Satellite view of the Yucatán Peninsula
The Yucatán Peninsula is bordered by the Caribbean Sea to the east and by the Gulf of Mexico to the north and west. It can be delimited by a line running from the Laguna de Términos on the Gulf coast through to the Gulf of Honduras on the Caribbean coast. It incorporates the modern Mexican states of Yucatán, Quintana Roo and Campeche, the eastern portion of the state of Tabasco, most of the Guatemalan department of Petén, and all of Belize. Most of the peninsula is formed by a vast plain with few hills or mountains and a generally low coastline. A 15-kilometre (9.3 mi) stretch of high, rocky coast runs south from the city of Campeche on the Gulf Coast. A number of bays are situated along the east coast of the peninsula, from north to south they are
Espíritu Santo Bay, Chetumal Bay and Amatique Bay. The north coast features a wide, sandy littoral zone. The extreme north of the peninsula, roughly corresponding to Yucatán State, has underlying bedrock consisting of flat Cenozoic limestone. To the south of this the limestone rises to form the low chain of Puuc Hills, with a steep initial scarp running 160 kilometres (99 mi) east from the Gulf coast near Champotón, terminating some 50 kilometres (31 mi) from the Caribbean coast near the border of Quintana Roo. The hills reach a maximum altitude of 170 metres (560 ft).
The northwestern and northern portions of the Yucatán Peninsula experience lower rainfall than the rest of the peninsula; these regions feature highly porous limestone bedrock resulting in less surface water. This limestone geology results in most rainwater filtering directly through the bedrock to the phreatic zone, from whence it slowly flows to the coasts to form large submarine springs. Various freshwater springs rise along the coast to form watering holes. The filtering of rainwater through the limestone has caused the formation of extensive cave systems. These cave rooves are subject to collapse forming deep sinkholes; if the bottom of the cave is deeper than the groundwater level then a cenote is formed.
In contrast, the northeastern portion of the peninsula is characterised by forested swamplands. The northern portion of the peninsula lacks rivers, except for the Champotón River – all other rivers are located in the south. The Sibun River flows from west to east from south central Quintana Roo to Lake Bacalar on the Caribbean Coast; the Río Hondo flows northwards from Belize to empty into the same lake. Bacalar Lake empties into Chetumal Bay. The Río Nuevo flows from Lamanai Lake in Belize northwards to Chetumal Bay. The Mopan River and the Macal River flow through Belize and join to form the Belize River, which empties into the Caribbean Sea. In the southwest of the peninsula, the San Pedro River, the
Candelaría River and the
Mamantel River, which all form a part of the Gulf of Mexico drainage.
The Petén region consists of densely forested low-lying limestone plain featuring karstic topography. The area is crossed by low east–west oriented ridges of Cenozoic limestone and is characterised by a variety of forest and soil types; water sources include generally small rivers and low-lying seasonal swamps known as bajos. A chain of fourteen lakes runs across the central drainage basin of Petén; during the rainy season some of these lakes become interconnected. This drainage area measures approximately 100 kilometres (62 mi) east–west by 30 kilometres (19 mi) north–south. The largest lake is Lake Petén Itza, near the centre of the drainage basin; it measures 32 by 5 kilometres (19.9 by 3.1 mi). A broad savannah extends south of the central lakes. To the north of the lakes region bajos become more frequent, interspersed with forest. In the far north of Petén the Mirador Basin forms another interior drainage region. To the south the plain gradually rises towards the Guatemalan Highlands. The canopy height of the forest gradually decreases from Petén northwards, averaging from 25 to 35 metres (82 to 115 ft). This dense forest covers northern Petén and Belize, most of Quinatana Roo, southern Campeche and a portion of the south of Yucatán State. Further north, the vegetation turns to lower forest consisting of dense scrub.
The climate becomes progressively drier towards the north of the peninsula. In the north, the annual mean temperature is 27 °C (81 °F) in Mérida. Average temperature in the peninsula varies from 24 °C (75 °F) in January to 29 °C (84 °F) in July. The lowest temperature on record is 6 °C (43 °F). For the peninsula as a whole, the mean annual precipitation is 1,100 millimetres (43 in). The rainy season lasts from June to September, while the dry season runs from October to May. During the dry season, rainfall averages 300 millimetres (12 in); in the wet season this increases to an average 800 to 900 millimetres (31 to 35 in). The prevailing winds are easterly and have created an east-west precipitation gradient with average rainfall in the east exceeding 1,400 millimetres (55 in) and the north and northwestern portions of the peninsula receiving a maximum of 800 millimetres (31 in). The southeastern portion of the peninsula has a tropical rainy climate with a short dry season in winter.
Petén has a hot climate and receives the highest rainfall in all Mesoamerica. The climate is divided into wet and dry seasons, with the rainy season lasting from June to December, although these seasons are not clearly defined in the south; with rain occurring through most of the year. The climate of Petén varies from tropical in the south to semitropical in the north; temperature varies between 12 and 40 °C (54 and 104 °F), although it does not usually drop beneath 18 °C (64 °F). Mean temperature varies from 24.3 °C (75.7 °F) in the southeast to 26.9 °C (80.4 °F) in the northeast. Highest temperatures are reached from April to June, while January is the coldest month; all Petén experiences a hot dry period in late August. Annual precipitation is high, varying from a mean of 1,198 millimetres (47.2 in) in the northeast to 2,007 millimetres (79.0 in) in central Petén.