Geography of Bolivia
The geography of Bolivia is unique among the nations of South America. Bolivia is one of two landlocked countries on the continent, and also has the highest average altitude. The main features of Bolivia's geography include the Altiplano, a highland plateau of the Andes, and Lake Titicaca (Lago Titicaca), the largest lake in South America and the highest commercially navigable lake on Earth (which it shares with Peru).
Area and location
Bolivia comprises 1,098,580km² of territory, of which 14,190km² is water. This makes the nation's size roughly comparable to the size of Texas and California combined, slightly less than three times the size of Montana, or twice the size of Spain. Bolivia is located in the west-central part of South America. It borders five nations with a total of 6,743km of borders; of these, the longest is the 3,400km northeastern border with Brazil. Bolivia also neighbors Peru, with a 900km border to the northwest and shared control of Lake Titicaca. Smaller borders include Chile (southwest; 861km), Argentina (south; 832km) and Paraguay (southeast; 750km).
Geographic regions
Stretching in a broad arc across western Bolivia, the Andes define the country's three geographic zones: the mountains and Altiplano in the west, the subtropical Yungas and temperate valleys of the eastern mountain slopes (the western part of the Amazon Rainforest), and the tropical lowlands or plains (llanos) of the eastern lowlands, or Oriente. The Andes run in two great parallel ranges (cordilleras). The western range (Cordillera Occidental) runs along the Peruvian and Chilean borders. The eastern range (Cordillera Oriental) is a broad and towering system of mountains stretching from Peru to Argentina. Between the two ranges lies the Altiplano, a lofty plateau 805km long and 129km wide.
Climate
Although Bolivia lies entirely within tropical latitudes, climatic conditions vary widely from tropical in the lowlands to polar in the highest parts of the Andes. Temperatures depend primarily on elevation and show little seasonal variation. In most locations, rainfall is heaviest during the Southern Hemisphere summer, and yearly amounts tend to decrease from north to south.
Northern lowland areas have a tropical wet climate with year-round high temperatures, high humidity, and heavy rainfall. Daytime highs average more than 30° C all year in most locations. The rain-bearing northeast trade winds, blowing across the Amazon Basin, bring significant rainfall amounts. Rain often falls in brief thunderstorms, sometimes accompanied by strong winds and hail.
Central lowland areas have a tropical wet and dry climate. From October through April, northeast trade winds predominate, and the weather is hot, humid, and rainy. From May through September, however, dry southeast trade winds take control, and precipitation is minimal. During this season, clear days and cloudless nights allow for higher daily maximums and lower nightly minimums than occur during the rainy season. Occasional incursions of strong winds from the south, called surazos, can reach this region during winter and bring cool temperatures for several days.
The Chaco has a semitropical, semiarid climate. The northeast trade winds bring rain and hot humid conditions only from January through March; the other months are dry with hot days and cool nights. Bolivia's highest maximum temperature, 47° C, was recorded here. Surazos also affect the Chaco; their approach is usually signaled by a squall line.
Temperatures and rainfall amounts in mountain areas vary considerably. The Yungas, where the moist northeast trade winds are pushed up by the mountains, is the cloudiest, most humid, and rainiest area, receiving up to 152 centimeters annually. Sheltered valleys and basins throughout the Cordillera Oriental have mild temperatures and moderate rainfall amounts, averaging from 64 to 76 centimeters annually. Temperatures drop with increasing elevation, however. Snowfall is possible at elevations above 2,000 meters, and the permanent snow line is at 4,600 meters. Areas over 5,500 meters have a polar climate, with glaciated zones. The Cordillera Occidental is a high desert with cold, windswept peaks.
The Altiplano, which also is swept by strong, cold winds, has an arid, chilly climate, with sharp differences in daily temperature and decreasing amounts of rainfall from north to south. Average highs during the day range from 15°C to 20°C, but in the summer tropical sun, temperatures may exceed 27° C. After nightfall, however, the thin air retains little heat, and temperatures rapidly drop to just above freezing. Lake Titicaca exerts a moderating influence, but even on its shores, frosts occur in almost every month, and snow is not uncommon.
Valleys
The northeastern flank of the Cordillera Real is known as the Yungas, from the Aymara word meaning "warm valleys." The steep, almost inaccessible slopes and peaks of this mainly semitropical valley area northeast of La Paz offer some of the most spectacular scenery in Bolivia. Rainfall is heavy, and lush vegetation clings to the sides of narrow river valleys. The land is among the most fertile in Bolivia, but poor transportation has hindered its agricultural development. The government attempted to build a railroad through the Yungas in 1917 to connect La Paz with the eastern lowlands. The railroad was abandoned, however, after completion of only 150 kilometers.
The eastern slopes of the Cordillera Central descend gradually in a series of complex north-south ranges and hills. Rivers, draining to the east, have cut long narrow valleys; these valleys and the basins between the ranges are favorable areas for crops and settlement. Rich alluvial soils fill the low areas, but erosion has followed the removal of vegetation in some places. The valley floors range from 2,000 to 3,000 meters above sea level, and this lower elevation means milder temperatures than those of the Altiplano. Two of Bolivia's most important cities, Sucre and Cochabamba, are located in basins in this vast region.
Lowlands
The eastern lowlands include all of Bolivia north and east of the Andes. Although comprising over two-thirds of the national territory, the region is sparsely populated and, until recently, has played a minor role in the economy.
Differences in topography and climate separate the lowlands into three areas. The flat northern area, made up of Beni and Pando departments and the northern part of Cochabamba Department, consists of tropical rainforest. Because much of the topsoil is underlain by clay hardpan, drainage is poor, and heavy rainfall periodically converts vast parts of the region to swamp. The central area, comprising the northern half of Santa Cruz Department, has gently rolling hills and a drier climate than the north. Forests alternate with savanna, and much of the land has been cleared for cultivation. Santa Cruz, the largest city in the lowlands, is located here, as are most of Bolivia's petroleum and natural gas reserves. The southeastern part of the lowlands is a continuation of the Chaco of Paraguay. Virtually rainless for nine months of the year, this area becomes a swamp for the three months of heavy rains. The extreme variation in rainfall supports only thorny scrub vegetation and cattle grazing, although recent discoveries of natural gas and petroleum near the foothills of the Andes have attracted some settlers to the region.
Most of Bolivia's important rivers are found in the water-rich northern parts of the lowlands, particularly in the Alto Beni (Upper Beni), where the land is suitable for crops such as coffee and cacao. The northern lowlands are drained by wide, slow-moving rivers, the three largest of which--the Mamoré, Beni, and Madre de Dios—all flow northward into the Madeira River in Brazil and eventually into the Amazon. Riverboats along the Beni and the Mamoré carry both passenger and freight traffic; rapids on the Madeira prevent river traffic farther into Brazil. Near the Paraguayan border, shallow sandy streams carry the seasonal runoff into the Pilcomayo or Paraguay rivers.