Abstract:
The average temperature decrease (6.5°C km-1
) with increasing elevation in the free
atmosphere is generally called as Environmental Lapse Rate (ELR). The Temperature
Lapse Rate (TLR) along the mountain slopes significantly differs from the free
atmosphere ELR. The TLR along a mountain slope is here termed as the Slope
Environmental Lapse Rate (SELR). The main objective of this study was to identify the
variation of the SELR in the Western and Eastern slopes of the Central Highland in Sri
Lanka during the South-West Monsoon and North-East Monsoon seasons. The seasonal
average temperature has been calculated from 2008 to 2017 from three Meteorological
stations; Nuwaraeliya (1895 m), Ratnapura-Western slope station (34 m), and BadullaEastern slope station (670 m). Elevation and temperature of the Nuwaraeliya were taken
as the base location and calculated the SELR by ((T1-T2)/(H2-H1) *1000) for Ratnapura
and Badulla. The result revealed that the SELR is 5.9°C km-1
in the Western slope and
6.5°C km-1
in the Eastern slope of the Central Highland during the South-West monsoon
season. The Western side of Central Highland receives more rainfall than the Eastern side
when South-West monsoon occurs. During this season the entire area of Eastern slope in
the Central Highland gets dry due to the inverse direction of the monsoon with the effect
of orography rainfall. During the North-East monsoon season, the SELR is 6.4°C km-1
in
the Western slope and 4.9°C km-1
in the Eastern slope due to the stimulating of NorthEast monsoon on the Eastern side. Considerable spatial differences have been noticed
during two seasons. The seasonal monsoon rainfall patterns are highly affected for
variation of the Slope Environmental Lapse Rate in the Western and Eastern slopes of the
Central Highland in Sri Lanka.
.
Keywords: Central Highland, Eastern slope, Seasons, Slope Environmental Lapse Rate,
Western Slope
