Cambodia covers 181,040 square kilometers in the southwestern part of
the Indochina peninsula. It lies completely within the tropics; its
southernmost points are only slightly more than 10� above the equator.
Roughly square in shape, the country is bounded on the north by Thailand
and by Laos, on the east and southeast by Vietnam, and on the west by
the Gulf of Thailand and by Thailand. Much of the country's area
consists of rolling plains. Dominant features are the large, almost
centrally located, Tonle Sap (Great Lake) and the Mekong River, which
traverses the country from north to south.
The climate is monsoonal and has marked wet and dry seasons of
relatively equal length. Both temperature and humidity generally are
high throughout the year. Forest covers about two-thirds of the country,
but it has been somewhat degraded in the more readily accessible areas
by burning (a method called slash-and-burn agriculture), and by shifting
agriculture.
<>Topography
Cambodia falls within several well-defined geographic regions. The
largest part of the country--about 75 percent of the total-- consists of
the Tonle Sap Basin and the Mekong Lowlands. To the southeast of this
great basin is the Mekong Delta, which extends through Vietnam to the
South China Sea. The basin and delta regions are rimmed with mountain
ranges to the southwest (the Cardamom Mountains the Elephant Range) and
to the north (Dangrek Mountains). Higher land to the northeast and to
the east merges into the Central Highlands of southern Vietnam.
The Tonle Sap Basin-Mekong Lowlands region consists chiefly of plains
with elevations generally of less than 100 meters. As the elevation
increases, the terrain becomes more rolling and dissected.
The Cardamom Mountains in the southwest, oriented generally in a
northwest-southeast direction, rise to more than 1,500 meters. The
highest mountain in Cambodia--Phnom Aural, at 1,771 meters--is in the
eastern part of this range. The Elephant Range, an extension running
toward the south and the southeast from the Cardamom Mountains, rises to
elevations of between 500 and 1,000 meters. These two ranges are
bordered on the west by a narrow coastal plain that contains Kampong
Saom Bay, which faces the Gulf of Thailand. This area was largely
isolated until the opening of the port of Kampong Saom (formerly called
Sihanoukville) and the construction of a road and railroad connecting
Kampong Saom, Kampot, Takev, and Phnom Penh in the 1960s.
The Dangrek Mountains at the northern rim of the Tonle Sap Basin
consist of a steep escarpment with an average elevation of about 500
meters, the highest points of which reach more than 700 meters. The
escarpment faces southward and is the southern edge of the Korat Plateau
in Thailand. The watershed along the escarpment marks the boundary
between Thailand and Cambodia. The main road through a pass in the
Dangrek Mountains at O Smach connects northwestern Cambodia with
Thailand. Despite this road and those running through a few other
passes, in general the escarpment impedes easy communication between the
two countries. Between the western part of the Dangrek and the northern
part of the Cardamom ranges, however, lies an extension of the Tonle Sap
Basin that merges into lowlands in Thailand, which allows easy access
from the border to Bangkok.
The Mekong Valley, which offers a communication route between
Cambodia and Laos, separates the eastern end of the Dangrek Mountains
and the northeastern highlands. To the southeast, the basin joins the
Mekong Delta, which, extending into Vietnam, provides both water and
land communications between the two countries.
Cambodia - Climate
Cambodia's climate--like that of the rest of Southeast Asia--is
dominated by the monsoons, which are known as tropical wet and dry
because of the distinctly marked seasonal differences. The monsoonal
airflows 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. The southern
third of the country has a two-month dry season; the northern
two-thirds, a four-month one. Short transitional periods, which are
marked by some difference in humidity but by little change in
temperature, intervene between the alternating seasons. Temperatures are
fairly uniform throughout the Tonle Sap Basin area, with only small
variations from the average annual mean of around 25�C. The maximum
mean is about 28�C; the minimum mean, about 22�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 temperatures
rarely fall below 10�C. January is the coldest month, and April is the
warmest. Typhoons--tropical cyclones--that often devastate coastal
Vietnam rarely cause damage in Cambodia.
The total annual rainfall average is between 100 and 150 centimeters,
and the heaviest amounts fall in the southeast. Rainfall from April to
September in the Tonle Sap Basin-Mekong Lowlands area averages 130 to
190 centimeters annually, but the amount varies considerably from year
to year. Rainfall around the basin increases with elevation. It is
heaviest in the mountains along the coast in the southwest, which
receive from 250 to more than 500 centimeters of precipitation annually
as the southwest monsoon reaches the coast. This area of greatest
rainfall, however, drains mostly to the sea; only a small quantity goes
into the rivers flowing into the basin. The relative humidity is high at
night throughout the year; usually it exceeds 90 percent. During the
daytime in the dry season, humidity averages about 50 percent or
slightly lower, but it may remain about 60 percent in the rainy period.
Cambodia - Rivers
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, while on the west they flow into the Gulf of Thailand. Toward the
southern end of the Elephant Mountains, however, because of the
topography, some small rivers flow southward on the eastern side of the
divide.
The Mekong River in Cambodia flows southward from the CambodiaLaos
border to a point below Kracheh city, where it turns west for about 50
kilometers and then turns southwest to Phnom Penh. Extensive rapids run
above Kracheh city. From Kampong Cham 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 Sab--a river emanating from the Tonle
Sap--flows in from the northwest. They divide into two parallel
channels, the Mekong River proper and the Basak River, and flow
independently through the delta areas of Cambodia and Vietnam to the
South China Sea.
The flow of water into the Tonle Sab is seasonal. In September or in
October, 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 Sab and empties into the Tonle Sap, 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.
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 Sab 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.
Cambodia - Regional Divisions
Cambodia's boundaries in 1987 were for the most part based upon those
recognized by France and by neighboring countries during the colonial
period. The 800-kilometer boundary with Thailand, coincides with a
natural feature, the watershed of the Dangrek Mountains, only in its
northern sector. The 541-kilometer border with Laos and the
1,228-kilometer border with Vietnam result largely from French
administrative decisions and do not follow major natural features.
Border disputes have broken out in the past between Cambodia and
Thailand as well as between, Cambodia and Vietnam.
