Rainfall Variability in Ratnapura District: A Comparative Study of the Two 30-year Standard Periods of 1961-1990 and 1991-2020

Abstract

Ratnapura district in Sri Lanka could be identified as an area that is constantly affected by the adverse effects of rainfall variability; hence it is important to study the temporal patterns and distribution of rainfall variability in the area during the recent past decades. Therefore, this research aims to compare the annual and seasonal rainfall variability of the Ratnapura district based on the standard 30-year periods of 1961-1990 and 1991-2020. Fundamental statistical methods of coefficient of variation, Precipitation Concentration Index, and Standardised Precipitation Index were used to analyse the data. The study revealed that temporal patterns of rainfall variability in the district showed almost similar situations for both the 30-year periods. Temporal distribution of annual and seasonal rainfall variability also showed almost similar situations for both periods and was remarkable with uniform and moderate concentrations of rainfall variability. Relatively the highest variability of rainfall could be detected during the Northeast monsoon season. Although no differences in occurring extreme wet conditions between the two 30-year periods, it is clear that drier conditions of rainfall have decreased in the second 30-year period. The study also confirmed that no prolonged wet and dry conditions were reported in the Ratnapura district during the considered two 30-year periods.