Rainfall Trends in the North-Western and Eastern Coastal Lines of Sri Lanka Using Non – Parametric Analysis

The changes in the global rainfall have raised concerns over the present and possible future use of coastal areas in many Asian countries including Sri Lanka. However, no in-depth analysis of rainfall of these coastal lines of Sri Lanka has been performed yet to understand any changes in the pattern in general. This study was carried out to fulfil the above need, especially focusing on rainfall of North-Western and Eastern coastal lines of Sri Lanka. The rainfall data for a period of 30 years (1986–2016) were used in the study and analysis was performed using the tests, Mann Kendall, Sen’s slope estimator, and sequential Mann Kendall. Mann–Kendall’s test indicated positive trend in annual rainfall of most parts of North-Western coastal line but negative monotonic decrease at 4 stations, namely, Chilaw, Horakele, Lunuwila and Palaviya. In the Eastern coastal line, significant positive trend in annual rainfall was observed at 4 stations, namely, Kantale, Batticaloa, Pottuvil and Mylambaveli. The monthly rainfall analysis of North-Western coastal line revealed significant positive trends at Kottukachchiya and Anamaduwa stations in March and December respectively and in the Eastern costal line, positive trends were observed at Kantalae, Mylambaveli and Navatkiri Aru for February. The stations except Anamaduwa in NorthWestern coastal line recorded a significant negative trend in rainfall in the month of May. No station showed a significant positive trend during Southwest Monsoon season. During the Northeast Monsoon season, all the nineteen stations showed an increase in rainfall amounts while two locations in NorthWestern region and six locations in Eastern showed a significant upward trend.  With these dynamic rainfall trends, it can be reiterated that it is vital to advocate climate mitigating actions to reduce impacts of changes in rainfall trends.