Influence of El Nino/La Nina Episodes on the Rainfall Regime of the Dl Region of the North Central Province of Sri Lanka

Abstract

In view of the significance in terms of agricultural production and its dependency on rainfall, the DL, region of the North Central Province (NCP) was chosen to study the influence of El NifiolLa Nifia episodes on the rainfall regime. The rainfall data of two representative stations as mean seasonal rainfall and mean number of rainy days were analyzed based on four seasons i.e. First Inter-Monsoon (FIM), South West Monsoon (SWM), Second Inter-Monsoon (SIM) and North East Monsoon (NEM). Seasonal time series of rainfall data from 1906 to 2000 were divided into El Niiio, La Nifia and Neutral years. Student t-test and chi-square test were carried out to determine whether there were significant differences among the mean seasonal rainfall and mean number ofrainy days in the time series. Both rainfall amounts and the number ofrainy days in SIM seasons showed a statistically significant increase with respect to the situation in Neutral years. Even though i t is not statistically significant, a n apparent increase of mean seasonal rainfall and t h e mean number of rainy days i n NEM seasons have also been evident during El Nifio years. Thus, El Nifio years are likely to produce above normal or a t least near normal rains during the Maha season in the NCP. Hence, appearance and progression of El Nifio type circulation i n the Pacific ocean could be safely used as a long-range forecasting tool for rainfall of the Maha season in the NCP. Although there were obvious differences of seasonal time series of FIM, SIM and NEM between La Nifia and Neutral years, statistically significant relationships could not be established. However, the teleconnection between seasonal rainfall during SWM period and La Niria events was positive a t both locations. This study reveals that there is a n influence of El Niiio and La Nifia episodes on the seasonal rainfall regime of DL, region of the NCP.

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Effects of Climate Change on Urban Rainwater Harvesting in Colombo City, Sri Lanka

“…This further emphases the importance of RWH systems as a supportive water source during dry periods. The rainfall climate of Sri Lanka is characterized by a bimodal distribution with peaks around May and September due to the passage of the inter-tropical convergence zone over the area during these times of the year [27]. In addition, the monsoonal influences and cyclonic storms from the Bay of Bengal contribute to high rainfall from October to December (Figure 3).…”

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