Assessment of the Predictability of Seasonal Rainfall in Ratnapura Using the Southern Oscillation and Its Two Extremes

Abstract

An attempt is made to assess the predictability of seasonal rainfall at Ratnapura, namely, first intermonsoonal convectional rains (FIM), second intermonsoonal convectional rains (SIM), south-west monsoon rains (SWM) and north-east monsoon rains (NEM) by using Southern Oscillation and occurrence of El Niiio and La Nifia events. Seasonal rainfall data of Ratnapura and three monthly averaged Southern Oscillation Index (SOI) values for 118 consecutive years were analysed for lhg con-elation coefficients (CCs). The link between seasonal rainfall with El Nifio or La Niiia events was evaluated using binomial analysis. The association between FIM rains and the SO1 slrows a weak positivc relationship. All the other seasonal rains, SWM, SIM and NEM are negatively related to the SOI. However, these relationships are _ weak and therefore cannot be used for any predictive purposes without wide margins of eilurs. The link of FIM rains (March to April) either with El Nifio or La Nifia events was not clear. Nevertheless, it is apparent that there is a strong tendency for above normal SIM rainfall (October to November) during El Nifio years. If a n 4 Nifio year is immediately followed by a La Nifia year, both the FIM and SIM rains would produce above normal rains. It is interesting to note that the occurrence of "drougl~t" conditions duringthe SWM season, May to September, is remote in a La Nifia year. Significant associations between NEM rains (December to Fehmary) and El Nifio or La Niiia events were not observed.

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

“…This area is highly vulnerable to frequent flooding due to higher rainfall volumes (Eriyagama et al 2010;Karunathilaka et al 2017). Rathnapura district receives a significant rainfall from SW monsoon from May to September (Punyawardena and Cherry 1999). However, district is famous for receiving rainfall throughout the year.…”

El Niño–southern oscillation influences on rice production in Sri Lanka

“…The relationship between ENSO extremes and rainfall in Sri Lanka has been recognized for two decades (Rasmussen and Carpenter, 1983, Ropelewski and Halpert, 1987, 1989Suppiah and Yoshino, 1986;Suppiah 1997Suppiah , 1998Kane, 1998;Sumathipala and Punyadeva, 1998;Punyawardena and Cherry, 1999). A linkage between agricultural production and ENSO has been established in India (Parathasarthy et al, 1988;Gadgil, 1996), Zimbabwe (Cane et al, 1994;Phillips et al, 1998), the southeastern USA (Hansen et al, 1998) and elsewhere.…”

Predictability of Sri Lankan rainfall based on ENSO

“…Previous detailed analyses of ENSO-rainfall relationships for Sri Lanka (Suppiah, 1989(Suppiah, , 1996(Suppiah, , 1997Fernando et al, 1995;Sumathipala and Punyadeva, 1998;Kane, 1998;Punyawardena and Cherry, 1999;Malmgren et al, 2003) were based on seasons defined by wind-directions, which do not match with the agricultural seasons. The seasons in use also ranged from 2 to 5 months, while contemporary seasonal predictions are most developed at a 3-month time scale.…”