Abstract
The average annual rainfall of Sri Lanka varies from 900 mm to 5,500 mm. A debate and misconception have continued on the “wettest place” or the rain gauge station that receives the highest rainfall in the country. Seven rain-gauge stations (seven locations) were selected considering the regions receiving with probable highest rainfall in Sri Lanka. The average annual total rainfall and average number of rainy days were analysed using daily rainfall data covering the most recent five years (2015 – 2019) to detect the rain gauge station receiving the highest rainfall. Among the locations considered, the newly established rain gauge station at the Welioya Estate (6.9288 N, 80.5582E, 1,258 m amsl) reported the highest rainfall, where the estate has received an average annual rainfall of 5,081 mm. Except during the South West Monsoon (SWM) season (May to September), the three rain-gauge stations located around Watawala Estate have recorded the lowest cumulative seasonal rainfall catch resulting in the same pattern of ranks in the average annual total rainfall. This study revealed that the Welioya Estate in Hatton receives the highest average annual rainfall in Sri Lanka. However, absence of standard rain-gauges installed in many locations in Sri Lanka to collect daily observations is a drawback in conducting detailed analysis rainfall across all agro-ecological regions in Sri Lanka.
Highlights
Despite its relatively small aerial extent, Sri Lanka exemplifies a variety of climatic conditions, especially the rainfall regime depending on the geographical settings of respective locations
All three rain-gauge stations selected from the Watawala area recorded a comparatively lower rainfall during the First Inter-Monsoon (FIM) season along with lower standard deviations (Table 4)
This leads to more FIM rains at lower elevations than mid- and upper-slopes of the Central highlands (Punyawardena, 2008)
Summary
Despite its relatively small aerial extent, Sri Lanka exemplifies a variety of climatic conditions, especially the rainfall regime depending on the geographical settings of respective locations. Rainfall of Sri Lanka is of multiple origins, namely, monsoonal, convectional and weather systems formed in the Bay of Bengal account for major share of the annual rainfall (Punyawardena, 2020). The four rainfall seasons that have been recognized in the rainfall calendar of Sri Lanka are based on the monsoons (Chandrapala, 2007). These are the First Inter-Monsoon (FIM; March-April), South West Monsoon (SWM; May-September), Second InterMonsoon (SIM; October-November) and North East. Rainfall during the SWM period varies from about 100 mm to over 3,000 mm, and the highest rainfall is received in the mid elevations of the western slopes of Central highlands
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