NATURAL RESOURCES OF SRI LANKA

country daily temperature ranges are more significant
than the seasonal change.
Unlike conditions in mid-latitudes of the globe,
seasons in Sri Lanka bring almost unnoticeable temperature
fluctuations. Seasonality primarily results from
variations in the rainfall rhythm, but because Sri Lanka
is a predominantly agricultural country rainfall distribution
over time and space is of great concern.
Climatologjsts divide Sri Lanka's climatic year into
five seasons:
» The convectional-convergence period (March to
mid-April), when the island comes under the influence
of the Inter-Tropical Convergence Zone.
This is a constant daily weather sequence with
bright clear mornings that induce convectional activity
leading to the formation of rain clouds by
early afternoon and thunderstorms in the late afternoon.
» Tliepre-monsoonalperiod (mid-April to late May),
has transitional weather patterns. During this time
convectional weather is gradually suppressed by
surges of the southwest monsoon.
•- The southwest monsoon period(late May to late
September), which brings the largest amount of
rainfall to the southwestern lowlands and
• windward slopes of the central highlands, where
some places receive over 5,000 millimeters annually.
The southwestern monsoon blows across the
northern, north central, and southeastern lowlands
as a dry, desiccating wind.
• Vie convectional cyclonic period (late September
to late November), which begins to appear with the
weakening of the southwest monsoon. Unlike the
convectional weather in March-April, this period
can include cyclones. When combined with convectional
weather, cyclones occasionally produce
periods of heavy rainfall causing widespread floods
and landslides.
• Tlie northeast monsoon (November to February),
has a weak and dry wind compared with that of the
southwest monsoon- However, the northeast mon-
Introduction
soon brings agriculturally significant rainfall to the
northern and eastern parts of the country.
Conventionally Sri Lanka recognizes two distinct
climatic regions - the Wet and Dry Zones — although
precise demarcation is subject to academic debate.
Application of the term "Dry Zone" to an area that
receives over 1,000 millimeters of rainfall can be misleading,
however, and tends to create a psychological
barrier to the human settlement and development of its
resources. In addition some have identified an "Intermediate
Zone" between the 'Wet' and 'Dry* zones,
while others have chosen to depict the coastal areas of
the northwest and those in the southeast as "arid zones."
Hydrology
Sri Lanka's rains feed a radial network of rivers that
begins in the central highlands. Some 103 distinct river
basins cover 59,217 square kilometers. The rest of the
: land is practically devoid of surface water basins of any
significance (Arumugam, 1969). Most identifiable
stream basins are less than 100 square kilometers and
many carry water only during the rainy season.
The chapter on water resources describes the critical
factors that determine how much surface water is
actually or potentially available to Sri Lankans before
it evaporates or reaches the sea, and how much can be
obtained from the ground water recharged by the rains.
Sri Lanka receives about 12 million hectare meters of
water annually from rainfall, of which more than 50
percent is lost through evapotranspiration. Another 20
percent seeps down to replenish ground water. Only
30 percent, or about 35 million hectare meters, is available
as stream flow for irrigation or other purposes.
A substantial proportion of surface water is already
used for irrigation and hydropower generation. The
chapter on inland aquatic systems describes how many
of these uses have already affected the fishing and
wildlife productivity of inland marshes, tanks and other
waters that constitute an unusually high proportion of
Sri Lanka's surface area. Land use in catchment areas
affects the quality of these waters. Sedimentation may
ultimately reduce original estimates of the lifetimes of
dams and irrigation systems. Although water shortages
constrain developments in the Dry Zone, excessive
water flow in the Wet Zone often poses serious prob-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I