Trends in extreme rainfall events in Sri Lanka, 1961 - 2010

Many parts of Sri Lanka are vulnerable to extreme rainfall events leading to floods and droughts. This study was focused on a trend analysis of climate extremes derived from daily rainfall records. The daily rainfall data from 13 meteorological stations representing different geographical regions in Sri Lanka for the period 1961–2010 were chosen. The analysis was carried out separately for summer half year (March-August) and winter half year (September-February) to capture the possible changes in two growing seasons, Yala and Maha. Magnitudes of trends were derived using linear regression analysis while the statistical significance was determined using the Mann-Kendall test. Spatial maps were used to study the regional differences in climate extremes. Extreme rainfall events were found to be isolated events without coherent increasing or decreasing trends. However, statistically significant increasing (decreasing) trends were observed for number of dry days (wet days) ranging from 1.1 to 3.1 days/decade in most parts of the island during the summer half year, except for the coastal areas of the dry zone. No increasing or decreasing trends in extremes were observed for the winter half year. Based on the analysis, it was concluded that there is widespread climate change leading to increasing (decreasing) dry days (wet days) during the summer half year receiving rainfall predominantly from the South-West monsoon. However, mixed results were obtained for the winter half year.