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Geography of Cambodia

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Geography of Cambodia

Geography of Cambodia
Continent Asia
Region Southeast Asia
Coordinates
Area Ranked 90th
 • Total 181,035 km2 (69,898 sq mi)
 • Land 97.50%
 • Water 2.50%
Coastline 443 km (275 mi)
Borders 2,530 km (1,572 mi)
Laos 555 km (345 mi)
Thailand 817 km (508 mi)
Vietnam 1,158 km (720 mi)
Highest point Phnom Aural
1,810 m (5,938 ft)
Lowest point Gulf of Thailand
0 m (0 ft)
Longest river Mekong river
486 km (302 mi)
Largest lake Tonlé Sap
16,000 km2 (6,178 sq mi)
Cambodia, Topography

Cambodia is a country in mainland South-east Asia, bordering Thailand, Laos, Vietnam, the Gulf of Thailand and covers a total area of 181,035 km2 (69,898 sq mi). The country is situated in its entirety inside the tropical Indomalayan ecozone[121] and the Indochina Time zone (ICT).[122]

Cambodia's main geographical features are the low lying Central Plain that includes the Tonlé Sap basin, the lower Mekong River flood-plains and the Bassac River plain surrounded by mountain ranges to the north, east, in the south-west and south. The central lowlands extend into Vietnam to the south-east. The south and south-west of the country constitute a 443 km (275 mi) long coast at the Gulf of Thailand, characterized by sizable mangrove marshes, peninsulas, sandy beaches and headlands and bays. Cambodia's territorial waters account for over 50 islands. The highest peak is Phnom Aural, sitting 1,810 metres (5,938 ft) above sea level.[123][124][125]

The landmass is bisected by the Mekong river, which at 486 km (302 mi) is the longest river in Cambodia. After extensive rapids, turbulent sections and cataracts in Laos, the river enters the country at Stung Treng province, is predominantly calm and navigable during the entire year as it widens considerably in the lowlands. The Mekong's waters disperse into the surrounding wetlands of central Cambodia and strongly affect the seasonal nature of the Tonlé Sap lake.[126][127]

Two third of the country's population live in the lowlands, where the rich sediment deposited during the Mekong's annual flooding makes the agricultural lands highly fertile. As deforestation and over-exploitation affected Cambodia only in recent decades, forests, low mountain ranges and local eco-regions still retain much of their natural potential and although still home to the largest areas of contiguous and intact forests in mainland Southeast Asia, multiple serious environmental issues persist and accumulate, which are closely related to rapid population growth, uncontrolled globalization and inconsequent administration.[128][129]

The majority of the country lies within the Tropical savanna climate zone, as the coastal areas in the South and West receive noticeably more and steady rain before and during the wet season. These areas constitute the easternmost fringes of the south-west monsoon, determined to be inside the Tropical monsoon climate. Countrywide there are two seasons of relatively equal length, defined by varying precipitation as temperatures and humidity are generally high and steady throughout the entire year.[130]

Geological development

Cambodia, geological map

Southeast Asia consists of allochthonous continental blocks from Gondwanaland. These include the South China, Indochina, Sibumasu, and West Burma blocks, which amalgamated to form the Southeast Asian continent during the Paleozoic and Mesozoic periods.[131]

The current geological structure of South China and South-East Asia is determined to be the response to the "Indo-sinian" collision in South-East Asia during the Carboniferous.[132] The Indo-Sinian orogeny was followed by extension of the Indo-Chinese block, the formation of rift basins and thermal subsidence during the early Triassic.[133][134][135]

The Indochina continental block, which is separated from the South China Block by the Jinshajiang-Ailaoshan Suture zone, is an amalgamation of the Viet-Lao, Khorat-Kontum, Uttaradit (UTD), and Chiang Mai-West Kachin terranes, all of which are separated by suture zones or ductile shear zones. The Khorat-Kontum terrane, which includes western Laos, Cambodia and southern Vietnam, consists of the Kontum metamorphic complex, Paleozoic shallow marine deposits, upper Permian arc volcanic rocks and Mesozoic terrigenous sedimentary rocks.[136]

The central plains consist mainly of Quaternary sands, loam and clay, as most of the northern mountain regions and the coastal region are largely composed of Cretaceous granite, Triassic stones and Jurassic sandstone formations.[17][137]

General topography

cultivated lowlands in rural Takeo Province at the end of the dry season, May 2010
Borassus flabellifer - sugar palm

Bowl-shaped,[138] Cambodia covers 181,035 km2 (69,898 sq mi) in the south-western part of the Indochinese peninsula as its landmass and marine territory is situated entirely within the tropics.

The bowl's bottom represents Cambodia's interior, about 75 percent, consisting of alluvial flood-plains of the Tonlé Sap basin, the lower Mekong River and the Bassac River plain, whose waters feed the large and almost centrally located wetlands. As humans preferably settle in these fertile and easily accessible central lowlands, major transformations and widespread cultivation through wet-rice agriculture have over the centuries shaped the landscape into distinctive regional cultivated lands.[139][140] Domestic plants, such as sugar palms, Coconut trees and banana groves almost exclusively skirt extensive rice paddies, as natural vegetation is confined to elevated lands and near waterways.[141] The Mekong traverses the north to south-east portions of the country, where the low-lying plains extend into Vietnam and reach the South China Sea at the Mekong Delta region.

Cambodia's low mountain ranges - representing the walls of the bowl - remain as the result of only rather recent substantial infrastructural development and economic exploitation - in particular in remote areas - formidably forested.[142] The country is fringed to the north by the Dangrek Mountains plateau, bordering Thailand and Laos, to the north-east by the Annamite Range, in the south-west by the Cardamom Mountains and in the South by the Elephant Mountains. Highlands to the north-east and to the east merge into the Central Highlands and the Mekong Delta lowlands of Vietnam.[143][144]

A heavily indented coastline at the Gulf of Thailand of 443 km (275 mi) length and 60 offshore islands, that dot the territorial waters and locally merge with tidal mangrove marshes - the environmental basis for a remarkable range of marine and coastal eco-regions.[145]

Soils

low fertile Acrisol

"Sandy materials cover a large proportion of the landscape of Cambodia, on account of the siliceous sedimentary formations that underlie much of the Kingdom. Mesozoic sandstone dominates most of the basement geology in Cambodia and hence has a dominating influence on the properties of upland soils. Arenosols (sandy soils featuring very weak or no soil development) are mapped on only 1.6% of the land area."

"Sandy surface textures are more prevalent than the deep sandy soils that fit the definition for [28]

Geographical extremes

Regions

Central plain

extensive flooding in central Cambodia

The vast alluvial and lacustrine interconnected Cambodian flood-plain is a geologically relatively recent depression where the sediments of the Mekong and its tributaries accumulate as waters are subject to frequent course changes.[147] The area covers 25,069 km2 (9,679 sq mi). The Tonlé Sap lake and - river system occupies the lowest area. The Tonle Sap river is a waterway that branches off the Mekong near Phnom Penh in the north-westerly direction and meets the Tonle Sap lake after around 115 km (71 mi). Its waters' flow reverses direction every year, caused by greatly varying amounts of water carried by the Mekong over the course of a year and the impact of monsoonal rains, that coincides with the river's maximum.[148]

The plains of the Mekong and Tonle Sap basin are confined in the North by the Dangrek and Central Annamite Mountains, and to the South by the Cardamom Mountains and Elephant Mountains. The plains completely surround the Tonle Sap Lake in the western half of the country and wind their way through the middle of the country following the course of the Mekong River. The two basins actually form a single body of water, the whole of which effects about 75% of Cambodia’s land cover.[149]

Flow reversal

Tonle Sap Lake volume over the course of one year

The Mekong river and its tributaries increase water volumes in spring (May) on the northern hemisphere, mainly caused by melting snows. As the Mekong enters Cambodia (over 95% of its waters have already joined the river) it widens and inundates large areas.

The plain's deepest point - the Tonle Sap - flooded area varies from a low of around 2,700 km2 (1,000 sq mi) with a depth of around 1 meter at the end of the dry season (April) to 26,000 km2 (10,000 sq mi) and a depth of up to 9 meters in October/November. This figure rose to 45,000 km2 (17,000 sq mi) during 2000 when some of the worst flood conditions recorded caused over 800 deaths in Cambodia and Vietnam.

Inflow starts in May/June with maximum rates of flow of around 10,000 m3/s by late August and ends in October/November, amplified by precipitation of the annual monsoon. In November the lake reaches its maximum size. The annual monsoon coincides to cease around this time of the year. As the Mekong river begins its minimum around this time of the year and its water level falls deeper than the inundated Tonle Sap lake, Tonle Sap river and surrounding wetlands, waters of the lake's basin now drains via the Tonle Sap river into the Mekong. As a result the Tonle Sap River (length around 115 km/71 mi) flows 6 months a year South-East (Mekong) to North-West (lake) and 6 month a year in the opposite direction. The mean annual reverse flow volume in the Tonle Sap is 30 km3 (7.2 cu mi), or about half of the maximum lake volume. A further 10% is estimated to enter the system by overland flow from the Mekong.[151][34] The Mekong branches off into several arms near Phnom Penh and reaches Vietnamese territory south of Koh Thom and Loek Daek districts of Kandal Province.

Southern Mountains

Tatai River, draining the southern slopes of the Cardamom Mountains
Kampot Province, countryside with remote Elephant Mountains

This region represents the eastern parts of the original extent of the wet evergreen forests that cover the Cardamom - and Elephant Mountains in South-West Cambodia and along the mountains east of Bangkok in Thailand.[152]

The densely wooded hills receive rainfall of 150–200 inches (3,800–5,000 mm) annually on their western slopes (which are subject to the South-West monsoons) but only 40–60 inches (1,020–1,520 mm) on their eastern - rain shadow - slopes.[153]

The Cardamom/Krâvanh Mountains

Occupying Koh Kong Province and Kampong Speu Province, running in a north-western to south-eastern direction and rising to more than 1,500 meters. The highest mountain of Cambodia, Phnom Aural, at 1,810 meters is located in Aoral District in Kampong Speu Province. The Cardamom Mountains form - including the north-western part of Chanthaburi Province, Thailand, the 'Soi Dao Mountains' - the Cardamom Mountains Moist Forests Ecoregion, that is considered to be one of the most species-rich and intact natural habitats in the region. The climate, size inaccessibility and seclusion of the mountains have allowed a rich variety of wildlife to thrive. The Cardamom and Elephant Mountains remain to be fully researched and documented.[154][155][39][156]

The Elephant Mountains

Chuŏr Phnum Dâmrei - A north-south-trending range of high hills, an extension of the Cardamom/Krâvanh Mountains, in south-eastern Cambodia, rising to elevations of between 500 and 1,000 meters. Extending 70 miles (110 km) north from the Gulf of Thailand, they reach a high point in the Bok Koŭ ridge at Mount Bokor (3,547 feet [1,081 m]) near the sea.[157][158][159][160]

To the south-west of the Southern mountain ranges extends a narrow coastal plain that contains the Kampong Saom Bay area and the Sihanoukville peninsula, facing the Gulf of Thailand.

Northern Mountains

Dângrêk Mountains panorama, seen from Cambodia (south)

The Dangrek Mountains

A forested range of hills averaging 1,500–2,000 feet (450–600 m), dividing Thailand from Cambodia, mainly formed of massive sandstone with slate and silt. A few characteristic basalt hills are located on the northern side of the mountain chain. This east–west-trending range extends from the Mekong River westward for approximately 200 miles (320 km), merging with the highland area near San Kamphaeng, Thailand. Essentially the southern escarpment of the sandstone Khorat Plateau of northeastern Thailand, the Dângrêk range slopes gradually northward to the Mun River in Thailand but falls more abruptly in the south to the Cambodian plain. Its highest point is 2,497 feet (761 m). The watershed along the escarpment in general terms marks the boundary between Thailand and Cambodia, however there are exceptions. The region is covered in dry evergreen forest, mixed dipterocarp forest, and deciduous dipterocarp forests. Tree species like Pterocarpus macrocarpus, Shorea siamensis and Xylia xylocarpa var. kerrii dominate. Illegal logging are issues on both, the Thai as well as on the Cambodian side, leaving large hill stretches denuded, vulnerable tree species such as Dalbergia cochinchinensis have been affected.[161] Forest fires are common during the dry season.[162]

Chrey Thom Waterfall Mondulkiri Province

Annamite Range

Lying to the east of the Mekong River, the long chain of mountains called the Annamite Mountains of Indochina and the lowlands that surround them make up the Greater Annamites ecoregion. Levels of rainfall vary from 1,500 - 3,850 mm annually. Mean annual temperatures are about 20 °C. This eco-region contains some of the last relatively intact moist forests in Indochina. Moisture-laden monsoon winds, that blow in from the Gulf of Tonkin ensure pemanent high air humidity. Plants and animals adapted to moist conditions, to seek refuge here and evolve into highly specialized types that are found nowhere else on Earth.[163][164][165]

Ethnically diverse More than 30 ethnic groups of indigenous people live in the Annamites, each with their distinctive and traditional music, language, dress and customs. The natural resources of the Greater Annamites are vital to all of these people.[166]

Eastern Highlands

mountain panorama view in Mondulkiri Province, north-eastern Cambodia, November 2012

Tall grasses and deciduous forests cover the ground east of the Mekong River in Mondulkiri, where the transitional plains merge with the eastern highlands at altitudes from 200–1000 meters. The landscape has suffered from rubber farming, logging and particularly mining, although sizable areas of pristine jungle survive, which are home to rare and endemic wildlife.[167]

Coast

Cambodia's coastal area covers 17,237 km2 (6,655 sq mi), distributed among 4 provinces:

"Until relatively recently, the mangroves of Koh Kong, Cambodia have remained relatively intact. This is partly because of the region’s location — it is an isolated, inaccessible place — and because decades of war and conflict perversely protected the forests from over-exploitation. Local people, however, tended to

"With their roots deep in mud, jagged and gnarled mangrove trees are able to grow in the brackish wetlands between land and sea where other plant life cannot survive. The trees offer refuge and nursery grounds for fish, crabs, shrimp, and mollusks. They are nesting - and migratory sites for hundreds of bird species. They also provide homes for monkeys, lizards, sea turtles, and many other animals as well as countless insects. "[97]

The Cambodian coastline consists of 60,000 ha of some 30 species of mangroves - among the most biologically diverse wetlands on earth.[97] The most pristine mangrove forests are found in Koh Kong Province. In addition to mangroves, sea-grass beds extend throughout the coastal areas, especially in Kampot Province, the Prek Kompong Saom Bay Delta and Kep municipal waters. The meadows are highly productive, but few animals feed directly on the grasses. Those that do tend to be vertebrates such as sea turtles, dabbling ducks and geese.[212][213][214]

mangrove forests in Koh Kong Province Cambodia, September 2013

Coastal habitats

Wetlands cover more than 30 per cent of Cambodia. In addition to the Mekong River and the Tonle Sap floodplain there are the Stung Sen River and the coastal Stung Koh Pao - and Stung Kep estuaries of Koh Kong Province and Kep Province. The freshwater wetlands of Cambodia represent one of the most diverse ecosystems worldwide.[207] The area’s extensive wetland habitats are the product of the annual Mekong maximum, the simultaneous wet season and the drainage paths of a number of minor rivers. See also:Geography of Cambodia#Hydrology The numerous and varied wetlands are Cambodia's central and traditional settlement area, the productive environments for rice cultivation, freshwater fisheries, other forms of agriculture and aquaculture and the constantly growing tourism sector.[208] Considering the eco-region's importance, a variety of plans for local wetland management consolidation exist[209][210] with varying degrees of completion.[211]

coastal wetlands near Ream, Sihanoukville Province

Wetlands

The lake’s flooded forest and the surrounding floodplains are of utmost importance for Cambodia's agriculture as the region represents the cultural heart of Cambodia, the center of the national freshwater fishery industry - the nation's primary protein source.[204] Threats to the lake include widespread pollution, stress through growth of the local population which is dependent on the lake for subsistence and livelihood, over-harvesting of fish and other aquatic - often endangered - species, habitat destruction and potential changes in the hydrology, such as the construction and operation of dams, that disrupt the lake's natural flood cycle. However, concerns that the lake is rapidly filling with sediment seem - according to studies[205] - to be unfounded at the present time.[206]

On higher quality soils or at higher elevation, areas of mixed deciduous forest and semi-evergreen forests[201] occur. This variety of vegetation types accounts for the quantity and diversity of species of the Great Lake ecosystem. Interlocking forest, - grassland and marshland patches provide the many facets and refugiae for the abundant local wildlife.[202][203]

Henri Mouhot: "Travels in the Central Parts of Indo-China" 1864

The Tonle Sap, also known as the Great Lake in central Cambodia is the largest freshwater lake in Southeast Asia and one of the richest inland fishing grounds in the world. The Lake functions as a natural flood water reservoir for the Mekong system as a whole and therefore is an important source of water for the Mekong Delta during the dry season.[198] The ecosystem has developed as a result of the Mekong’s seasonal flow fluctuations. A belt of freshwater mangroves known as the "flooded forest" surrounds the lake. The floodplains in turn are surrounded by low hills, covered with evergreen or deciduous dry forest with prevalent dipterocarp vegetation. The eco-region consists of a mosaic of habitats for a great number of species.[199] The forest gradually yields to bushes and finally grassland with increasing distance from the lake.

The Great Lake ecosystem

The Southern Annamites Montane Rain Forests ecoregion of the montane forests of Kontuey Nea, "the dragon's tail" in the remote north-west of Cambodia, where the boundaries of Cambodia, Laos, and Vietnam meet, is remarkably rich in biodiversity. The relatively intact forests occupy a broad topographic range - from lowlands with wet evergreen forests to montane habitats with evergreen hardwood and conifer forests. The complex geological, topographic and climatic ( rainfall and temperature ) facets that characterize the region make forest structure and composition unique and very variable. There is a unusually high number of near-endemic and endemic species among the many species to be found in the area,. The entire eco-region has a size of 94,000 km2 (36,294 sq mi).[195][196][197]

Southern Annamites Montane Rain Forests ecoregion

According to the Forestry Administration statistics, a total of 380,000 hectares of forest were cleared between 2002 and 2005/2006 - a deforestation rate of 0.5% per year. The main cause of deforestation has been determined to be large-scale agricultural expansions.[193][194]

Cambodia Forest Cover, 2002
Forest Types Area (ha) Percentage
forests - commercially unattractive 3.200.000 30
forests - commercially attractive 630.000 6
flooded forest - cut and/or converted 30
flooded forest - healthy 450.000
lost area 550.000 55
Source: CAMBODIA DEVELOPMENT RESOURCE INSTITUTE [192]
Cambodia Forest Cover, 2002
Forest Types Area (ha) Percentage
Evergreen Forest 3,720,506 20.49
Semi-evergreen forest 1,455,190 8.01
Deciduous forest 4,833,861 26.62
Other forest 1,094,726 6.03
Non-forest 7,056,388 38.85
Source: United Nations [191]

Figures and assessments are numerous as are available sources. as seen in numbers below, which provide a wide range for interpretation. About 69,000 ha (1%) of forest cover is planted forest. Overall Cambodia’s forests contain an estimated 464 million metric tonnes of carbon stock in living forest biomass.[188] Approximately 40% of Cambodia’s Forests have some level of protection, while one of the Cambodia Millennium Development Goals targets is to achieve a 60% forest cover by 2015.[189][190]

Cambodia has one of the highest levels of forest cover in the region as the interdependence of Cambodia’s geography and hydrology makes it rich in natural resources and biological diversity - among the bio-richest countries in Southeast Asia. The Royal Government of Cambodia estimates Cambodia contains approximately 10.36 million hectares of forest cover, representing approximately 57.07% of Cambodia’s land area (2011).[184] On the contrary, international observers and independent sources provide rather different numbers. Consensus permeates, as most sources agree, that deforestation, loss of seasonal wetlands and habitat destruction - among countless minor factors - correlates with the absence of strict administrative control and indifference in law enforcement - not only in Cambodia but the entire region.[185][186][187]

map of forests, vegetation and land use in Cambodia

Vegetation & ecoregions

As the level of the Tonle Sap retreats, it deposits a new layer of sediment. The annual flooding, combined with poor drainage immediately around the lake, transforms the surrounding area into marshlands, unusable for agricultural purposes during the dry season. The sediment deposited into the lake during the Mekong's flood stage appears to be greater than the quantity carried away later by the Tonle Sap River. Gradual silting of the lake would seem to be occurring; during low-water level, it is only about 1.5 meters deep, while at flood stage it is between 10 and 15 meters deep.[182][183]

The flow of water into the Tonle Sap is seasonal. In spring, the flow of the Mekong River, fed by monsoon rains, increases to a point where its outlets through the delta cannot handle the enormous volume of water. At this point, the water pushes northward up the Tonle Sap river and empties into the Tonle Sap lake, thereby increasing the size of the lake from about 2,590 square kilometers to about 24,605 square kilometers at the height of the flooding. After the Mekong's waters crest — when its downstream channels can handle the volume of water — the flow reverses, and water flows out of the engorged lake.

The Mekong River flows southward from the Cambodia-Laos border to a point below Kratie city, where it turns west for about 50 kilometers and then turns southwest to Phnom Penh. Extensive rapids run above Kratie city. From Kampong Cham Province the gradient slopes very gently, and inundation of areas along the river occurs at flood stage—June through November—through breaks in the natural levees that have built up along its course. At Phnom Penh four major water courses meet at a point called the Chattomukh (Four Faces). The Mekong River flows in from the northeast and the Tonle Sap, a river emanating from the Tonle Sap—flows in from the northwest. They divide into two parallel channels, the Mekong River proper and the Bassac River, and flow independently through the delta areas of Cambodia and Vietnam to the South China Sea.

Except for the smaller rivers in the southeast, most of the major rivers and river systems in Cambodia drain into the Tonle Sap or into the Mekong River. The Cardamom Mountains and Elephant Range form a separate drainage divide. To the east the rivers flow into the Tonle Sap, as in the south-west rivers flow into the Gulf of Thailand. Toward the southern slopes of the Elephant Mountains, small rivers flow south-eastward on the eastern side of the divide.

The Mekong River and its tributaries comprise one of the largest river systems in the world.[179] The central Tonle Sap - Great Lake has several input rivers, the most important being the Tonle Sap river during the rainy season, which contributes 62 percent of the total water supply. The other rivers in the sub-basin and direct rainfall on the lake contribute the remaining 38 percent. Other major rivers are the Sen river, Sreng river, Pursat (Pouthisat) river, Sisophon river, Mongkul Borey river, and Sangker river.[180][181]

Mekong tributary, Stung Treng Province
overview Drainage divides
floating homes on the Mekong

Hydrology

Climate data for Senmonorom, Cambodia
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Average high °C (°F) 26.0
(78.8)
27.0
(80.6)
25.0
(77)
19.0
(66.2)
25.0
(77)
25.0
(77)
27.0
(80.6)
25.0
(77)
24.0
(75.2)
25.0
(77)
24.0
(75.2)
27.0
(80.6)
24.9
(76.85)
Average low °C (°F) 14.0
(57.2)
13.0
(55.4)
17.0
(62.6)
13.0
(55.4)
18.0
(64.4)
19.0
(66.2)
20.0
(68)
19.0
(66.2)
18.0
(64.4)
18.0
(64.4)
16.0
(60.8)
15.0
(59)
16.7
(62)
Average precipitation mm (inches) 30.0
(1.181)
48.0
(1.89)
21.0
(0.827)
144.0
(5.669)
90.0
(3.543)
114.0
(4.488)
282.0
(11.102)
555.0
(21.85)
192.0
(7.559)
234.0
(9.213)
129.0
(5.079)
39.0
(1.535)
1,878
(73.936)
Source: world weather online[63]
Climate data for Phnom Penh, Cambodia
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Average high °C (°F) 31.3
(88.3)
32.2
(90)
34.1
(93.4)
35.7
(96.3)
34.3
(93.7)
33.2
(91.8)
32.0
(89.6)
32.8
(91)
32.8
(91)
31.8
(89.2)
30.2
(86.4)
30.7
(87.3)
32.59
(90.67)
Average low °C (°F) 23.9
(75)
23.6
(74.5)
25.4
(77.7)
26.0
(78.8)
26.8
(80.2)
26.3
(79.3)
26.9
(80.4)
25.1
(77.2)
25.2
(77.4)
25.7
(78.3)
24.4
(75.9)
23.5
(74.3)
25.23
(77.42)
Average precipitation mm (inches) 0.0
(0)
11.3
(0.445)
6.5
(0.256)
0.0
(0)
4.8
(0.189)
34.8
(1.37)
16.1
(0.634)
40.3
(1.587)
60.5
(2.382)
65.8
(2.591)
22.7
(0.894)
3.2
(0.126)
266
(10.474)
Source: world weather online[178]
Climate data for Sihanoukville, Cambodia
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Average high °C (°F) 31.3
(88.3)
31.2
(88.2)
32.1
(89.8)
33.7
(92.7)
32.3
(90.1)
31.2
(88.2)
30.0
(86)
30.8
(87.4)
30.8
(87.4)
30.8
(87.4)
31.2
(88.2)
31.7
(89.1)
31.43
(88.57)
Average low °C (°F) 23.9
(75)
24.6
(76.3)
25.4
(77.7)
25.0
(77)
26.8
(80.2)
26.3
(79.3)
25.9
(78.6)
25.1
(77.2)
25.2
(77.4)
24.7
(76.5)
24.4
(75.9)
23.5
(74.3)
25.07
(77.12)
Average precipitation mm (inches) 28.3
(1.114)
25.2
(0.992)
50.3
(1.98)
124.8
(4.913)
207.3
(8.161)
252.7
(9.949)
341.4
(13.441)
377.2
(14.85)
320.6
(12.622)
290.4
(11.433)
138.2
(5.441)
54.4
(2.142)
2,210.8
(87.038)
Source: world weather online[62]

The total annual rainfall average is between 1,000 and 1,500 millimeters (39.4 and 59.1 in), and the heaviest amounts fall in the southeast. Rainfall from April to September in the [28][177]

The maximum mean is about 30 °C ; the minimum mean, about 24 °C. Maximum temperatures of higher than 32 °C, however, are common and, just before the start of the rainy season, they may rise to more than 38 °C. Minimum night temperatures sporadically fall below 20 °C.[174] in January, the coldest month. May is the warmest month - although strongly influenced by the beginning of the wet season, as the area constitutes the easternmost fringe of the south-west monsoon. Tropical cyclones only rarely cause damage in Cambodia.[175][176]

Cambodia's climate, like that of much the rest of mainland Southeast Asia is dominated by monsoons, which are known as tropical wet and dry because of the distinctly marked seasonal differences. The monsoonal air-flows are caused by annual alternating high pressure and low pressure over the Central Asian landmass. In summer, moisture-laden air—the southwest monsoon—is drawn landward from the Indian Ocean. The flow is reversed during the winter, and the northeast monsoon sends back dry air. The southwest monsoon brings the rainy season from mid-May to mid-September or to early October, and the northeast monsoon flow of drier and cooler air lasts from early November to March. Temperatures are fairly uniform throughout the Tonlé Sap Basin area, with only small variations from the average annual mean of around 25 °C (77.0 °F).

Worldwide zones of tropical monsoon climate (Am).
Worldwide zones of Tropical savanna climate (Aw).
Map of rainfall regimes in Cambodia, source: DANIDA

Climate

panorama of Koh Rong Sanloem's west coast, shot from the light-house in the south, Cambodia 2014

Cambodia’s islands fall under administration of the 4 coastal provinces.[171] "There are 60 islands in Cambodia's coastal waters. They include 23 in Koh Kong province, 2 in Kampot province, 22 in Sihanoukville and 13 in Kep city.[sic]"[172] Most islands are, apart from the two small groups of the outer islands, in relative proximity to the coast. The islands and the coastal region of Koh Kong Province are mainly composed of upper Jurassic and lower Cretaceous sandstomne massives.[17] The north-westernmost islands near and around the Kaoh Pao river delta (Prek Kaoh Pao) area are to a great extent sediments of estuaries and rivers, very flat and engulfed in contiguous mangrove marshes.[173]

Islands

The southern mountain ranges drain to the south and west towards the shallow sea. Sediments on the continental shelf are the basis for extensive mangroves marshes, in particular in the Koh Kong province and the Ream National Park.[34][170]

[169]

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