Index of Sites with Official Declaration

The six marginal watersheds, plus that of Río Soto La Marina, obtained lower scores (; 2.4 points), which reflects the lack of political instruments for their conservation (Table 5; Figure 1).

The Río Bravo-San Juan watershed exhibited the highest value, with 59.4 points, followed by the Río San Fernando and Río Bravo-Sosa watersheds, with 34.9 and 22.8 points, respectively (Figure 2; tables 1 and 5).

Índice de Sitios con Declaratoria Oficial = Index of Sites with Official Declaration

Figure 2 Index of Sites with Official Declaration of the watersheds of the state of Nuevo León. 

The Río Bravo-San Juan watershed includes 16 natural protected areas (NPAs) covering 18.3 % of the surface area of the state, followed by that of Río Bravo-Sosa, with 13.7 % of its surface area, which encompasses two PNAs and, in the third place, the Sierra Madre Oriental watershed, with 2.6 % and 12 PNAs; the Río San Fernando watershed stands out with seven PNAs, but occupies a mere 0.8 % of the territory of the state (Table 2).

The role of those areas that are protected as water reservoirs is well known. One third of the 105 most populated cities in the world protect their forests because they are the source of the water supply for their inhabitants (^{Dudley and Solton, 2003}; ^{UNEP-WCMC and IUCN, 2016}).

There are four RAMSAR sites in the northeastern region of Mexico -two in Coahuila, one in Tamaulipas and one in Nuevo León: Baño de San Ignacio, with a surface area of 557 ha, located within the Río San Fernando watershed, and covering only 0.06 % of this watershed in Nuevo León (Table 2).

The state comprises 461 environmental management units (EMUs), which cover 9.8 % of its territory; the Río Bravo-Nuevo Laredo basin covers the largest proportion of the state’s surface area (55.1 %) and includes a total of 58 of these conservation and management units (EMUs). Next is Presa Falcón-Río Salado, with 24.5 % of the surface area of the state and 199 EMUs. The third place corresponds to Río San Fernando, with 10.6 % of the surface area of the state and 75 EMUs (Table 2).

Of the 34 PNAs, only two have current management plans. The Río Bravo-San Juan basin has 16 PNAs on a surface area of 360 678 ha, which amounts to 18 % of the state’s territory; this renders it the basin with the largest number and expanse of PNAs in the state. However, only the Cerro de la Silla Natural Monument (6 039 ha) has a current management program. The Río Bravo-Sosa watershed, with two PNAs (without current management programs), covering a surface area of 51 378 ha (13.7 % of the state’s territory) occupies the second place in the state. It is followed by the Sierra Madre Oriental basin, which has 12 PNAs (with obsolete management plans) and a surface area of 22 419 ha, i.e. 2.6 % of the territory. The Río San Fernando watershed has seven PNAs, on 6 911 ha, which amount to less than 1 % of the surface area of the state (Table 2).

The Cumbres de Monterrey National Park belongs to the Río Bravo-San Juan basin and is a particularly important source of water for the MAM, since almost 10 % of the 11 m³ seg^-1 demanded by the city -equivalent to 251 liters per person- are produced only in the locality of La Huasteca (^{Cantú et al., 2010}).

The state of Nuevo León has a huge deficit of conservation areas. Its 34 PNAs cover 7 % of its territory. Today, 14.7 % of the total continental surface area -but only 9.9 % of the surface area of Mexico- is protected (^{Bezaury-Creel et al., 2012}; ^{UNEP-WCMC and IUCN, 2016}). In the tenth meeting of the Conference of the Parties to the Convention on Biological Diversity, in 2010, a revised and updated Strategic Plan was adopted for the 2011-2020 Convention on Biological Diversity, with five objectives and 20 Aichi goals for biodiversity. One of these goals is to conserve at least 17 % of the terrestrial areas through an effective and equitable ecologically representative management and protected areas systems, as well as other effective area-based conservation actions integrated into the landscape and into the broader seascape (^{UNEP-WCMC and IUCN, 2016}).

In the case of Nuevo León, more than 635 000 ha would have to be declared new PNAs, in the next few years, in order to meet the Aichi goal. It is unlikely that this will happen, given that, in the last decade, actions geared toward the protection of the biodiversity have been avoided, as neither financial resources nor specialized technical personnel or sufficient infrastructure and equipment have been allotted to ensure the protection of the natural heritage.

Index of Proposed Priority Sites

The three watersheds with the highest values correspond to the group of marginal basins of Nuevo León: Sierra de Rodríguez (45.3), Río Tamesí (39.1) and Matehuala (36.8) (Table 4; Figure 3). This means that they are located in high biodiversity sites and that they currently lack political instruments for their conservation (PNAs, EMUs, etc.). A large part of their territory is located in the states of San Luis Potosí, Zacatecas and Tamaulipas. As for the main watersheds of Nuevo León, the one with the highest score was that of Río Bravo-San Juan (35.5), followed by that of the Sierra Madre Oriental (27.9) and that of Río Bravo-Sosa (27.2) (Figure 3; Table 4).

Índice de Sitios Prioritarios Propuestos = Index of Proposed Priority Sites

Figure 3 Index of Proposed Priority Sites of the watersheds of Nuevo León. 

Four Priority Hydrological Regions (PHR) exist in the state, which together cover 1 490 317 ha -i.e. 23 % of the total surface area. Most prominent among them is the Río Bravo-San Juan watershed, with 1 045 031 ha in two PHR (Cumbres de Monterrey National Park, and Río San Juan and Río Pesquería), which cover 53 % of their surface area (^{Conabio, 2002}) (Figure 3, Table 3).

As for the eligible areas for the conservation of the biodiversity of Nuevo León, Conabio proposed 464 338 ha, of which 84.7 % are located within three watersheds: the Sierra Madre Oriental, Río Bravo-San Juan and Río San Fernando, plus 526 451 ha, by federal initiative, for the protection of the water services; the three watersheds together -Río Bravo-San Juan, Río Soto La Marina and Río San Fernando- cover 85 % of this surface area (^{Conabio, 2014a}) (Figure 3; Table 3).

A total of 1 835 942 ha, i.e. 29 % of the territory of Nuevo León, consist of epicontinental aquatic hexagons, proposed by ^{Conabio-Conanp (2010)} for prioritizing the fresh water bodies of Mexico. Most prominent is the Río Bravo-San Juan basin, with 213 656 ha of extreme priority hexagons, amounting to 55.5 % of the total surface of these hexagons in Nuevo León (Figure 3; Table 3).

The priority terrestrial hexagons are the result of another exercise carried out by experts, organized by ^{Conabio (2007)} for prioritizing the terrestrial ecosystems with conservation purposes. In Nuevo León, these hexagons comprise a total of 991 332 ha, which amount to 15.6 % of the state’s territory. Notably, three watersheds -Río Bravo-San Juan, Presa Falcón-Río Bravo and Río San Fernando- concentrate 57 % of this priority surface area (Figure 3; Table 3).

Nuevo León includes 26 terrestrial priority regions (TPR) covering 21 % (1 381 491 ha) of its surface area. The Río Bravo-San Juan and Sierra Madre Oriental basins concentrate most (61 %) of the TPRs (^{Arriaga et al., 2000}) (Figure 3; Table 3).

Priority attention sites for conservation were created by ^{Conabio (2016)} through the establishment of categories of extreme, high and medium priority. Such sites occupy 1 721 010 ha (27 % of the surface area of Nuevo León); most prominent are those of the Río Bravo-San Juan and Sierra Madre Oriental basins, with a total of 831 096 ha (Figure 3; Table 3).

Six of the 230 areas of importance for the conservation of birds (AICBs) of Mexico are located in Nuevo León, on a surface area of 844 905 ha, of which 67 % are within the Río Bravo-San Juan and Sierra Madre Oriental basins (^{Cipamex-Conabio, 2015}) (Figure 3; Table 3).

Environmental Impact Index

The two watersheds with the highest values for environmental impact were Río Bravo-San Juan and Río San Fernando, with 60.7 and 40.5 points, respectively (Table 5; Figure 4). Notably, the Presa Falcón-Río Salado and Sierra Madre Oriental basins, which amount to 34 % of the territory of Nuevo León, had relatively low environmental impact indexes, of 37.1 and 18 points, respectively; therefore, decision makers must regard them as priority in order to intensify their exploitation as sources of water, based on the premise of their conservation (Figure 4; Table 4).

Índice de Impacto Ambiental = Index of Environmental Impact

Figure 4 Index of Environmental Impact of the Nuevo León watersheds. 

The Nuevo León watersheds recorded a deficit of -1 601 065 856 Hm³ of water, an equivalent amount to that which the MAM would consume in 3.9 years, at a rate of 13 m³second^-1, which is the current consumption rate of the city (^{Conagua, 2016}). The Río San Fernando basin has the highest negative value, of -309 679 454 Hm³, followed by the Río Bravo-San Juan basin, with -285 762 827 Hm³ (^{Conagua, 2016a}). The balance between the availability and the consumption of water in the 14 watersheds yields negative figures (Table 4).

The Río Bravo-San Juan basin houses the MAM, with 223 inhabitants km^-2, a much higher figure than that of the second most densely populated basin in the state, San Fernando, with 12 inhabitants km^-2, while the national mean is 61 inhabitants km^-2 (^{Inegi, 2017}). 89.6 % of the state’s inhabitants have access to drinking water service. However, there is a marked contrast between the population that inhabits the Río Bravo-San Juan basin, with a 97.8 % coverage of this service, in relation to the inhabitants of the Sierra Madre basin, where the coverage is only 75.8 % (^{Conagua, 2016}) (Table 4). The Río San Juan aquatic ecoregion, which corresponds to the eponymous basin, was the only one in the state that has been rated as highest priority for conservation in all of North America, by ^{Abell et al. (2000)}.

By 2010 there were 4 653 458 inhabitants in Nuevo León (^{Inegi, 2010}), 4.9 % of whom live in 5 185 rural localities (^{Inegi, 2010}). Most of the rural population, which consist of 120 886 inhabitants (53 %), is concentrated in Río Bravo-San Juan. However, this basin also registers the highest number of urban inhabitants. At a global level, cities occupy 3 % of the surface area of the continent. In Nuevo León, urban sprawls cover 104 183 ha, which amount to a mere 1.6 % of the state’s territory (^{Inegi, 2016}); this implies an excessive concentration and centralization of human activities in the state (Table 4).

It has been estimated that one third of the 100 largest cities in the world obtain a considerable proportion of their drinking water from protected forest areas (^{UNEP-WCMC and IUCN, 2016}). In Mexico, every year the PNAs contribute almost 3.4 billion dollars’ worth of environmental services; i.e. for every US dollar of federal public expense allocated to the PNAs, 52 US dollars are recovered in environmental services. Out of these 3.4 billion dollars spent in environmental services, 135.6 million dollars (4 %) correspond to the supply of water for human consumption (^{Bezaury-Creel, 2009}).

Conservation Status Index

Five watersheds registered positive values for the Conservation Status Index: Sierra de Rodríguez, Matehuala, Río Tamesí, Sierra Madre Oriental and Presa San José-Los Pilares. All these, with the exception of Sierra Madre Oriental, cover only a small surface area in Nuevo León, and are therefore regarded as marginal. This means that their conservation attributes are above the environmental impact values. Conversely, negative values for the Conservation Status Index were observed in nine watersheds; which implies that their environmental impacts are greater than their conservation attributes (Table 5, Figure 5).

Índice de Grado de Conservación = Conservation Status Index

Figure 5 Conservation Status Index of the watersheds of Nuevo León. 

The nine remaining watersheds exhibited negative values; i.e. their environmental impacts are above the conservation attributes of sites under official decree (PNAs, EMUs, RAMSAR) and priority sites (TPRs, AICBs, priority hexagons, etc.). The first four watersheds with the highest negative values were: Presa Falcón-Río Salado, with -33.5 points, followed by the marginal watersheds: Río Bravo-Nuevo Laredo, Laguna Madre and Río Bravo-Matamoros-Reynosa, with -27.2, -19.9, and -14.9 points, respectively. The Río Bravo-San Juan and San Fernando basins -the main sources of water for the MAM- exhibited values of -10.8 and -10.1, respectively, which show their high environmental impacts. Although they have the largest number of legal instruments for conservation in Nuevo León, as indicated by their high values for the Index of Sites with Official Declaration, they contain a relatively larger number of PNAs and EMUs than other basins in the state (Table 5; Figure 5).

The Sierra Madre Oriental stands out for its large surface area and its good conservation status; it was the only non-marginal basin in the state that had a positive value for the Conservation Status Index. ^{Aguilar et al. (2010)} point this out in their study aimed at prioritizing the watersheds of Mexico from the perspective of the conservation of biodiversity, in which they registered a positive correlation between the priority level of the watersheds and their level of impact; this means that the level of impact increases as the importance value of the watersheds for conservation grows.

The Río Bravo-Matamoros-Reynosa basin, considered marginal in Nuevo León, registered the second lowest value for the Conservation Status Index (-27.2), due to the scarcity of legal documents for conservation with official declaration and the few proposed priority sites in its territory. Based on the above, this basin occupies the second-to-last place among the state’s basins in terms of conservation status, only after Presa Falcón-Río Salado (-33.5) (Table 5, Figure 5).

Although the Río Bravo-San Juan basin exhibited the highest value for the Index of Sites with Official Declaration (59.4) and the third for the Index of Proposed Priority Sites (35.5), it was the one with the highest Environmental Impact Index (60.7), and therefore it obtained a negative value for the conservation Status index (-10.8) (Table 5, Figure 5).

The Río Bravo-Sosa had the lowest negative value for the Conservation Status Index (-3.7) because it was the third highest value for the Index of Sites with Official Declaration (22.8), but the fourth for the Environmental Impact Index (32.1) (Table 5, Figure 5).

The Presa Falcón-Río Salado basin stands out for being the one with the lowest value for the Conservation Status Index (-33.5) among the fourteen watersheds in the state; it obtained the third place for the Environmental Impact Index (37.1) (Table 5, Figure 5).

The Río Bravo-Nuevo Laredo basin registered the fourth highest negative value for the Conservation Status Index (-14.9), having had the fourth value for the Environmental Impact Index (28.2) (Table 5, Figure 5).

Although Río Soto La Marina exhibited the lowest value for the Index of sites with Official Declaration (0.7) among the non-marginal basins, it registered a relatively low value for the Conservation Status Index (-5.0) (Table 5, Figure 5).

The Laguna Madre basin, regarded as marginal, obtained the third lowest value for the Conservation Status Index (-19.9), as a result of the scarcity of legal instruments for conservation with official declaration, and of the low number of priority sites proposed in its territory (Table 5, Figure 5).

The Presa San Fernando basin stands out for being the one with the second highest value for the Environmental Impact Index (40.5), as well as for the Index of Sites with Official Declaration (34.9) (Table 5, Figure 5).

Although the Río Tamesí watershed, regarded as marginal in Nuevo León, recorded a very low value for the Index of Sites with Official Declaration (0.7), it exhibited a positive value for the Conservation Status Index (16.59) (Table 5, Figure 5). Sierra Madre Oriental stands out for being the only non-marginal basin with a positive value for the Index of Sites with Official Declaration (11.0) (Table 5, Figure 5).

The Matehuala, Sierra de Rodriguez and Presa San José-Los Pilares basins had positive values for the Conservation Status Index and stand out for their extremely low values (< 1.5) for the Index of Sites with Official Declaration.

Finally, the Sierra Madre marginal basin exhibited a negative value for the conservation Status Index (-7.4) (Table 5, Figure 5).

The methodology employed to generate the indexes of the present study considers the environmental variables of biodiversity and governance attributes, and of environmental impacts as cited by other authors to prioritize the watersheds and aquatic ecoregions at a national and continental scale (^{Abell et al., 2000}; ^{Valencia et al., 2007}; ^{Aguilar et al., 2010}).

The results make it possible to prioritize the watersheds according to the various indexes in order to implement actions geared at improving the conditions of the basins of Nuevo León.