A Study on the Trends of Rainfall Patterns in the Intermediate and Dry Zones of Sri Lanka A Comparative Study for the Periods Ranging from 1941-1970 and 1971-2000

L. M. Wickramanayake, E. M. S. Ranasinghe

Abstract


Since Sri Lanka is a tropical island unstable nature of the tropics has madeseveral temporal and spatial variations in rainfall throughout the island. Rainfall is oneof the principal factors that has been used to identify the three broad climatic zones inSri Lanka, namely the Wet zone, Intermediate zone and Dry zone. Much of thescientific researches on the rainfall pattern in Sri Lanka have revealed that most of themeteorological stations had recorded decreasing trends of rainfall during the past 100years. The present study attempts to ascertain the validity of these findings withreference to the study area of Intermediate and Dry zones of Sri Lanka (hereafterreferred to as the Intermediate and Dry zones). Considering the agricultural economy,the Dry and the Intermediate zones have been contributing towards more than 90% ofthe islands paddy. However, these two climatic zones show water surpluses in onlythree months (October to December) of the year. With this brief background, the presentstudy aims to identify the trends in rainfall in the Intermediate and the Dry Zones.

Micro level framework is used for the selection of rainfall reporting stations andagro-ecological regions of these two zones. Accordigly 14 rainfall reporting stationshave selected for the study. Further, this is a comparative study of two 30 year periodsranging from 1941-1970 (1st period) and 1971-2000 (2nd period) and its seasons (FirstInter Monsoon (FIM), South West Monsoon (SEM), Second Inter Monsoon (SIM) andNorth East Monsoon (NEM). Time series analysis is employed for the identification ofany positive or negative trends of rainfall and the analysis is done on annual andseasonal basis.

The results obtained from the analysis revealed that the highest and the lowestpositive trends belong to the 2nd period. It is clear that both highest and lowest negativetrends are apparent in the 1st period. All positive trends of the FIM in the 1st period havechanged into negative trends in the 2nd period. During the SWM, the highest positivetrend is showed in the 2nd period.

Keywords: Rainfall Pattern, Intermediate Zone, Dry Zone, Positive Trend, NegativeTrend


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