II.

Land and Resources

Most of Mexico is an immense, elevated plateau, flanked by mountain ranges that fall sharply off to narrow coastal plains in the west and east. The two mountain chains, the Sierra Madre Occidental to the west and the Sierra Madre Oriental in the east, meet in a region called La Junta in the south-east. At La Junta the two ranges form the Sierra Madre del Sur, a maze of volcanic mountains containing the highest peaks in Mexico (see Sierra Madre). The Sierra Madre del Sur leads into the Isthmus of Tehuantepec, which lies between the Bay of Campeche and the Gulf of Tehuantepec.

The prominent topographical feature of the country is the central plateau, a continuation of the plains of the south-western United States. Comprising more than half the total area of Mexico, the plateau slopes downwards from the west to the east and from the south, where the elevation varies from about 1,830 to 2,440 m (6,000 to 8,000 ft) above sea level, to the north with an elevation of about 1,070 to 1,220 m (3,500 to 4,000 ft). Two large valleys form notable depressions in the plateau: the Bolsón de Mapimí in the north and the Valley of Mexico, or Anáhuac, in central Mexico.

The coastal plains are generally low, flat, and sandy, although the Pacific coast is occasionally broken by mountain spurs. Baja California, a long, narrow peninsula extending about 1,225 km (760 mi) south from the north-western corner of the country, is traversed by mountains that are a continuation of the coastal ranges in the US state of California. The Yucatán Peninsula, which forms the south-eastern tip of the country, is low and flat, averaging about 30 m (100 ft) in elevation.

A.

Rivers and Lakes

Mexico has few major rivers, and most are not navigable. The longest river is the Rio Grande (called the Río Bravo del Norte in Mexico), which extends along the Mexican-US border. Other important rivers include the Balsas Pánuco, Grijalva, and Usumacinta in the south and the Conchos in the north. Mexico has few good harbours. Tampico, Veracruz Llave, and Coatzacoalcos (Puerto México) are major Gulf of Mexico ports. Pacific ports include Acapulco de Juárez, Manzanillo, Mazatlán, and Salina Cruz. Lake Chapala, in the west, is the largest inland body of water. The Valley of Mexico contains several shallow lakes.

B.

Climate

Mexico is bisected by the tropic of Cancer; therefore, the southern half is included in the Torrid Zone. In general, climate varies with elevation. The tierra caliente (hot land) includes the low coastal plains, extending from sea level to about 914 m (3,000 ft). Weather is extremely humid, with temperatures varying from 15.6° to 48.9° C (60° to 120° F). The tierra templada (temperate land) extends from about 914 to 1,830 m (3,000 to 6,000 ft) with average temperatures of 16.7° to 21.1° C (62° to 70° F). The tierra fría (cold land) extends from about 1,830 to 2,745 m (6,000 to 9,000 ft). The average temperature range is 15° to 17.2° C (59° to 63° F). The average temperatures in Mexico City for the months of January and July are 12.6° C (55° F) and 16.1° C (61° F), respectively. The average temperatures in Monterrey for the same months are 14.4° C (58° F) and 27.2° C (81° F).

The rainy season lasts from May to October. Although sections of southern Mexico receive about 990 to 3,000 mm (39 to 118 in) of rain a year, most of Mexico lacks adequate rainfall. Rainfall averages less than 635 mm (25 in) annually in the tierra templada, about 460 mm (18 in) in the tierra fría, and about 254 mm (10 in) in the semi-arid north. Annual precipitation averages for Mexico City and Monterrey are 750 mm (30 in) and 580 mm (23 in) respectively.

C.

Natural Resources

The mineral resources of Mexico are extremely rich and varied. Almost every known mineral is found, including coal, iron ore, phosphates, uranium, silver, gold, copper, lead, and zinc. Proven oil and natural-gas reserves are enormous, with some of the world’s largest deposits located offshore, in the Bay of Campeche. Forests and woodland, which cover about 24 per cent of the land, contain such valuable woods as mahogany, ebony, walnut, and rosewood. Mexico has some of the largest remaining forest reserves, despite the high levels of deforestation. About 12 per cent of the land is suitable for agriculture, but less than 10 per cent receives enough rainfall for raising crops without irrigation.

D.

Plants and Animals

Because of the wide range of temperature, the native flora of Mexico is extremely varied. Cactus, yucca, agave, and mesquite are plentiful in the arid north. The tierra caliente is thickly grown with an immense variety of plants, which form a dense tropical jungle in some areas. The trees in this zone include valuable hardwoods, as well as coconut palms, gum trees, and almond, fig, and olive trees. On the mountain slopes grow oaks, pines, and firs. Arctic vegetation is found at the highest elevations in Mexico.

Mexican fauna also varies according to the climatic zones. Wolves and coyotes are found in the north. The forests on the mountain slopes are inhabited by ocelots, jaguars, peccaries, bears, and pumas. Fur-bearing seals are found on the coasts. A wide variety of reptiles exists, including turtle, iguana, rattlesnake, and lizard. Birds, including sea and game birds, are numerous. Fish are plentiful along the coast and in the river estuaries. Despite this biodiversity many species are on the endangered list.

E.

Environmental Concerns

The long coastlines and mostly mountainous terrain of Mexico provide the greatest variety of ecosystems and biotic habitats on Earth. The country's geographical position has resulted in an eclectic mixing of the flora and fauna from both north and south. Mexico follows only Indonesia, Brazil, and Colombia in richness of biodiversity. It has the highest reptile diversity in the world and the second highest mammal diversity. Nearly one-third of Mexico's terrestrial vertebrates are endemic, and about half of the country's plant species are found nowhere else. Fourteen per cent of the world's fish species inhabit Mexican waters. Mexico's burgeoning population and its heavy resource demands, however, have taken a heavy toll on the environment. Agricultural expansion and farming methods are not well controlled. Soil erosion, salinization, and pollution of watercourses and aquifers with farm chemicals are widespread.

The most acute environmental problems occur in Mexico City, the most populous city in the world. A high concentration of industry, traffic, and domestic energy use plus unfavourable geographical and meteorological conditions have resulted in severe air pollution. The situation is improving, however, as the government introduces controls on traffic and industrial emissions.

The rate of deforestation in Mexico is high—0.9 per cent (1990-1996)—and more and more land is being cleared for agriculture. For example, wet tropical forest, which once covered 6 per cent of the country, has been reduced to half that extent. The most threatened habitats are montane broad-leaved forest, mangroves and coastal wetlands, moist tropical forest, dry tropical forest, and arid zones.

Mexico's heritage of environmental protection dates at least as far back in history as Maya culture, when special forest reserves were recognized and farming proceeded according to an ecological framework. Ancient land-management traditions were lost after the conquest of Mexico by Europeans, and degradation proceeded until the late 19th century, when the modern environmental legacy began. By 1992 there were 68 protected areas in Mexico, including 46 national parks, covering approximately 20 per cent of the country's area. But the extent of many such areas is unclear, and the degree of protection varies depending on the classification of the land, the interpretation of the law, and the government's resolve to enforce it. Therefore, only about 2.4 per cent (1997) of the land is actually protected, and many protected sites are still threatened by deforestation, poaching, dumping, mining, overgrazing, and erosion. Six internationally recognized biosphere reserves have been established within Mexico as part of the United Nations Educational, Scientific, and Cultural Organization (UNESCO) Man and the Biosphere Program.

Mexico is party to a number of international environmental agreements, including on biodiversity, climate change, desertification, endangered species, hazardous wastes, law of the sea, marine dumping, marine life, nuclear test ban, ozone layer, ship pollution, wetlands, and whaling. Regionally, it is responsible under agreements protecting the Caribbean Sea and the Convention on Nature Protection and Wildlife Preservation in the western hemisphere.