Abstract:
Rainfall extremes have adverse impacts on the society and environment of Sri Lanka. Different
regions of the country have witnessed either flooding or drought in quick succession in recent years.
Some studies attribute such extreme events to climate changed induced by global warming. However,
there is a dearth of climatological studies addressing the spatio-temporal trends in rainfall over Sri
Lanka in support of such attribution. Using daily rainfall data collected at the 22 main meteorological
stations of the Department of Meteorology, this paper identifies spatio-temporal trends in the rainfall
received during the four rainy seasons – i.e. the Southwest monsoon, the first inter-monsoon, the
Northeast monsoon and the second inter-monsoon during the period 1961-2002. It translates rainfall
trends into trends in water volume by river basin using different GIS techniques, so that the practical
implications of climate variability and change in recent decades are clearly identifiable. The study
finds that the number of rainy days has decreased at all the meteorological stations except for the
Nuwara Eliya station. It also finds that the 2000mm isohyet – demarcating the wet zone of the
country - has shrunk. Water volume by watershed shows a clear dichotomous distribution with
watersheds in the north having increasing trends, and watersheds in the south having decreasing
trends, in water volume.
