Rainfall in Sri Lanka
Annual 2540 mm to over 5080 mm in south
west of the Island. Less than 1250 mm in the north west and
south east of the Inland.
· South West Monsoon- May to
· North East Monsoon- November to February
Agriculture in the north and east suffers
badly during the South-west Monsoon because the moisture bearing
winds dry out as they descend over the Central Highlands,
producing hot, during and often very strong winds. Thus June,
July and August are almost totally rainless throughout the
Dry Zone. For much of the time a strong, hot wind, called
yalhulanga by the Sinhalese peasantry and kachchan by the
Tamils, desiccates the land.
Nearby three quarters of Sri Lanka lies
in what is widely known as the 'Dry Zone', comprising the northern
half and the whole of the east of the country. Average annual rainfall
in this region is generally between 1,200-1,800 mm. In comparison
with many parts of Europe this may not seem unduly dry, but like
much of SE India, virtually all of the region's rain falls in the
3 months of the north-east Monsoon between October and December.
The rain often comes in relativity short but dramatic bursts. Habarana,
for example, located in the Dry Zone between Polonnarywa and Anuradhapura
received 1,240 mm (nearly 50") of rain in the 3 days around
Christmas in 1975. These rains caused catastrophic floods right
across the Dry Zone.
The Wet Zone also receives some rain during
this period, although the coastal regions of the South-west are
in the rain shadow of the Central Highlands, and are much drier
than the North-east between November and January. The South-west
corner of Sri Lanka, the Wet Zone, has its main wet season from
May to September, when the South-west Monsoon sweeps across the
Arabian Sea like a massive wall of warm moist air, often over 10,000m
thick. The higher slopes of the Central Highlands receive as much
as 4,000 mm during this period, while even the coastal lowlands
receive over 500mm.
From the October to December cyclonic storms often from over the
Bay of Bengal, sometimes causing havoc from the southern coast of
India northwards to Bangladesh. Sri Lanka is far enough south to
miss many of the worst of these, but it occasionally suffers major
cyclones. These generally come later in the season in December and
January and can cause enormous damage and loss of life.