Temporal Rainfall Trends in the Northern and Eastern Coastal Regions of Sri Lanka: An Analysis Spanning from 1981 to 2019

The annual and seasonal rainfall trends and patterns along the Northern and Eastern coastal belt of Sri Lanka were analyzed by studying the daily rainfall records from 1981 to 2019 from five locations: Jaffna, Kanukkerny Tank, Trincomalee, Batticaloa, and Pottuvil, because no such pattern has been addressed previously. The Mann-Kendall test and Sen’s slope estimator were used to detect the annual and seasonal rainfall trends and the magnitude of the trend, respectively. The findings indicate that the eastern coastal belt exhibits more consistent rainfall patterns both annually and seasonally. The rainfall pattern of Jaffna, situated in the Northern coastal region, differs from the aforementioned locations. The long-term mean annual rainfall of all locations was less than 1750 mm. The lowest seasonal rainfall occurs during the first inter-monsoon (FIM) season, amounting to less than 200 mm. During the second inter-monsoon (SIM) season, the entire area experiences its peak monthly rainfall, reaching up to 280 mm/month. The Northeast monsoon (NEM) is distinctly wet season for the entire Northern and Eastern coastal belt, with rainfall surpassing 100 mm/month. Trend investigations reveal that only the Batticaloa has a significantly increasing trend of 17.5 mm/year. This annual significant (p <0.05) trend primarily stems from the noteworthy trend during the SIM, with an increase of 7.3 mm/season. Although converse trends are evident during other seasons across all locations, none of them are statistically significant (p >0.05). In conclusion, the eastern coastal belt demonstrates a more consistent rainfall pattern both annually and seasonally, whereas the rainfall pattern of the northern region differs from it. Furthermore, only the Batticaloa region shows a statistically significant trend with an increment of 17.5 mm/year.