Abstract
Climate change is one of the most-discussed issues in current global fora. The objective of this paper is to seek evidence for climate change in Sri Lanka by analyzing long-term (i.e. from 1869 to 2007) monthly data of air temperature and rainfall from seven selected locations (i.e. Anuradhapura, Kurunegala, Kandy, Ratnapura, Badulla, Nuwara Eliya and Colombo) representing the major climatic zones of the country. Decadal mean air temperatures of all selected locations, except Kandy, showed highly significant (p<0.001) linear increasing trends over the entire 140-year period considered. In all locations, including Kandy, almost continuous decadal warming has occurred during the last 6-10 decades. The rates of continuous warming in all locations except Ratnapura exceeded, by a substantial margin, the global mean (i.e. 0.074 oC decade-1) during the period from 1906 to 2005. Analysis of frequency distributions of annual mean air temperatures showed that the above increases have occurred because of a shift in the entire distribution of temperatures over time rather than due to a few extremely warm years. Four out of the seven locations (i.e. Anuradhapura, Kandy, Badulla and Nuwara Eliya) examined showed statistically significant (p<0.05) linear declining trends of decadal mean annual rainfall (RFa) with time over the whole 140-year period. The highest rate of rainfall decline was shown in Nuwara Eliya at 52 mm decade-1. Within the respective trends over the 140-year period, a period of significant (p<0.05) decline of decadal mean RFa could be identified in all locations except Colombo. In particular, Kurunegala has shown a rainfall decline of 121 mm decade-1 from the 1970s onwards. Kandy and Nuwara Eliya have also shown rainfall declines in the range of 64-67 mm decade-1 since 1940s and 1920s respectively. In all locations, mean RFa during the period from 1990 to 2007 was lower than that during the 1950-1989 period. The reductions ranged from 28 mm yr -1 at Ratnapura to 202 mm yr -1 at Kurunegala. Analysis of shifts in rainfall distributions show that rainfall reductions in the years of extremely lower and higher rainfall have contributed relatively more to the mean rainfall reductions in successive periods than rainfall reductions in the years of average rainfall. In all locations, RFa showed decreasing trends, of varying strengths, with increasing mean annual temperature, Ta, with Nuwara Eliya showing the highest rate of rainfall decline (371 mm oC-1). Analysis of monthly and annual rainfall data from 1950 to 1989 showed that the El Niño phenomenon reduced RFa during the following year in all locations, mainly because of rainfall reductions in June-July (South-West Monsoon) and January-February. From 1990 onwards, these post-El Niño RFa reductions have increased in all locations except Colombo and Ratnapura, where post-El Niño RFa has been higher than in normal years. Notably, in all locations, post-El Niño reductions of June-July rainfall have been absent since 1990, where RFa reductions have occurred because of reductions in January February and October-December (North-East Monsoon) rainfall.