There is no standard definition for the drylands region between the United States and Mexico. The desert region extends from Central Mexico northward through California, Nevada, Arizona, New Mexico, and Texas. In terms of climate, however, warming and moisture trends show similar changes from as far south as Guatemala to as far north as Canada.1 A large portion of Mexico’s water supply originates from the U.S. Colorado River Basin. International commerce extends the region even further. Culturally, the region is composed of several metropolitan centers, as well as rural and tribal areas, such as the Tohono O’odham lands that cross the U.S.-Mexico border and include federally recognized tribal land in Arizona.2
To put the topic in context for the workshop, this session covered a definition of the term “transboundary region,” key sustainability challenges and vulnerabilities with a particular focus on binational water management, and current binational and regional research approaches in the region.
Robert Washington-Allen (University of Nevada, Reno) and María Amparo Martínez Arroyo (Instituto Nacional de Ecología y Cambio Climático [by Webcast]) noted that there are hundreds of definitions of
1 See https://sites.ualberta.ca/~ahamann/data/climatena.html [July 2018].
drylands and rangelands,3 and the area is commonly defined on the basis of the issue being studied, such as land cover, land use, or land degradation. The U.S. Environmental Protection Agency (EPA)4 and the U.S. Forest Service5 have their own sets of definitions for these ecoregions, and another is provided by the U.N. Convention to Combat Desertification, which developed a widely used aridity index to define drylands.6 The U.N. index determines aridity by dividing the mean annual precipitation by the mean potential evapotranspiration. Based on this calculation, drylands cover 41 percent of all terrestrial land surface, including 45 percent of the United States and 65 percent of Mexico.
Washington-Allen listed the main uses for drylands areas:
- plant production for foraging, energy, and timber;
- livestock production for meat, hides, fiber, milk, energy (manure), and construction (adobe);
- wildlife habitat management and preservation;
- water catchments for water storage;
- open space for recreation—camping, hunting, fishing, photography, wind farming; and
- lumber and mineral production.
He added that mining was also becoming increasingly popular in drylands areas, and he noted that the drylands region comprised a very complex system.
Washington-Allen said scientists have been curious in recent years about how much carbon is produced in this ecosystem as a result of climate change. Historically, drylands were considered low-productivity systems. Although there is still much to learn about carbon dynamics in drylands ecosystems, recent studies are showing that when efficiently irrigated and used, arid and hyper-arid areas can become large carbon sinks—comparable to and at times even surpassing carbon absorption by forest areas. He said that data also show positive greening trends in drylands areas over the past two decades.
Washington-Allen noted, however, that these kinds of areas are still highly variable. He used a graphic depicting plant phenology over time
3 See Lund, H. (2007). Accounting for the world’s rangelands. Rangelands, 29(1); he found more than “300 published definitions of grasslands, grazing lands, pasture, shrubland, and rangeland.”
5 See https://www.fs.fed.us/research/highlights/highlights_display.php?in_high_id=984 [November 2018].
in the Sudan region to show the high variability in arid rangelands from year to year, with averages falling significantly below the rates for semiarid areas. He cited another study7 on phenological responses to climate change that shows, across the globe, that drylands regions tend to have the most unstable plant growth both during the year and from year to year. Washington-Allen said many scientists wonder whether the drylands climate is changing in the same way that other area climates are changing. For such analyses, researchers8 have used temporal gradients to calculate the velocity of temperature change globally. By overlaying measurement systems, one can determine how quickly an ecosystem is moving and how much “residence time” there is in any particular area.
Using the state of Texas as an example, Washington-Allen described the relationship between precipitation and temperature in drylands areas. He and his colleagues studied the drought in 2011 and found that it adversely affected every species in the region. He stated that more than 300 million trees died during the drought, which started what scientists referred to as a range shift. He noted that how one defines the extent of the shift depends on the scale, context, and period of time over which the changes are measured. It also depends on the observer’s perspective: an ecologist may view a system differently than a geomorphologist, and the area’s local residents may view the system in another, entirely different way.
Washington-Allen said that considering the drylands area as a single region, one should look at what is shared at and among the boundaries. There are corridors and linkages, buffer zones, and natural protected areas on both sides of the U.S.-Mexico border. The shared ecosystems in the border region have an enormous natural value and include several conservation core areas—terrestrial, hydrological, and avian. He listed the Sonoran and Chihuahuan deserts, the Rio Grande and Rio Bravo rivers, the Colorado River delta, and the Laguna Madre as primary examples of the ecological richness and diversity in the binational region. There are also shared challenges in the region, including pollution; land degradation; and water quality, quantity, and instability. He said it is the job of the stakeholder community (including people in public health, environmental health, sustainability, development, and education) to develop and implement strategies to deal with those challenges.
Martínez Arroyo added that in light of the drylands’ dynamic conditions in the context of climate change, including loss of biodiversity and
7 White, M.A., Hoffman, F., Hargrove, W.W., and Nemani, R.R. (2005). A global framework for monitoring phenological responses to climate change. Geophysical Research Letters, 32(4), l04705. doi: 10.1029/2004gL021961.
8 See, for example, Loarie, S.R., Duffy, P.H., Hamilton, H., Asner, G.P., Field, C. B., and Ackerly, D.D. (2009). The velocity of climate change. Nature, 462, 1052–1055.
numerous socio-environmental issues, it could benefit the region to put together think-tank groups to develop targeted interventions. Having a clearly defined area of reference, as well as a clear understanding of the specific problems, may help with selecting the appropriate study topics and multidisciplinary groups to address the issues.
In the discussion that followed the presentation, Laureano Alvarez (North American Development Bank) noted that the Border 2020 binational agreement between the U.S. Environmental Protection Agency (EPA) and the Mexican Secretariat of Environment and Natural Resources (SEMARNAT) (see Chapter 1) administratively defines the border region as an east-west area of approximately 2,000 miles (3,100 kilometers) from the Gulf of Mexico to the Pacific Ocean and a north-south area of 62.15 miles (100 km) on each side of the international border.9 He added that water is the largest shared binational resource, with the Colorado River, the Rio Bravo, and the Rio Conchos (which rises in Chihuahua) being the primary sources. Species migration, he said, is another factor that should be considered when looking at the region in its entirety. Washington-Allen responded that context and granularity would be important when determining a particular geographic range for research. The range may vary on the basis of the subject being measured and the data that are available on that topic. Christopher Scott added that as a group tries to build a larger study to further explore sustainability in the region, how it defines the area and its key challenges may be contingent on the researchers and stakeholders involved in the identification of problems and solutions.
Ana Escalante Hernández (Universidad Nacional Autónoma de México, UNAM) commented on the importance of binational collaboration in addressing key sustainability issues. Although it may prove challenging and complex to work with researchers and stakeholders from different areas, she said having done so has helped her put the issues in better perspective. Scott noted that both multisector collaboration and a need to clearly define the area of research interest and work on a shared solution are both important.
Christopher Scott (Steering Committee Chair) opened his presentation10 by showing a map of the arid regions in North, Central, and South America, and a graphic depicting how climate change is projected to expand
9 See https://www.epa.gov/sites/production/files/documents/border2020summary_0.pdf [August 2018].
10 Scott noted that his presentation was a collaboration between himself and two other steering committee members, Kelly Twomey Sanders and Alfonso Cortez Lara.
the areas in the southwestern United States and northwestern Mexico that experience more than 20 days of 100-plus-degree temperatures (F) in a year. He referred to the U.S.-Mexico drylands area as the “bullseye of climate change,” noting that high temperatures and high variability in precipitation are both significant in this area. These factors bring about key environmental, social, and economic challenges.
Scott talked about the impact of extended high temperatures on precipitation and water management, from how it affects the snow and soil on mountaintops to how the increased salinity and decreased water storage capacities create major usage challenges. Using the Hoover Dam as an example, he noted that the dam’s storage decreased by 60 percent between 1983 and 2018. He said that the drylands area is reaching a critical point at which water demand and supply forecasts all point toward increasing competition for water across various sectors and uses (industrial, agricultural, etc.) over time. According to the U.S. Bureau of Reclamation,11 the demand for water is going to continue to rise above the current and projected supply. Hydric planning will become increasingly important to ensure water security, that is, to maintain sufficient quality and quantity for human consumption and a resilient ecosystem.
Scott said the key to binational water management is determining which guidelines and policies will work best on both sides of the border. There are similarities on both sides—climate, landscape, natural resources, and rapid urbanization—but there are marked differences in culture, language, legislation, economy, infrastructure, education, and research capacities. Any water resources infrastructure put in place would need to be adaptable, suitable for the long term, and inclusive of all levels of government (federal, state, local, and municipal). He added that it will also be essential to include nongovernmental institutions in the governance planning and to encourage citizen participation and engagement. Scott acknowledged that while each country and other jurisdictions may have its own legal framework and decision-making process, it is still possible to confer jointly on the diagnosis of key issues and the proposal and implementation of solutions. He cited the binational Minute 319 (which redefined the allotment of Colorado River water to Mexico) and Minute 323 (which extended Minute 319 through 2026 and added a Binational Water Scarcity Contingency Plan) as examples of successful transboundary collaborations.12
Scott addressed future water governance challenges, including con-
12 The Minute system is a way to adopt certain kinds of modifications to the 1944 treaty between the United States and Mexico to share water resources in the Colorado and Rio Grande basins. Available: https://pulseflow.arizona.edu/minute-319 [August 2018] and https://www.ibwc.gov/Files/CF_CR_Minute_323_102517.pdf [August 2018].
servation, storage (reservoirs and aquifers), treatment, and reuse. He also differentiated between water demand management and water shortage management: if policy makers emphasize dealing with the shortage alone, they are allocating water that no longer exists. Then, in the future, when water demand exceeds water availability, to whom does the shortage apply? Regarding water treatment—specifically, desalinization—Scott noted that the cost must be weighed against the benefit. He said that it is difficult and costly to desalinate seawater for crop irrigation and may not be a justifiable process considering the high volumes of water needed for agriculture. However, desalinization may be a worthwhile process for urban water storage for human consumption.
Scott said that people often think of arid regions as being rural areas—vast deserts or small towns—but they actually also include urban landscapes, with clusters of heavy populations and high economic activity. The population and economic growth in urban areas, however, is not equal on both sides of the border. Mexican border cities, such as Tijuana, Juarez, and Matamoros, tend to have larger populations than their U.S. counterparts. He said that in Mexico, industrial activity (maquiladoras) continues to be a driver of water demand, while also generating employment. The infrastructure and high concentrations of people in urban settings present specific risks and can leave those areas vulnerable to environmental hazards, such as hurricanes. He also noted that in the future, mining is expected to become more prominent, which will shift water demand and economic activity towards rural areas.
Urbanization also raises the need to consider water in the context of providing food and energy. Generating electricity consumes large quantities of water; conversely, treating water requires large amounts of energy. Fracking, another rapidly growing activity in the drylands region on the U.S. side of the border, also requires significant amounts of water, with impacts on both quantity and quality. Citing the 2018 World Factbook,13 Scott noted that while improving energy efficiency is a key step in sustainability, it is not the same as, and may not translate to, saving water. Mexico is the 11th largest producer of oil in the world and the 16th largest consumer of energy. However, 3.9 percent of the population lacks access to improved drinking water sources (7.9% in rural areas), 14.8 percent of the population lacks access to adequate sanitation (25.5% in rural areas), and reservoirs are becoming increasingly depleted and contaminated.
Scott noted that agricultural use and irrigation in Mexico consume 90 percent of the total volume of groundwater. The water belongs to the nation, and users enter into concession rights agreements that establish limits for water use including groundwater exploitation. Scott also noted how
Mexico’s electricity Tarifa 09 (tariff number 09), which provides subsidies for energy used in low-voltage agricultural pumping and irrigation14,15 has led to overexploitation of groundwater by individuals wanting to take advantage of the cost incentive. He said that effective enforcement of the tariff and consensus could decrease the overexploitation and subsequently slow groundwater depletion. Scott added that solar energy is a valuable renewable resource that could both improve efficiency and reduce water use for energy production.
Scott mentioned some of the binational water management collaborations that have been implemented to date, including the Center of Excellence for Water Security16 and the Transboundary Aquifer Assessment Program.17 Institutions that are part of the North American Free Trade Agreement (NAFTA), including the Border Environmental Cooperation Commission and the North American Development Bank, have also been working towards a binational solution in this region. He added that the most effective type of transboundary collaboration will identify the challenges and look both within and beyond the scientific community to involve policy makers and stakeholders. Policy objectives can even be used to guide drylands research, he said.
Angelina Martínez Yrizar discussed her work as an ecologist in Sonora, Mexico, an area she has studied for 25 years. Sonora shares a very large border with Arizona, and the Sonoran Desert traverses the border and covers large parts of southern Arizona and California. Overall, the terrestrial ecosystems in Sonora are extremely varied: there are coastal regions, dry broadleaf forests, and temperate forests along the Sierra Madre mountain range. She noted that although Sonora makes up only 10 percent of Mexico’s total land area, it holds more than 20 percent of the country’s total flora—more than 4,500 total species. She said that due to land use changes, deforestation, and increased agricultural production, the biodiversity and functional integrity of Sonora’s ecosystems are being compromised. Changes to the landscape can ripple down from Sonora’s Arizona desert border to the coastal ecosystems near the Gulf of California.
Martínez Yrizar said she and her colleagues are concerned that as investment projects emerge between Arizona and Sonora, they seldom
15 See http://www.icid.org/wif2_full_papers/wif2_w.1.2.07.pdf [November 2018].
take into account the environmental consequences of the change. Mining, another growing industry in Sonora, has added to the state’s land and water pollution. And while not environmental changes, she said, drug trafficking and crime should also be considered for their effects on the political, social, and economic climates in the area. In addition to the anthropogenic changes, extreme climate events, such as droughts, heighten the region’s vulnerability to change. She closed with a passage from a study she and Alberto Búrquez did some years ago:18
The exploitation of minerals and industrial development have not been matched by strong measures to protect the environment. Especially lacking is the establishment of large nature reserves. The need for preserving natural areas has clashed with the desires of government and investors to develop large-scale mining, water-use projects, coastal tourism, fisheries, cattle ranching, and agriculture. The importance of nature reserves in preserving biodiversity, protecting upriver basins from erosion, providing recreation, keeping hydrological systems in balance, and reducing health risks have been only cursorily taken into account in government programs. (p. 312–313)
During the discussion in response to Scott’s presentation on sustainability challenges, Jurgen Schmandt (University of Texas at Austin) noted that there has been significant sediment loss in the Rio Grande and Rio Bravo reservoir storage areas because sediment is washed away with excess flood-waters when the storage gates are opened. He said that to his knowledge neither the United States nor Mexico has done research on or applied engineering efforts to this issue. Schmandt added that climate change-induced increased temperatures have caused more water flow down from mountainous snow pack areas. However, instead of adding to the water supply, the higher temperatures have led to increased evapotranspiration: the water is being absorbed back into the atmosphere. The water storage decreases have required innovations in agriculture and improved irrigation technology.
Schmandt elaborated on Minute 323 and noted that Minute 308 was also written to bolster drought management. He said he feels there are tremendous opportunities to expand the knowledge around and management of sustainability. Scott added that surface water storage, flow engineering, and infrastructure must increasingly be developed to augment underground storage and recovery for aquifers, which require particular recharge and pumping mechanisms. He said he thinks that the International Boundary
18 Búrquez, A., and Martínez Yrízar, A. (2000). El desarrollo económico y la conservación de los recursos naturales. In Sonora 2000: A Debate; Problemas y Soluciones, Riesgos y Oportunidades, Vol. I, Almada Bay. Mexico City: Ed. Cal y Arena.
and Water Commission and the 1944 treaty19 between the United States and Mexico are both examples of successful collaboration, but noted that the treaty is a 100-year treaty, and 2044 is not far off.
Jorge Morán Escamilla (El Colegio de San Luis) commented that while underground water is a valuable source, overexploitation of aquifer banks can result in subsidence (caving or sinking of the ground above). He said Los Angeles and parts of China have already experienced this phenomenon. Scott agreed that storing water underground when aquifers are already being overexploited seemed counterintuitive, and he rephrased Morán’s point into lay terms: if a person goes to the bank to make a deposit and finds that the bank is bankrupt, that person is not going to want to make investments in that bank. He added that whether or not the aquifers are recharged, it will be important to develop regulation schemes for the use of groundwater and surface reservoirs. Washington-Allen said that the lack of regulation on groundwater is a global concern that is becoming a rising topic in the scientific community.
Morán asked if the desalinization of water for use on protected agriculture would result in higher salt contents in soil and eventual desertification. Scott replied that protected agriculture does not necessarily lead to soil salinization, but that water is required to remove salts from the soil—the so-called leaching requirement of irrigation that is additional to the crop’s demand for water. He said this critically important use of water is often seen, mistakenly, as “inefficiency” because the plant itself does not consume the water.
Alvarez told the workshop participants about a water reuse case study conducted in Tijuana, Mexico, and a study being conducted in Los Alisos, a small Sonoran municipality, to recharge an aquifer with excess water from their water treatment plants. El Paso, Texas, is doing something similar, putting together an executive project to inject treated wastewater directly into its water network. He said that there are many projects like this occurring around the world and that researchers and policy makers need to stay on top of these developments and learn from them.
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