Severity and Frequency of Occurrence of Wet and Dry Events in the IL1a Intermediate Zone of Sri Lanka

Abstract

The changes in the climate patternshave caused significant impacts on the socioeconomicparameters. Sri Lanka, as an agricultural country, has to pay more attention to extremes andalterations of climate patterns for the sustainable planning and management of waterresources to facilitate agriculture.Thus, the analysis of the shifts and trends of the climatepatterns with respect to severity and the frequency of occurrence of wet and dry eventsis vitalfor a proper and sustainable planning and management of water resources.Hence, periodicvariations of such climate extremes in a locality of intermediate zone (Rathmalagara in theIL1azone) was studied to evaluate the trends and severity of climate extremes using theStandardized Precipitation Index (SPI) which has proven to be useful in evaluation andprediction of such events due to its simplicity and effectiveness. Daily rainfall data for fiftyyears (1961 to 2011) from the Rathmalagara rain gauging station located within the IL1aagroecologicalzone was used in this study. Monthly accumulated rainfalls for each month of theconsidered periods (1961-1985 and 1986-2011) were used as the input to the SPI calculationand the variation of rainfall depth and SPI in both the intervals were plotted with respect totime.The events were ranked into five classes based on the severity of each events and theoccurrence percentage of each wet and dry event was calculated. The climate events in therecent year period of 1986-2011 indicated only a slight reduction in both dry events (1.52%,0.76%, 1.52% reduction in normal dry events, moderate droughtsand severe droughts) andwet events (4.29%, 0.71% and 0.71% decreaseinnormal wet, severe wet and exceptionallywet events) when compared to the significant climate events of the past (from 1961 to 1985).Thus the results suggest a hindering in the occurrence of climate extreme events at presentwhen compared to the significant climate extremes recorded in the past. Hence, a moreuniform climate pattern with less severe extreme events (both wet and dry) in terms of bothseverity and frequency of occurrence could be predicted for IL1a zone, in accordance withSPI.