Increasing the occurrence of extreme rainfalls due to climate change has become a common feature of the climate in Sri Lanka during the recent past decades. According to the study on national climate change adaptation strategy for Sri Lanka - 2011 to 2016 undertaken by the Environmental Ministry of Sri Lanka, increase in the intensity of rainfall in the wet-zone due to climate change is expected to increase the propensity for flooding of flood prone rivers. River Kalu is the 2nd largest river in Sri Lanka, causing floods along its route from the most upstream major city of Rathnapura to the most downstream city of Kalutara. According to the Disaster Management Center report in 2005, settlers in the river Kalu flood plains are affected by floods that occur almost annually. With this brief background, the present study was aimed to assess the occurrences and trends of flood events in Kalutara and Rathnapura districts and their spatial and temporal distributions considering the period of 1980-2019. Ordinary Least Square Linear regression method has been used to identify the trends of flood events. Both graphs and maps were used to display the results of the analyses and Arc GIS 10.1 software was used to portrait the maps. The results of the study revealed that both districts have shown a continuous increase in the occurrence of flood events both in spatial and temporal dimensions. The frequency of flood events has increased in the decade of 2000-2009 in both districts. In terms of the spatial distribution of the flood events too, the recent past decade has become more marked compared to the remaining three decades. In Kalutara district, all the DS divisions have experienced flood occurrences during the last two decades. The situation in Rathnapura showed that all the DS divisions have experienced of flood occurrences in the most recent decade of 2000-2009. Bulathsinhala DS division in Kalutara district and Rathnapura DS division in Rathnapura district have reported flood events in every decade and represented of having the highest number of flood events among the DS divisions in their respective districts.

climate change

, extreme rainfalls

, frequency

,occurrence of flood events