According to the Planning Commission Classification, the State as demarcated now falls in middle-Gangetic Plains region. ICAR's agro-ecological division puts it under the sub-humid ecosystem. Based on more desagregated classification, the state is divided into three agro-climatic sub-zones. These are north-west Gangetic plains (Zone I), north-east Gangetic Plains (Zone II) and the South-Bihar Plains (Zone-III).
Bihar is spread over 9.40 million ha of land. The three zones mentioned above constitute about 35, 21 and 44 per cent of total geographical area of the state respectively. Bihar, on the whole, is endowed with congenial climatic conditions for cultivation of wide range of crops and trees.
The three zones have little variation in climate having hot summer, wet monsoon and dry winter with temperature reaching above 45ºC in June. The minimum temperature reaches below 5ºC in January.
Jehanabad district fall in agro-climatic Sub-Zone III. The average annual rainfall in the Jehanabad district is 1313 mm (Fig. 1). This is just sufficient for the type of agriculture practiced traditionally in this district. But year to year variation make short fall from normal very common. In fact, the variability of rainfall leading to difficulty of agriculture during monsoon season is very frequent in the drier zone of the district. In addition, it must be remembered that the time to rainfall is also important. The timely rainfall is very crucial for the type of agriculture being practised in the district and it gives a boost to increase the production.