By Eugenio Barrios & Sergio Salinas, WWF-Mexico and Bart Wickel, WWF-US
Freshwater ecosystems occupy approximately 1% of the earth’s surface yet possess about 12% of all known animal species. By virtue of their position in the landscape they connect terrestrial and coastal marine biomes and provide and sustain ecosystem services vital to the health and persistence of human communities. These services include the supply of clean water for food production (including freshwater fisheries, aquaculture and agriculture), urban and industrial consumption, among others. Over the past century many freshwater ecosystems around the world have been heavily modified or lost due to the alteration of flow regimes (e.g. due to damming, canalization, diversion, over-abstraction). The synergistic impacts of land use change, changes in flows, chemical deterioration, and climate change have left many systems and their species very little room to adjust to change, while future projections indicate a steady increase in water demand for food and energy production and water supply to suit the needs of a growing world population.
In countries like Mexico, traditionally, the focus has been to secure water for human development and maximize economic growth, which has resulted in allocation of water beyond available amounts for many basins around the country. As a consequence episodic water scarcity severely constrains freshwater ecosystems and the services they provide. Climatic change and variability are presenting serious challenges to a country that already is experiencing serious strain on its water resources.
Mexico, however, is also one of the few countries in the world that by law recognizes freshwater ecosystems as a legitimate user of water, and mandates a flow allocation for the environment (“water reserve” or “environmental flows”). Based on this legal provision the Mexican government through the National Water Commission (CONAGUA), with support of the Alliance WWF – Fundación Gonzalo Río Arronte, has launched a national program to identify and implement “water reserves”: basins where environmental flows are secured and allocated and where the flow regime is protected before over-allocation takes place.
The strategy is to identify and protect basins with an availability of water that is close to their natural flow regime and that also have a high conservation value (based on prior national conservation priority definitions such as protected areas, and biodiversity conservation gap analyses) in order to implement legal restrictions on water resource development. With such protection, these systems will be best positioned to adjust and respond to water shortages, and regime shifts.
To date, 189 basins around the country were identified as potential water reserves (Figure 1). The criteria for selection included a combination of water availability, high biological conservation value, and low water resource demand by current water users. The next step will be the nomination of these water reserves to be integrated in the National Water Reserves Program. This program forms the core of the official Mexican government adaptation strategy towards climate prepared water management, which recognizes that water reserves are the buffer society needs to face uncertainty, and reduce water scarcity risk. Once a water reserve gets implemented environmental annual flow volume gets legally allocated, primarily aimed to buffer against extreme events, especially during water availability shortages due to droughts. The development of activities that alter the natural flow regime such as dams and levees are closely examined, and would potentially be restricted.
To give an example, under current allocation practices, 100% of mean annual runoff (MAR) more gets allocated. In the case of the Acaponeta river in the state of Nayarit, which is one of the 189 potential water reserves, this would mean that in most years there will not be enough flow left in the system to meet human or ecological needs. Based on historic records, the implementation of a water reserve in this basin would allocate 60% of the mean annual runoff (MAR) in Acaponeta River (Figure 1), creating a buffer to secure minimum flows 95% of the time (55 out of 58 years). Legal provisions will be included to allow for adjustments on allocations and water transfers among uses, considering specific priorities agreed on by various stakeholders. The performance of the buffer capacity will be evaluated through a systematic hydrologic and ecological monitoring program and could annually be adjusted.
The ultimate goal of water reserves is to proactively define sustainable limits to water use, and provide water management authorities and users the ability to manage water demand based on actual supply, ultimately reducing user risk and ecosystem vulnerability by preventing water allocation conflicts.