Rainfall, Its Distribution And Its Effectiveness In Rainfed Agriculture
Distribution of Rainfall: – The amount of rainfall received at periodic intervals like weeks, months, seasons etc. indicate distribution. In addition distribution of rainfall can be known by the length of dry spell, wet spells land rainy days. Distribution of rainfall is more important than total rainfall.
Rainfall pattern at three locations:-
Annual rainfall (mm)
Seasonal rainfall (mm)
Coefficient of variation%
From the above data the growing season is slightly less at Hyderabad as compared to Solapur, However rainy season crops are more successful at Hyderabad and annual yields range 50 to 70 q/ha. While at Solapur and Dhule rainy season crops are risky and annual yields range from 10 to 12 q/ha. Low yields at Solapur and Dhule are mainly due to discontinuous rains or long breaks in rainfall during crop growth period.
Rainfall distribution is based on:
1. Weekly or monthly rainfall will give distribution of rainfall in weeks during a crop season.
2. Wet and dry spells – A wet spell is a number of continuous days of rainfall. A dry spell is a number od continuous rainless days.
3. Rainy days: If the rainfall received is more than 2.5 mm on any day. This particular day is called rainy day.
4. Periodicity of rainfall.
5. Onset of monsoon.
6. Recurrence of rainfall events.
7. Dependability of rainfall
8. Certificient of variation. If C.V. is more variation in rainfall is more and vice – a – versa.
9. Length of the growing season (LGS): If LGS is less a short duration crop should be selected. L.G.S. depends on duration of rainy season and moisture retention.
Rainfall being a single most important factor for success of crops in the dry farming areas. It is generally known that India receives its annual rainfall by the particular phenomenon called monsoon which consists of series of cyclones those arise in the Indian Ocean. These travel in the North East direction and enter the peninsular India along the Western coast. These cyclones occur from June to Sept. is known as south West monsoon. This is followed by second third and fourth rainy season during periods from Oct. to Nov., Dec. To Feb. and March to May respectively. South West Monsoon is the most important as it covers major parts of India and brings bulk of the total annual rainfall.
The North East of Returning monsoon: By the end of Sept. South West Monsoon ceases to penetrate North West India but continues a full month longer in Bengal. On account of south East North easterly winds being to flow on the Eastern coast. Some times some of these cyclones penetrate In land and give supplementary rainfall to dry region of the plateau of the peninsular India. This is known as returning monsoon.