Probability analysis of rainfall at Kohima (Nagaland) for crop planning

In the present study daily rainfall data (1997 to 2004) collected for Kohima, Nagaland were converted into weekly, monthly, seasonal and annual series. The average annual rainfall and the average annual rainy days were 1660.8 mm and 116.2, respectively for Kohima. The mean seasonal rainfall of pre-monsoon (March to May), monsoon (June to October) and post monsoon (November to December and January to February) period was observed to be 319.8 mm, 1280.5 mm and 60.5 mm with mean number of rainy days with 28.2, 82.3, and 5.7, respectively. During monsoon, pre-monsoon and post-monsoon seasons 77.1%, 19.25% and 3.65% of the mean annual rainfall occurred respectively. During the post-monsoon season occurrence of rain is less and predominately dry requiring supplementary irrigation. For forecasting the weekly rainfall, Normal, Lognormal, Gamma, Log-Pearson Type III, and Extreme Value Type I probability distribution functions were fitted. Forecasting of weekly rainfall was carried out at 10 to 90% probability levels. Weekly forecasting of rainfall indicated that expected rainfall is scarce from the month of November to February at all probability levels. At 70% or above probability level there is less rainfall from week numbers 41^th to 52^th and 1^st to 19^th indicating that crop production will require artificial supplementing of water through irrigation.