Vietnam GEOGRAPHY
Figure 10. Topography and Drainage, 1987
Vietnam is located in the southeastern extremity of the
Indochinese peninsula and occupies about 331,688 square
kilometers, of which about 25 percent was under cultivation in
1987. The S-shaped country has a north-to-south distance of 1,650
kilometers and is about 50 kilometers wide at the narrowest
point. With a coastline of 3,260 kilometers, excluding islands,
Vietnam claims 12 nautical miles as the limit of its territorial
waters, an additional 12 nautical miles as a contiguous customs
and security zone, and 200 nautical miles as an exclusive
economic zone.
The boundary with Laos, settled, on an ethnic basis, between
the rulers of Vietnam and Laos in the mid-seventeenth century,
was formally defined by a delimitation treaty signed in 1977 and
ratified in 1986. The frontier with Cambodia, defined at the time
of French annexation of the western part of the Mekong River
Delta in 1867, remained essentially unchanged, according to
Hanoi, until some unresolved border issues were finally settled
in the 1982-85 period. The land and sea boundary with China,
delineated under the France-China treaties of 1887 and 1895, is
"the frontier line" accepted by Hanoi that China agreed in 1957-
58 to respect. However, in February 1979, following China's
limited invasion of Vietnam, Hanoi complained that from 1957
onward China had provoked numerous border incidents as part of
its anti-Vietnam policy and expansionist designs in Southeast
Asia. Among the territorial infringements cited was the Chinese
occupation in January 1974 of the Paracel Islands, claimed by
both countries in a dispute left unresolved in the 1980s
(see Foreign Relations
, ch. 4).
Vietnam is a country of tropical lowlands, hills, and densely
forested highlands, with level land covering no more than 20
percent of the area. The country is divided into the highlands
and the Red River Delta in the north; and the Giai Truong Son
(Central mountains, or the Chaîne Annamitique, sometimes referred
to simply as the Chaine), the coastal lowlands, and the Mekong
River Delta in the south.
The Red River Delta, a flat, triangular region of 3,000
square kilometers, is smaller but more intensely developed and
more densely populated than the Mekong River Delta. Once an inlet
of the Gulf of Tonkin, it has been filled in by the enormous
alluvial deposits of the rivers, over a period of millennia, and
it advances one hundred meters into the gulf annually. The
ancestral home of the ethnic Vietnamese, the delta accounted for
almost 70 percent of the agriculture and 80 percent of the
industry of North Vietnam before 1975.
The Red River (Song Hong in Vietnamese), rising in China's
Yunnan Province, is about 1,200 kilometers long. Its two main
tributaries, the Song Lo (also called the Lo River, the Riviere
Claire, or the Clear River) and the Song Da (also called the
Black River or Riviere Noire), contribute to its high water
volume, which averages 500 million cubic meters per second, but
may increase by more than 60 times at the peak of the rainy
season. The entire delta region, backed by the steep rises of the
forested highlands, is no more than three meters above sea level,
and much of it is one meter or less. The area is subject to
frequent flooding; at some places the high-water mark of floods
is fourteen meters above the surrounding countryside. For
centuries flood control has been an integral part of the delta's
culture and economy. An extensive system of dikes and canals has
been built to contain the Red River and to irrigate the rich
rice-growing delta. Modeled on that of China, this ancient system
has sustained a highly concentrated population and has made
double-cropping wet-rice cultivation possible throughout about
half the region
(see Agriculture
, ch. 3;
fig. 10).
The highlands and mountain plateaus in the north and
northwest are inhabited mainly by tribal minority groups. The
Giai Truong Son originates in the Xizang (Tibet) and Yunnan
regions of southwest China and forms Vietnam's border with Laos
and Cambodia. It terminates in the Mekong River Delta north of Ho
Chi Minh City (formerly Saigon).
These central mountains, which have several high plateaus,
are irregular in elevation and form. The northern section is
narrow and very rugged; the country's highest peak, Fan Si Pan,
rises to 3,142 meters in the extreme northwest. The southern
portion has numerous spurs that divide the narrow coastal strip
into a series of compartments. For centuries these topographical
features not only rendered north-south communication difficult
but also formed an effective natural barrier for the containment
of the people living in the Mekong basin.
Within the southern portion of Vietnam is a plateau known as
the Central Highlands (Tay Nguyen), approximately 51,800 square
kilometers of rugged mountain peaks, extensive forests, and rich
soil. Comprising 5 relatively flat plateaus of basalt soil spread
over the provinces of Dac Lac and Gia Lai-Kon Tom, the highlands
accounts for 16 percent of the country's arable land and 22
percent of its total forested land
(see
fig. 1). Before 1975
North Vietnam had maintained that the Central Highlands and the
Giai Truong Son were strategic areas of paramount importance,
essential to the domination not only of South Vietnam but also of
the southern part of Indochina. Since 1975 the highlands have
provided an area in which to relocate people from the densely
populated lowlands.
The narrow, flat coastal lowlands extend from south of the
Red River Delta to the Mekong River basin. On the landward side,
the Giai Truong Son rises precipitously above the coast, its
spurs jutting into the sea at several places. Generally the
coastal strip is fertile and rice is cultivated intensively.
The Mekong, which is 4,220 kilometers long, is one of the 12
great rivers of the world. From its source in the Xizang plateau,
it flows through the Xizang and Yunnan regions of China, forms
the boundary between Laos and Burma as well as between Laos and
Thailand, divides into two branches--the Song Han Giang and Song
Tien Giang--below Phnom Penh, and continues through Cambodia and
the Mekong basin before draining into the South China Sea through
nine mouths or cuu long (nine dragons). The river
is heavily silted and is navigable by seagoing craft of shallow
draft as far as Kompong Cham in Cambodia. A tributary entering
the river at Phnom Penh drains the Tonle Sap, a shallow fresh-
water lake that acts as a natural reservoir to stabilize the flow
of water through the lower Mekong. When the river is in flood
stage, its silted delta outlets are unable to carry off the high
volume of water. Floodwaters back up into the Tonle Sap, causing
the lake to inundate as much as 10,000 square kilometers. As the
flood subsides, the flow of water reverses and proceeds from the
lake to the sea. The effect is to reduce significantly the danger
of devastating floods in the Mekong delta, where the river floods
the surrounding fields each year to a level of one to two meters.
The Mekong delta, covering about 40,000 square kilometers, is
a low-level plain not more than three meters above sea level at
any point and criss-crossed by a maze of canals and rivers. So
much sediment is carried by the Mekong's various branches and
tributaries that the delta advances sixty to eighty meters into
the sea every year. An official Vietnamese source estimates the
amount of sediment deposited annually to be about 1 billion cubic
meters, or nearly 13 times the amount deposited by the Red River.
About 10,000 square kilometers of the delta are under rice
cultivation, making the area one of the major rice-growing
regions of the world. The southern tip, known as the Ca Mau
Peninsula (Mui Bai Bung), is covered by dense jungle and mangrove
swamps.
Vietnam has a tropical monsoon climate, with humidity
averaging 84 percent throughout the year. However, because of
differences in latitude and the marked variety of topographical
relief, the climate tends to vary considerably from place to
place. During the winter or dry season, extending roughly from
November to April, the monsoon winds usually blow from the
northeast along the China coast and across the Gulf of Tonkin,
picking up considerable moisture; consequently the winter season
in most parts of the country is dry only by comparison with the
rainy or summer season. During the southwesterly summer monsoon,
occurring from May to October, the heated air of the Gobi Desert
rises, far to the north, inducing moist air to flow inland from
the sea and deposit heavy rainfall.
Annual rainfall is substantial in all regions and torrential
in some, ranging from 120 centimeters to 300 centimeters. Nearly
90 percent of the precipitation occurs during the summer. The
average annual temperature is generally higher in the plains than
in the mountains and plateaus. Temperatures range from a low of
5°C in December and January, the coolest months, to more than
37°C in April, the hottest month. Seasonal divisions are more
clearly marked in the northern half than in the southern half of
the country, where, except in some of the highlands, seasonal
temperatures vary only a few degrees, usually in the
21°C-28°C
range.
Data as of December 1987
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