Conditional Probabilities of Excess, Normal and Deficient Southwest and Northeast Monsoon Rainfall of Kerala

The dominant monsoon spells in Kerala are southwest and northeast monsoons during June to September and October to December, respectively. The crop planning in the state varies in accordance with the pattern of these monsoons and their duration. Hence, it is beneficial to assess the influence of monthly rainfall on the rainfall during southwest monsoon and northeast monsoon seasons in order to help better crop and irrigation management. The method of conditional probability was employed in the present study to determine the critical months in corresponding monsoon seasons. Since the cropping pattern varied spatially across Kerala, the study was concentrated in stations representing the five agroclimatic zones of Kerala viz., Pilicode (northern zone), Vellanikkara (central zone), Vellayani (southern zone), Ambalavayal (high range zone) and Kumarakom (problem area zone). Using the seasonal and monthly rainfall data of 37 years from 1983 to 2019 collected from former stations, the probabilities of excess, normal and deficit rainfall was estimated in terms of quartiles, for each season and month in different stations. An attempt was made to estimate the conditional probabilities to decide whether the seasonal rainfall was excess, normal or deficient when monthly rainfall was excess, normal and deficient, respectively. At Vellayani, the exceedance probability is more than 50 per cent for southwest monsoon when rainfall in June was excess. When July or September has excess rainfall at Kumarakom, the season expects excess rainfall with 60 per cent probability. Similarly, excess rainfall in June or July determines excess rainfall in the season at Vellanikkara. When August or September receives excess rainfall, the probability is more for excess rainfall during southwest monsoon, at Pilicode. Ambalavayal experiences excess rainfall with 80 per cent possibility when July has excess rainfall. Similarly, the effect of rainfall in October and November varies over northeast season. Such information from probability analysis can be manipulated to decide when to take prior measures to anticipate the threat of extreme conditions of rainfall.

Pooja A.*1, Laly J. C.2 and Ajithkumar B.3 Click here to download file

Research Article | Published online : 18-Jun-2021