**3. Study case**

The Calakmul Biosphere Reserve (CBR) is located at the southeast of Campeche, in the municipality of Calakmul, bordered to the east by the state of Quintana Roo and to the south by the Republic of Guatemala. The natural protected area of Calakmul is characterised by sustaining the ecosystem for different species, as well as being used as a source for water supply for animals and humans. The CBR border coordinates are 19°15′N–90°10′E, 17°45′N–90°10′E, 19°15′N–89°15′ and 17°45′N–89°15′E (**Figure 1**) [28, 29].

The CBR has a very particular climatology, edaphology and vegetation, representing a great contribution to the maintenance of the essential ecological processes, such as water and climate regimes and the ecological and evolutionary processes that determine the biodiversity of the area. Most of the land corresponds to a plateau, originated by the erosion of the limestone, little uneven, interrupted by small hills and micro-valleys. Most of the substrate is composed mainly of carbonated rock (CaCO<sup>3</sup> ) or limestone, and this type of substrate facilitates the filtration and underground transport of water. There are also regions that have more evaporites, rocks formed by the evaporation of marine waters (CaSO4 mainly in the area), which

**Figure 1.** Location of the Calakmul Biosphere Reserve, Campeche. Source [29].

can be dissolved more easily, allowing faster erosion, and alluvium [30]. The composition of the soil allows the development of the karstic system, where water is filtered, dissolving the rock and creating underground tunnels where the liquid finally flows. These tunnels create a drainage system that feeds certain bodies of water located west and northwest of the Yucatan Peninsula, and this process favours the formation of cenotes, aguadas, wetlands, basins, caverns and springs [31].

The biodiversity contains ecosystems characterised by their great diversity, wealth and fragility. Vegetation corresponds to high jungle subperennifolia (25–50% of the trees drop their leaves), medium jungle subperennifolia, medium jungle subcaducifolia (50–75% of the trees lose their leaves), low jungle subperennifolia, savanna, aquatic vegetation and thorny scrub. One important aspect is that roots grow horizontally due to the karstic nature of the area [32–34]. The CBR is allocated in one of the hottest and wettest regions of Mexico. The climate in the CBR is warm and sub-humid with summer rainfall. The average annual precipitation in the region is 1092 mm. Rain is distributed in the months of May to October with 75% of the annual sheet, with an extension of this season until November. The months June to September are the ones observing more abundant precipitation with an average sheet from 135 to 184 mm. The dry season includes the months of December to April, during which the precipitation is less than 50 mm, and the month with the lowest precipitation is February, with an average of 33.9 mm. The average annual temperature is 24–28°C due to the vegetation that regulates it.

García et al. [35] indicated that as two slopes divide the Yucatan Peninsula: the Gulf of Mexico and the Caribbean, and the CBR is allocated in the intermedium area being subject to high scarcity. In addition, there are real water pressure in the surrounding area to use water for social development, which is manifested in the constant colonisation of the area and therefore in the opening of new crop and livestock sites. Virtually, all the rainwater infiltrates, which produces little or no runoff and the local rainfall is concentrated in small superficial storage called "aguadas," which hardly maintain the liquid until the following rainy season. Although legally human activities are restricted in the CBR to a tolerant zone, it is being severely affected by irregular human settlements that eliminate the forest to induce changes in land use.
