Spatial and temporal variation of rainfall trends of Sri Lanka

Abstract

This study was based on daily rainfall data of 48 stations distributed over the entire island covering a 30-year period from 1981 to 2010. Data analysis was done to identify the spatial pattern of rainfall trends. The methods employed in data analysis are linear regression and interpolation by Universal Kriging and Radial Basis function. The slope of linear regression curves of 48 stations was used in interpolation. The regression coefficients show spatially and seasonally variable positive and negative trends of annual and seasonal rainfall. About half of the mean annual pentad series show negative trends, while the rest shows positive trends. By contrast, the rainfall trends of the Southwest Monsoon (SWM) season are predominantly negative throughout the country. The first phase of the Northeast Monsoon (NEM1) displays downward trends everywhere, with the exception of the Southeastern coastal area. The strongest negative trends were found in the Northeast and in the Central Highlands. The second phase (NEM2) is mostly positive, except in the Northeast. The Inter-Monsoon (IM) periods have predominantly upward trends almost everywhere, but still the trends in some parts of the Highlands and Northeast are negative. The long-term data at Watawala Nuwara Eliya and Sandringham show a consistent decline in the rainfall over the last 100 years, particularly during the SWM. There seems to be a faster decline in the rainfall in the last 3 decades. These trends are consistent with the observations in India. It is generally accepted that there has been changes in the circulation pattern. Weakening of the SWM circulation parameters caused by global warming appears to be the main causes of recent changes. Effect of the Asian Brown Cloud may also play a role in these changes.

Monitoring Water Resources over the Kotmale Reservoir in Sri Lanka Using ENSO Phases

“…Insignificant decreasing rainfall trend is observed in Labukelle-estate station. However, Chandrasekara and Prasanna [29] and Wickramagamage [32] showed that there are predominant negative trends in the annual rainfall of central highlands including the study stations. Therefore, increase in rainfall in the JJAS season has low influence on the annual rainfall of the selected stations.…”

Impact of climate variability on hydropower generation in an un-gauged catchment: Erathna run-of-the-river hydropower plant, Sri Lanka

“…However, they found that the intensity of rainfall was increasing. In addition, Ranatunge et al (2003), Jayawardene et al (2005), Wickramagamage (2016) and Karunathilaka et al (2017) have put efforts in studying annual and seasonal rainfall trends in Sri Lanka. (Khaniya et al 2018) presented some interesting rainfall trend analyses and linked them with the hydropower generation of a ROR hydropower plant.…”

Managing Water and Soils to Achieve Adaptation and Reduce Methane Emissions and Arsenic Contamination in Asian Rice Production

“…Farmers rely largely on inter-monsoonal and monsoon rains, thus placing them at substantial risk of crop failure in years when rainfall is limited or delayed [61]. Several authors have shown that rainfall in Sri Lanka declined during the latter half of the 20th century [62][63][64]. Domroes and Schaefer [65] suggest that the estimated average annual rainfall declined from 2005 mm during 1931 to 1960, to 1861 mm (7.2%) during 1961 to 1990.…”