Climate & Geomorphology

CLIMATE

The Yucatan Peninsula falls entirely within the Northern Region of the Tropic of Cancer with rainfall amounts that increase the farther south and inland one goes. Average annual rainfall ranges from less than 30 inches in the driest parts of the northwest (northern Campeche, Yucatan and Quintana Roo) up to 2,000 mm (80 inches) in the Petén region to the south. Rainfall varies seasonally, with June to November generally the wettest months. The rains mainly occur in the form of downpours or thunderstorms in late afternoon, however, thunderstorms may unexpectedly occur at any moment of the day.

The graphs below (from https://www.worlddata.info/) show the ranges in relative and absolute humidity and rain days per year.

Warm air can absorb more moisture than cold air. The relative humidity indicates how much moisture can be physically contained in the air. At high humidity, a person feels uncomfortable and perceives this as oppressive. In general, a relative humidity of 40-60% feels pleasant. With humidity averaging 86%, September is the most uncomfortable. In March, on the other hand, it is easier to endure.

In warm months, there is also a higher absolute humidity almost everywhere. At a temperature of 25°C, air can absorb up to 23 grams of water per cubic meter. At 20°C, it is only 17.3 grams. A relative humidity of 40% at 25°C thus corresponds to an absolute humidity of 9.2 grams of water. From a proportion of approx. 13.5 grams, humans perceive the air as muggy. This limit is exceeded throughout the year in Yucatan Peninsula.

A rain day is a day on which at least 0.1 mm precipitation (=0.1 liter) per square meter falls. This can be rain, snow, hail or even dew. So it does not have to rain the whole day. With 14 rain days, September offers the most rain days, while April has the fewest.

GEOMORPHOLOGY

You can think of the Peninsula as a big slab of limestone gently tilted toward the sea all around. The farther south you go, the more likely you are to encounter low hills. By the same token, you must travel far offshore before you reach deep water.

tHE BEDROCK IS LIMESTONE.

Limestone is soluble in water so the Yucatan's limestone bedrock is honeycombed with caves and sinkholes -- it's classic karst topography. Yucatan's sinkholes have a special name -- cenotes (seh-NO-tehs). Cenotes are the result of caves collapsing, forming holes in the ground with water in the bottoms of the holes. Because the limestone has so many holes in it, there are no major rivers throughout the entire Yucatan Peninsula. Water runs underground.

THE LIMESTONE IS YOUNG, GEOLOGICALLY SPEAKING

Much of the outcropping limestone in the northern Yucatan is part of the Carrillo Puerto Formation of Miocene-Pliocene age. The Miocene and Pliocene are often considered as having occurred from 23.8 to 1.8 million years ago. Along much of the Yucatan coastline you find Quaternary deposits 1.8 million years old and younger. (Jim Conrad https://www.backyardnature.net/yucatan/geology~.htm)

THE YUCATAN PENINSULA KARST AQUIFER

Karst is a landscape with distinctive hydrology and landforms that arise when the underlying rock is soluble. Although karst can develop on evaporate rocks such as gypsum and siliceous rocks such as quartzite, the vast majority of karst landforms are found on carbonate rocks, such as limestones. Karst landscapes may have sinkholes, caves, enclosed depressions, disappearing streams, springs and sinkholes.
(https://www.gsi.ie/en-ie/programmes-and-projects/groundwater/activities/understanding-irish-karst/Pages/What-is-karst.aspx)

The Yucatán Peninsula karst aquifer is one of the most extensive and spectacular karst aquifer systems on the planet. This transboundary aquifer system extends over an area of approximately 165,000 km2 in México, Guatemala and Belize.
(Bauer-Gottwein, P., Gondwe, B.R.N., Charvet, G. et al. Review: The Yucatán Peninsula karst aquifer, Mexico. Hydrogeol J 19, 507–524 (2011). https://doi.org/10.1007/s10040-010-0699-5)

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