Analysis of Dynamic Trends of Rainfall Extremes in Sri Lanka Using Frequency Indicators

Abstract

Occurrence of rainfall extremes is becoming more frequent in the world incurring a number of issues for livings and non-livings in Sri Lankan context too. It is timely important to identify the trends of frequent rainfall extremes so as to implement better adaptation practices. This study identifies dynamic trends of rainfall extremes from 1981 to 2010 using frequency indicators (Consecutive Wet Days (CWD), Consecutive Dry Days(CDD) , Heavy Rainfall Days (R10mm) and Very Heavy Rainfall Days (R10mm) promoted by the World Meteorological Organization. Daily rainfall data are used to run RClimDex 1.0 to identify the extremes. The extremes are mapped and Non parametric Mann Kendall test is used to detect the trends and their significance. Additionally, this study considers the impact of Southern Oscillation on occurrence of above extremes as one of the causal factors. All the stations show a decreasing trend of CDD where Puttalam, Hambanthota, NuwaraEliya, Rathnapura display significant decreasing trends. Mean CDD in Sri Lanka is 38 days. Lower annual averages of CDD are apparent in 1985, 1991, 2003 and 1981 which are highly coincided with southern oscillation index. Average CWD is 11 days while it ranges from 4 to 37 days. Galle, Katunayaka, Anuradhapura show significant increasing trends in CWD while trends of NuwaraEliya and Rathnapura are significantly decreasing. An average of 53 R10mm are visible whereas Rathnapura records an average of 103 days. Frequencies of R10mm showing an increasing trend in all stations excluding NuwaraEliya where trends are statistically significant in Galle, Kandy, Rathmalana and Trincomalee. An average of 30 R20mm records in the country. Ratnapura is highly vulnerable for R20mm that normally 64 days of very heavy rainfall is visible. But it ranges from 51 to 81 days. Colombo, Rathmalana, Hambanthota, Rathnapura, Badulla, Baticaloa depict significant increasing trends in R20mm. Accordingly most of the extremes are concentrated in to south eastern quarter of the country and

1stIntradisciplinary Conference of Management Researchers Innovation, Integration and Inspiration towards Sustainable Future 10 1100 10th tthh th --12 1122 12th tthh th August 2016 August 2016 August 2016 August 2016 – –– – Sabaragamuwa University of Sri Lanka Sabaragamuwa University of Sri Lanka Sabaragamuwa University of Sri Lanka Sabaragamuwa University of Sri Lanka

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effective adaptation practices should be initiated to cope with the changing trends of climate.