Seasonality and Periodicity of Trends in Rainfall and Temperature in Sri Lanka

Abstract

Climatic changes are an important factor especially in view of current global warming scenarios. Study of climatic changes in Sri Lanka is reievant, particularly, as any change in the seasonality of rainfall can affect the country's agricuitural productivity. Henee, the present study attempts to separately ascertain whether there have been changes in seasonal rainfall and temperature in the ‘dry’ and ‘wet’ zones during the 1870-1999 period. As there are no cyclic changes or linear trends observed for the whole study period, the period was divided into four sub-periods: 1870-1909,1910-1939, 1940-1969 and 1970- 1999. Simple regression coefficients were calculated for those sub-periods. Rainfall and temperature were calculated by spatial averaging. Measurement errors and fluctuations were reduced by averaging the data from different locations. As monthly data do not necessarily relate to seasonality, only typical months for each of the four seasons were selected and the data were averaged for the respective seasons. The analyses reveal the following trends: a decrease of rainfall of both monsoon seasons and an increase of rainfall of the two inter-monsoon seasons when whole study period is considered. As for temperature, there has been a slight increase all over the island (with the exception of a slight decrease in the dry zone in the 1910-1939 period ). The trends were also calculated for four periods.