Abstract:
The study was conducted to identify the relationship between current rainfall pattern
and paddy cultivation in Sri Lanka with relation to time periods of Yala, Maha onset and
Maha harvesting. The analysis was carried out using rainfall data for 33 years (1976-
2008) and Pan evaporation data at different agro-meteorology and meteorology stations,
namely Jaffna, Anuradhapura, Ampara, Angunukola Pelessa, Lunuwila, Monaragala,
Colombo, Ratnapura, Badulla, Matale, Bandarawela and Sitaeliya. Histogram analysis of
mean weekly rainfall for four durations was used to identify the onset for Yala and Maha.
Probability plot analysis was applied to ensure the accuracy in addition to the standard
deviation values. Moreover, Hargreaves Moisture Availability Index (MAI) at 75 percent,
70 percent, 65 percent, and 60 percent probability rainfall was used to identify the onset
for both seasons.
Literature reveals that the rainfall onset for Yala and Maha seasons are 13th and 40th
weeks respectively. Based on Histogram analysis, rainfall onset occurred at 13th -14th
week for Yala and 38th -42nd week for Maha. Onset for both seasons in some stations was
not identified using this methodology.
Based on Hargreaves MAI method, dependable rainfall at 75 percent probability level
noted, no onset for Yala was identified in Monaragala. When probability level of
dependable rainfall was reduced, onset for Yala was varied between 13th -15th week. Most
stations, rainfall onset for Maha was taken place at the 38th-42nd week at 75 percent
probability level. The results indicated that the duration of rainfall in Yala was not
sufficient and rainfall duration in Maha was adequate in most areas for rain-fed paddy
cultivation. Probability level of overlapping of rainfall onset of Yala with harvesting of
paddy in Maha at 8th week was less than 50% in all selected stations. When the dry zone
was concerned it was lower than 35%. Regionalization was done based on the results
obtained by the research and maps were produced accordingly.
