Variations in rainfall patterns of Batticaloa (DL2b) in terms of severity and frequency of occurrence of wet and dry events

Abstract

Variations in climatic patterns are known to influence the availability and sustainability of water resources in Sri Lanka, thereby influencing the agriculture based livelihoods and economy. Hence, due attention is required to be paid on the variations of climate patterns, while focusing on the changes in rainfall patterns that directly denote the changes in climate. Standardized Precipitation Index (SPI) remains as one of the widely used approaches in evaluation and prediction of variations in rainfall patterns, due to its simplicity and effectiveness. Periodic variations of such climate extremes in Batticaloa (DL2b agroecological zone) were studied, to evaluate the trends and severity of climate extremes using the Standardized Precipitation Index (SPI). Monthly cumulative rainfall data from January, 1900 to December, 2014 of the Batticaloa rain gauging station were used in this study. The collected monthly accumulated rainfalls were arranged into two major time periods, ranging from 1900-1956 (past years) and 1957-2014 (recent years) to be used as the input to the SPI calculation in Mat Lab R2007b (version 7.5). The identified events (both wet and dry) were ranked into five classes based on the magnitude (severity) of each event as normal, mild, moderate, severe and extreme. The variations in rainfall patterns (with respect to SPI) were evaluated by using the Paired Chi-Square test. The dry events of Batticaloa in the recent years (1957-2014) indicate a significant reduction of the severity of drought events (p<0.05 at 95% level of confidence), as the occurrence frequency of extreme and severe droughts decrease with increments in mild and moderate drought events. On the other hand wet events indicate notable increments in mild, moderate, severe and extreme wet events within the recent years, which is not significant in terms of Paired Chi-square statistics (p>0.05). Hence, a significant reduction of the dryness along with a notable increment in wetness, in terms of severity and frequency of occurrence, could be predicted for Batticaloa, in accordance with results of SPI.