RAINFALL VARIABILITYAND TREND IN THE NORTHERN REGION OF SRI LANKA

Abstract

In this study, the rainfall variability and trend of the Northern Region of Sri Lanka (NRSL) isexamined. Long term monthly rainfall data (1881-2015) were obtained for sixrain gauge stations of Jaffna, Mannar, Kanukkeni, Vavuniya, Pavatkulam and Muttayankaddu. To study the inter-annual and decadal variability and trend, Coefficient of Variation (CV), least square trendand Standardized Precipitation Index (SPI) were used as descriptors of rainfall variability. The SPI had computed for 1, 2, and 3 -month time scale for all six rain gauge stations.The mean annual rainfall of NRSL is 1233mm and its CV range is varies spatially from 24.8% to 33.1%. The analysis demonstrates the intensity of flood, drought and normal years. Out of 135 years,40 years were experienced as flood and 20 years as drought. The probability flood year is 0.296 and drought year0.148. The study revealed that the occurrences of flood years are more (30%) than the drought years (15%). The decadal variability and trend of rainfall results revealed that the decreasing trend was prolonged in the decades of 1881-1890, 1901-1910, 1921-30, 1931-40, 1971-80 and 1981-90 and increasing trend noticed in the decades of 1891-1900 and 1951-1960.