higher variability necessitating the use of irrigation water to carry on agricultural operations.
2. Uncertainty of Rainfall
India’s rainfall is highly variable in place and time. Major part of the country records more than 25 per cent of variability and in western part it goes beyond 60 per cent. High variability leads to greater incidence of famines and droughts. According to one estimate drought and famine occur at an interval of 6 years leading to the failure of crops and great exodus of the people. Hence, irrigation is the only solution to reduce the severity of the droughts and protect agricultural crops.
3. Irregularity of Rainfall
There is no fixed time for the beginning and end of the rainfall. Sometimes monsoon arrives early but sometimes it becomes late. There is no regular rainfall throughout the rainy season. Often there is long dry spell during the rainy season which creates water scarcity and withering of the crops. Sometimes even the axis of monsoon changes leaving out a long strip of land deficient in rainfall. This can be mitigated through effective and dependable sources of irrigation.
4. Seasonality of Rainfall
In India over 90 per cent of the rain is obtained during second half of the summer season. The duration of rainy season decreases from 6 months in Assam to 2.5 months in north-west India. Hence, irrigation is the only means to supplement rain water to raise crops.
5. Multiplicity of Crops
India has three cropping seasons, kharif, rabi and zaid. Kharif is a rainy season crop solely dependent on monsoon rains. These are the crops which occupy largest area in the country. Where irrigational facilities are not developed these crops are grown as rained crops. Rabi crops are raised on the soil moisture left after the harvest of kharif crops or grown over the area where assured irrigation is available. Except a meager amount of rainfall through western disturbances in the north-western parts of the country during winter season and some precipitation along the Tamil Nadu coast by retreating monsoon these crops are mainly irrigated crops. Zaid or summer crops are exclusively irrigated crops.
The growing pressure of population has compelled farmers to go for two or three successive crops in a single year which cannot be done without the help of irrigation.
6. Specialty of Crops
Different crops require different quantities of water for their growth. Millets, barley, pulses generally need less water while rabi crops like wheat, potatoes, kharif rice and cash crops like sugarcane, cotton and tobacco etc need higher quantity of water. High yielding varieties using higher dosage of chemical fertilisers require more moisture which could be met only through irrigation.
7. Commercialised Crops
Commercial crops providing 33% of the total value of agricultural crops and occupying about 20% of the total cropped area of the country require assured irrigation to improve the quality and quantity of their production. These crops which earn valuable foreign exchange need frequent watering which could be managed through efficient irrigation system.
8. Nature of the Soil
The need for irrigation is very much linked with the nature of the soils. Sandy loam, which has less retentive capacity of moisture, needs frequent watering. On the other hand clay soils have higher moisture holding capacity and require less irrigation. Sloppy surface and highland areas require more watering than level and lowland areas.