Sri Lanka’s climate:
Climate is defined as the state of the atmosphere in a certain area over an extended period of time (from one month to many millions of years, but generally 30 years). The total of atmospheric components (and their fluctuations), solar radiation, temperature, humidity, clouds, precipitation (type, frequency, and amount), atmospheric pressure, and wind constitute the climate (speed and direction).
The climate of Sri Lanka might be described as tropical due to its location inside the tropics between 5° 55′ and 9° 51′ North latitude and 79° 42′ to 81° 53′ East longitude.
The geography of Sri Lanka may be split into three peneplains, or erosion levels. The lowest level, which runs from 0 to 30 meters, forms the seashore and a portion of the north-central plains. This encircles a hilly core in the south generated by a second peneplain rising to 480 m and a third higher peneplain rising to 1,800 m. The central highlands block the path of the two monsoons, causing them to rain. The north-east monsoon occurs between October and January and brings rain mostly to the north-east, whereas the south-west monsoon occurs between May and August and brings rain primarily to the south-west. Both monsoons provide rain to parts of the highlands. The highlands’ Peak Wilderness Sanctuary is described as “the most persistently wet stretch of Asia west of Borneo.” The combination of rainfall and topography has resulted in climatic zones that support race-specific animals and birds. The zones are roughly divided into two: the dry zone, which contains the coastal portions of the nation’s north, east, south, and north central regions; and the wet zone, which includes the west and the mountainous central massif.
The wet zone might be further segmented into low, mid, and high elevations. The wet zone is home to much of Sri Lanka’s wildlife. Despite a long tradition of natural history study, many higher animal species, including small mammals, reptiles, and amphibians, remain nameless. When the highland forests of Sri Lanka were destroyed for coffee in the nineteenth century, numerous indigenous species died before science could even describe them.
Rainfall in Sri Lanka is caused by a variety of factors. The yearly rainfall is dominated by monsoonal, convectional, and depressional rain. The average annual rainfall ranges from less than 900mm in the driest areas (south eastern and north western) to more than 5000mm in the wettest areas (western slopes of the central highlands).
The monsoon winds of the Indian Ocean and the Bay of Bengal impact the rainfall pattern, which is distinguished by four seasons. The first occurs from mid-May through October, when southwest breezes bring moisture from the Indian Ocean. When these winds hit the Central Highlands slopes, they dump heavy rainfall on the mountain slopes and the southwestern section of the island. Some windward slopes receive up to 250 cm of rain every month, whereas leeward slopes in the east and northeast receive very little. The second season occurs throughout the inter-monsoonal months of October and November. During this season, squalls are common, and tropical cyclones can bring gloomy skies and rain to the island’s southwest, northeast, and east. Monsoon winds blow from the northeast during the third season, which lasts from December to March, bringing moisture from the Bay of Bengal. During these months, the north eastern slopes of the Alps may get up to 125 cm of rain. From March to mid-May, there is another inter-monsoonal period with light, changeable winds and night time thundershowers.
Humidity is often higher in the southwest and in hilly locations, and it is affected by seasonal rainfall patterns. Daytime humidity in Colombo, for example, is around 70% all year, reaching nearly 90% during the monsoon season in June. Anuradhapura experiences a daily low of 60% during the inter-monsoonal month of March, but a high of 79 percent during the November and December rains. Kandy’s midday humidity normally reaches 70 to 79 percent in the highlands.
The typical annual temperature ranges from 27°C in the coastal lowlands to 16°C in the central highlands at Nuwara Eliya (1900m above mean sea level). This rather uncommon characteristic, which ranges from sunny beaches to rain forest interiors, is a tourist draw.
The first inter-monsoon season (March-April)
The normal weather conditions during this season are hot and unpleasant with thunderstorm-type rain, especially in the afternoon or evening. The rainfall distribution during this period reveals that the whole south-western sector of the hill country received 250 mm of rainfall, with some areas on the south-western slopes getting more than 700 mm (Keragala, 771 mm). The quantity of rainfall varies between 100 and 250 mm in most sections of the island, with the Northern Jaffna Peninsula being the notable exception (Jaffna-78 mm, Elephant Pass-83 mm).
The southwest monsoon season (May-September)
Windy weather during this monsoon cools down the heat of the first inter monsoon season. Southwest monsoon rains occur during all hours of the day and night, sometimes sporadically, mostly in the country’s southwest. During this season, rainfall ranges from roughly 100 mm to over 3000 mm. The mid-elevations of the western slops got the most rainfall (Ginigathhena-3267 mm, Watawala-3252 mm, Norton-3121 mm). Rainfall falls fast from these maximum places to higher elevations, reaching 853 mm in Nuwara-Eliya. The fluctuation towards the southwestern coastal area is slower, with the southwestern coastal belt receiving between 1000 mm and 1600 mm of rain over a five-month period. The northern and South-Eastern areas have the lowest numbers.
The second inter-monsoon season (October-November)
The normal weather during this season is thunderstorm-type rain, especially in the afternoon or evening. However, unlike the first inter-monsoon season, the second inter-monsoon season is characterized by the presence of meteorological systems such as depressions and cyclones in the Bay of Bengal. Under these conditions, the entire country is subjected to severe winds and widespread rain, which can result in floods and landslides. The second inter-monsoon season of October to November has the most uniformly distributed rainfall throughout Sri Lanka. During this season, almost the entire island receives more than 400 mm of rain, with the Southwestern slopes receiving heavier rainfall in the range of 750 mm to 1200 mm. (Yatiyantota’s Weweltalawa Estate recorded 1219 mm)
The cold and dry wind blowing from the Indian landmass will create a relatively cool but dry weather over many places, making the surrounding weather pleasant and comfortable. Cloudless skies bring sunny days and pleasant, cold nights. During this time, the highest rainfall amounts are reported in the north, on the hill country’s eastern slopes, and on the Knuckles/Rangala range’s eastern slopes. During this era, the most rainfall was recorded in Kobonella estate (1281 mm), while the lowest was recorded in the western coastal area around Puttalam (Chilaw-177 mm).
Total rainfall in the North East monsoon