Climate change and the variability in rainfall pattern in Sri Lanka

Abstract

Global climate is changing mainly due to rapid increase of emission of greenhouse gases through the anthropogenic activities. Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) has documented that the global temperature had increased by about 0.740C during the period 1905 - 2006. It is also indicated that there is a strong possibility of changing climate pattern with the climate change. Recent analysis of temperature data in Sri Lanka shows that temperature has increased ^ by 0.14 degree Celsius per decade during the period 1930-2000. With the increase of temperature extreme climatic conditions related to temperature and precipitation also have been established in Sri Lanka. Extremes of temperature and precipitation are highly impacted on the agriculture, water and energy sectors, because 70% of paddy cultivation areas in Sri Lanka belongs to the dry zone (Annual Rainfall <1750) and about 40% of power demand in Sri Lanka is catering by hydro power. Therefore receiving rainfall in time is important for the Sri Lankan economy This study was mainly focused to find out the variability of rainfall pattern during the last 60 years. About 300 rain gauges data were used to calculate areal average rainfall for different districts using Thesian Polygon method. Behavior of rainfall pattern shows a decreasing trend for all 25 districts in Sri Lanka. Also it shows that the trend is higher in wet zone ( Annual rainfall > 2500mm) than dry zone (Annual rainfall < 1750). Total rainfall was decreased by an average of 9% and it varies between minimum 2 % in Jaffna to the maximum 19% in Kegalle. Though the rainfall pattern has a decreasing trend, the variability of rainfall pattern plays an important role in the different economical sectors as agriculture, water and energy. 1951-1979 and 1980-2008 periods were used to compare the Coefficient of Variability (CV) and it shows that the CV during the period 1980-2008 has been increased than the period of 1951-1979. Coefficient of variability was compared for the agricultural seasons, Yala and Maha. CV is very much high in Maha season especially in the dry zone. Also the CV is high in dry zone in Yala season, but it not so high during in the wet zone.