ABSTRACT
The primary objectives of the study are to examine the rainfall variability in the last 140 years from 1881 to 2020 and to analyze the frequency of drought and its severity. The long-term monthly rainfall data have been obtained from the Department of Meteorology from 1881-2020 for 28 stations in Sri Lanka and used. Other relevant information had collected from various government departments to study these objectives. To analyze the rainfall variability and trend mean, standard deviation, coefficient of variation, and time series analysis had used. To study the drought Standardized Precipitation Index (SPI) has been applied. The rainfall variability results reveal a coefficient of variation of the annual rainfall of Sri Lanka is 21.7%. However, it varies spatially from 15 to 27%. The rainfall variability is higher in the dry zone (23.8%) than in the wet zone (18.6 %). The long-term rainfall for the Dry zone and Wet zone of Sri Lanka shows a decreasing tendency. The SPI-based drought analysis for the Dry zone of Sri Lanka reveals that out of 140 years of study periods of 32 years had experienced droughts. The probability of drought is P = 0.229; once in four (04) years a drought could be expected in the dry zone. Besides, 1974, 1980 and 2016 had experienced extreme droughts. In 1950, 1968, and 1983 were severe droughts. The drought scenario of the wet zone of Sri Lanka reveals that out of 140 years, 25 years had experienced drought, and the probability of the occurrence is P=0.164. Three extreme droughts occurred in 1980, 1983, and 2016, and four severe droughts had observed in 1890, 1950, 1974, 1976, and 2001. The frequency of drought occurrence is higher in the epochs of 1991-2020 (36%) and 1961-1990 (32%).
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