|Freshwater||540||45||No||480||McAllister, D.E., A.L. Hamilton and B. Harvey, 1997|
|Conservation||Mexico is extremely rich in biological diversity and has many endemic species. Currently, 5 per cent (1992) of Mexico’s total land area is protected. Deforestation is extensive: 1.3 per cent (1981-1990) of the total forest area is deforested each year. Mexico and the United States are working together to combat the pollution problems along the industrialized national border. The following information is to be sought: - Status of knowledge of the freshwater fauna; - Existence of conservation plans; - Information on major aquatic habitats or sites within the country; - Current major threats to species; - Future potential threats to species; - Contact(s) for further information.|
|Geography and Climate||
Most of Mexico is an immense, elevated plateau, flanked by mountain ranges that fall away sharply 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 southeast. The Sierra Madre del Sur leads into the Isthmus of Tehuantepec, which lies between the Bay of Campeche and the Gulf of Tehuantepec. Comprising more than half the total area of Mexico, the central plateau slopes downwards from the west to the east and from the south to the north. 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 1,223 kilometres south from the northwestern corner of the country, is traversed by mountains that are a continuation of the coastal ranges in the US state of California. The Yucatan Peninsula, which forms the southeastern tip of the country, is low and flat.
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 metres. The weather here is extremely humid, with temperatures varying from 16° to 49°C. The tierra templada (temperate land) extends from about 914 to 1,830 metres with average temperatures of 17° to 21°C. The tierra fría (cold land) extends from about 1,830 to 2,745 metres. The average temperature range is 15° to 17°C. The rainy season lasts from May to October. Although sections of southern Mexico receive about 990 to 3,000 millimetres (about 39 to 118 inches) of rain per year, most of Mexico is much drier. Rainfall averages less than 635 millimetres (25 inches) annually in the tierra templada, about 460 millimetres in the tierra fría, and about 254 millimetres in the semi-arid north.
Ref. Microsoft, 1996
Mexico has few major rivers. The longest river is the Río Bravo del Norte (=Río Grande), which extends along the Mexican-US border. Other important rivers include the Balsas, Grijalva, and Río Usumacinta in the south and the Conchos in the north. Lake Chapala, in the west, is the largest inland body of water. The Valley of Mexico contains several shallow lakes.
Ref. Microsoft, 1996