The commencement, termination and length of the major (Maha) growing season over the dry zone of Sri Lanka were determined using daily rainfall records from 1981 to 2019 of ve meteorological stations (Anuradhapura, Polonnaruwa, Hambantota, Puttalam and Batticaloa). Cumulative percentages of daily rainfall were plotted against the time and maximum positive and maximum negative curvatures were derived as the commencement and termination dates of the season. A Gaussian model was tted on the cumulative distribution curve in order to remove limitations in deriving maximum positive and maximum negative curvatures. The difference between commencement and termination dates were taken as the length of the growing season. Results disclosed that there is a considerable inter-annual variation of commencement and termination dates and the length of the Maha season. Mean commencement and termination dates fall in the standard week 44.04±2.61 (end of October) and 5.10±4.20 (1st week of February). The average seasonal length is 13.7±4.24 weeks. Terminating date acts as the key determinant of the seasonal length. Any signi cant (p > 0.05) trend could not be observed for commencement, termination and length of the season for the analyzed period in any of the locations. It can be concluded that cumulative distribution of rainy days can be successfully used to determine commencement and termination dates of the Maha season over the dry zone of Sri Lanka where a single peak rainy period is available. However, the method needs modi cations, when it applies in wet zone of the country where bimodal rainfall pattern is prominent.dates for the season so that further modi cations are required to smooth the process. Further, the method could be tested in the wet zone of the country where bimodal rainfall pattern is prominent with suitable modi cations.
Declarations