Abstract:
Sri Lanka is an island in the Indian Ocean, located off the southern coast of India. The
climate of Sri Lanka is considered to be warm and tropical. The mean daily temperature
ranges from about 16 °C in the central highlands, to a maximum of 33 °C in low-altitude
coastal areas. There are predominantly two climatic zones in Sri Lanka, the central and the
south-western part of the country, known as the wet zone and the southeast, east, and
northern parts of the country, known as the dry zone. When considering the wind pattern,
the year can be divided into four climate seasons, namely the two monsoons (South-West
from May to September and North-East from December to February) and the two inter
monsoons. There is high variability of rainfall in different parts of the country during
these four seasons. Since Sri Lanka’s economy depends on agriculture production,
understanding temporal variation in climate in different parts of the country, especially the
variations in the start and end of the rainy seasons is important to enhance agricultural
productivity.
A number of methods have been adopted to determine the onset and retreat of rainy
seasons (Odekunle, 2006). Studies carried out in Africa show that the percentage
cumulative mean rainfall is one of the frequently used methods. Since rainfall is a readily
available measurement, there are advantages in using it rather than using an associated
variable. Since patterns of dry spells and wet spells at the start and end of rainy seasons
are critical for crop growth, there is an advantage of developing an index to determine the
start and end of rainy seasons based on the temporal patterns of rainfall events (Cook,
G.D., Heerdegen R.G. 2001). The main objective of this study is to look into the
feasibility of determining the onset and the retreat dates of the rainy season in the dry
zone.
