WET AND DRY SPELL ANALYSIS FOR AGRICULTURAL CROP PLANNING USING MARKOV CHAIN PROBABILITY MODEL AT BHAVANISAGAR

Abstract

Sequence of dry and wet periods along with onset and withdrawal of rainy season is necessary for successful agricultural crop planning and soil and water conservation measures. In the present study, Markov chain probability model to calculate the chances of occurrences of dry and wet spells was applied for Bhavanisagar using 47 years (1969 to 2015) weekly rainfall. The average annual rainfall of Bhavanisagar was found to be 677.9 mm and coefficient of variation (CV) was 28.4% which is higher than threshold limit that indicates the erratic distribution of rainfall. Monsoon starts on the 24th standard meteorological week (SMW) (11 – 17th June) and remains active up to 46th SMW (12-18th November) with a total length of 22 weeks (154 days). Initial, conditional and consecutive dry and wet week probabilities showed that chances of occurrence of a week getting dry is high during early part of the season and chances of occurrence of a week getting wet is high from 34th week onwards upto 47th week. Chances of occurrence of wet week of more than 30% at the beginning of Kharif season indicates that summer ploughing and initial seed bed preparations shall be taken up in the 20th – 22nd SMW (14th May - 3rd June) and sowing operations can be taken up since 23rd SMW (4th – 10th June). However higher values of CV showed that higher variability of rainfall during this period which questioned the success of growing of rainfed crops. During the rabi season, from 37th week to 49th week high chances of occurrence of wet week of more than 50%, high consecutive wet weeks and the values of CV less than threshold limit of 150 indicates that all agricultural operations like planting/sowing under rainfed condition can be undertaken successfully during this period. Chances of occurrence of consecutive dry weeks indicate the need of supplemental irrigations and moisture conservation. Weekly rainfall of more than 40 mm during 42nd – 45th SMW and chances of occurring consecutive wet weeks during 38th – 47th SMW intimate the potential scope of harvesting excess runoff water for future supplemental irrigations.