Human Activity-Environment Interaction at the U.S.-Mexico Border

Craig Forster1 and Tjeerd Schaafsma2

Introduction

The Border+20 (B+20) Project is designed to develop a modeling framework for supporting interdisciplinary, binational decision-making along the 3,200 km U.S.-Mexico Border Region (Figure 1). The principal goal for this effort is derived from the vision statement generated at the first Border Institute convened by the Southwest Center for Environmental Research [1999]: to aid borderland decision-makers in finding ways to maintain a satisfactory quality of life for all residents and a healthy sustainable natural environment. To this end, the Border+20 Project is tasked with projecting future conditions along the U.S.-Mexico border for a series of alternative 20 year futures (hence the 20 in the project name Border+20).

As recommended by Kinsley et al. [2002] we use a systems thinking approach to map out key elements of the borderland human-environment system and to build system dynamics models that quantitatively represent complex linkages, flows, and feedbacks between and within system elements. The interdisciplinary B+20 Project Team comprises researchers from five U.S. universities involved in the Southwest Center for Environmental Research and Policy (SCERP) consortium (Arizona State University, New Mexico State University, San Diego State University, University of Texas at El Paso, University of Utah) and five Mexican academic institutions (Universidad Autónoma de Baja California, Universidad Autónoma de Ciudad Juárez, Instituto Tecnológico de Ciudad Juárez, Instituto Tecnológico y de Estudios Superiores de Monterrey, El Colegio de la Frontera Norte). Disciplinary expertise represented by the team members includes, but is not limited to: border studies, hydrology, air quality, energy supply/demand, water resources supply/demand, urban planning, psychology, economics, demography, sociology, ecology, earth science, human health and communication. Our goal is to provide a modeling framework for decision-making that will increase the likelihood for improved transborder cooperation and help lead to a sustainable future for those living along the U.S.-Mexico border.

Figure 1. U.S.-Mexico border (heavy black line) and neighboring Border States (gray) in the United States and Mexico.

A Brief Synopsis of the U.S.-Mexico Border Region

The 3,200 km long U.S.-Mexico Border Region (Figure 1) spans the North American continent with 15 principal, sister-city communities distributed along the border. County populations in the U.S. border region range up to 2.8 million people in west coast city of San Diego, U.S.A. with a total of 6.4 million people in the U.S. borderlands. The corresponding populations of Mexican ‘municipios’ (Mexican equivalent of U.S. counties) range up to 1.3 million people in the San Diego sister-city of Tijuana, Mexico with a total of 5.7 million people in the Mexican borderlands. Rapid population growth leads to projected 2020 populations of 9.0 million and 10.5 million U.S. and Mexico border residents, respectively [Peach and Williams, 2000]. Thus, the current total borderland population of about 12.1 million people is likely to increase by more than 60% to 19.5 million over the next 18 years. Most population growth will occur in the existing, transborder sister cities where intense interaction between human activity and the environment is concentrated. At the same time long, desolate stretches of desert between the principal sister-cities are essentially unpopulated, leading to significant difficulties in restricting the illegal flow of people and drugs from Mexico to the United States. The tremendous rate of population growth was initially caused by Mexican citizens migrating to work in the economically attractive border region. Relatively high fertility rates and relatively low death rates in this young population of migrants has led to a rapid natural population increase that would continue even if Mexican migration to the border were to end [Peach and Williams, 2000].

Geographic conditions vary substantially along the border with high, north-south oriented mountain ranges in the western border region separating border communities located at elevations ranging from sea level (at both coastal and inland communities) to 1,234 meters above sea level. In the east, community elevations are generally less than 300 m above sea level. The border region has a semi-arid to arid desert climate with precipitation ranging from less than 10 cm per year at some inland communities to 70 cm per year on the east coast. With the exception of the west coast communities of San Diego, U.S.A. and Tijuana, Mexico, annual average maximum temperatures are about 29 oC and average minimum temperatures about 16 oC. Cooler temperatures on the west coast yield an annual average maximum of 21 oC and an average minimum of 14 oC for San Diego, U.S.A. and Tijuana, Mexico. The specter of future natural and anthropogenic climate variability suggests that we should be concerned by the possibility that declining precipitation rates and increasing temperatures will cause additional stress on borderland water, energy, natural resources and ecosystems.

Economic growth stimulated by border attributes (e.g., attractive differentials in labor wage rate, enforcing of environmental laws, etc.) has been substantial since the 1940s [Peach and Williams, 2000]. In 1994, implementing the North American Free Trade Agreement (NAFTA) between Canada, the United States and Mexico further stimulated economic growth. Unfortunately, the conditions that stimulate economic growth at the border have yielded low per capita incomes and high unemployment rates when compared to those elsewhere in the U.S. Although per capita incomes in the Mexico border communities are much greater than those elsewhere in Mexico, Mexican border minimum wage rates are approximately 10% of that of their U.S. sister city counterparts [Peach and Williams, 2000]. High rates of economic and population growth, coupled with low incomes, have meant that many environmental problems have developed in the U.S.-Mexico border region because insufficient public financial resources exist to meet rapidly expanding infrastructure needs. The current U.S. economic recession, combined with increasing attractiveness of low labor wage rates in countries such as China, raises concerns that the borderland economic expansion of past decades may slow while the borderland population continues to grow. Economic stagnation in the border region would exacerbate current environmental problems and deteriorating human quality of life because access to the funding needed for infrastructure development will be further eroded.

Water availability and quality, air quality, human health, and ecosystem health are key elements of the borderland human-environment system suffering as a consequence of high population growth rates and rapidly expanding urban areas. In the arid climate of the border region there is increasing competition for the scarce water resources needed for human consumption, agricultural production, industrial activity and ecosystem health. Average per capita water use in the U.S. borderland (615 liters per capita per day) is about 41 % greater than that of the Mexico borderland (435 liters per capita per day) [Westerhoff, 2000]. Because water use is correlated to standard of living, efforts to improve the quality of life in the border region could lead to increased per capita rates of water use unless counteracting measures of efficient water conservation and recycling are introduced. Binational planning for efficient water use and system-wide wastewater treatment is required if sister-city communities are to develop a sustainable water supply future while also reducing the prevalence of water-borne disease.

Weakly enforced environmental regulations in Mexico border communities are allowing excessive air pollution that, in turn, causes the air quality in several sister-cities to exceed U.S. national standards; despite relatively low emissions in the U.S. sister cities. Imaginative approaches are needed to develop cost-effective reductions in the binational air emissions that impact quality of life and human health on both sides of the border. Natural ecosystems in the borderland desert environment have been severely punished by human activity. Yet, in many cases well-managed desert ecosystems can provide cost-effective solutions to water supply challenges encountered in human communities [Committee on Sustainable Water Supplies for the Middle East, 1999]. For example, water supply development has eliminated many natural riparian areas that at one time provided natural water treatment in addition to habitat for indigenous flora and fauna. However, artificial wetlands recently constructed in the U.S. Imperial Valley region are helping to remove the suspended solids introduced to surface water by the irrigation runoff associated with agricultural activity. We expect that our systems thinking and modeling approach will assist in evaluating the relative merits of various options proposed to mitigate the degradation of natural systems in the borderland and improve the quality of life for people living in the U.S.-Mexico border region.

A Systems View of the U.S.-Mexico Border

The principal elements of a binational, human-environment system model are shown in Figure 2. Population and economic growth drive change in a borderland community. Ultimately, changes in both the economy and population are influenced by the way that border inhabitants respond to concerns regarding human health and other aspects of quality of life. At the same time, quality of life is strongly influenced by the changes in land use, transportation, energy, water supply, air quality and ecosystem services that are driven, in turn, by changes in population and economic activity. Each model element shown in Figure 2 represents the processes operating on both sides of the border. The detailed system model structure, however, explicitly distinguishes between processes operating on each side of the border and the processes that cause the transfer of ‘stuff’ across the border. An important contribution of the systems approach is that we explicitly account for the linkages, feedbacks and interactions across the border that are often not fully considered by decision-makers working independently on each side of the border.

‘Stuff’ flowing within the border region includes water (good and poor quality), air (polluted and otherwise), disease, money, products (food, agricultural, commercial, manufacturing, entertainment, etc.), waste products, social capital, services, electricity, fuels, vehicles, light, sound, ideas, community spirit, flora and fauna. In many cases, human activity at the border restricts flow of ‘stuff’ across the border with the most active restrictions occurring at the ports of entry found in sister-city communities. Notable exceptions include the transborder movement of groundwater in binational aquifers, migration of air pollution in transborder airsheds and the movement of indigenous flora and fauna within and through regional ecosystems. The movement of other ‘stuff’, however, is restricted by the physical, economic, legal and spiritual presence of the border.

Figure 2. Overview of the elements of a borderland system model of human activity and the natural environment. Although additional arrows are not shown for the sake of clarity, all elements within the shaded circle interact with one another to varying degrees.

A thought experiment proposed by the B+20 project team asks: “How might the borderland human-environmental system change if all restrictions on transborder flows were removed?”. Once this scenario is thoroughly mapped then it would be valuable to compare it to one where all flows that can be controlled are severely restricted. Several different outcomes could be envisioned for each scenario. It is hoped that such an exercise would help to define a mix of binational policies that would lead to a sustainable future for borderland inhabitants. For example, removing all restrictions on human migration across the border is expected to cause massive movement of Mexican citizens to the U.S. Although one should expect an initial period of enhanced migration, people will only migrate across the border as long as conditions in the new location are clearly preferable to those in their home community. As people move from place to place their behavior modifies the demographic and economic conditions at each location while consuming natural resources. At the same time, ties to one’s home community are difficult to break – perhaps even more difficult when it is easy to travel home frequently in the absence of border restrictions. Thus, it seems reasonable to expect that an equilibrium population distribution should result. In the absence of performing a quantitative, multifaceted calculation, however, it is difficult to guess when such an equilibrium condition might be reached and how the total population of Mexican nationals might be distributed between the two countries.
Furthermore, it is unclear whether net economic impacts on the two nations would be positive or negative when equilibrium is attained. At this stage in the B+20 project, however, we are focused on more localized geographic targets with smaller-scale questions aimed at better informing decision-making in specific sister-city communities.

Figure 3 shows the three sister-city border communities to be considered in our current model development activity; El Paso (U.S.A.)/Ciudad Juárez (Mexico), Calexico (U.S.A.)/Mexicali (Mexico) and San Diego (U.S.A.)/Tijuana (Mexico). Although all three locations have a similar set of underlying conditions (climate, borderland economic drivers, population drivers, etc.) social, economic, natural resources and geographic differences dictate that separate models be constructed for each sister-city community. To date our model development effort has focused on El Paso/Ciudad Juárez. We recently expanded our effort to develop a separate model to explore complex water-supported ecosystems in the Salton Sea, California near Calexico/Mexicali (Figure 3). As this work expands, we will move progressively westward to develop a Baja California model that contains the sister-city communities of Calexico/Mexicali and San Diego/Tijuana in order to explore how to satisfy increasing San Diego/Tijuana demands for water and energy from the regions shown in Figure 3.

The El Paso/Ciudad Juárez System Model

Although it is beyond the scope of this brief statement to outline the details of the El Paso/Ciudad Juárez system model, a brief outline of several key model sectors should help illustrate how we are proceeding. Two key questions have been defined to help frame the development of the model sectors:

Question 1 - Given the various state and national water management agencies involved in supplying water from common sources to urban communities and agriculturalists, what changes in agency policies and approaches might be effected to increase the likelihood for achieving water sustainability and satisfactory quality of life for borderland residents?

Question 2 - Given transborder disparities in minimum wages and household income, what policies might be effected to increase the likelihood for providing a healthy economy and satisfactory quality of life for borderland residents?

A principal emphasis in our effort to assure a satisfactory quality of life for border inhabitants involves assessing how human health along the border is affected by changes to the human-environmental system captured in Figure 2 and vice versa.

Attempting to answer the above questions has led us to develop a system model with a subset of the elements shown in Figure 2. These elements include the all-important population, economy and quality of life sectors combined with land use, transportation, water supply and air quality sectors (Figure 4). The foundation for each sector is briefly described in the following paragraphs.

Figure 3. Current Border+20 geographic, sister-city targets (circles) and U.S. and Mexico Border States (shaded). System dynamics models are being constructed for each sister-city context.

Population & Economy Sectors:

Both national and local scale binational population and economy sectors are contained in the system model because national-scale population growth, in part, fuels change in both national economies that, in turn, influences borderland sister-city economies. A simplified view of the population and economy interactions at the national level is shown in the causal loop diagram of Figure 5. Underlying assumptions include the following:

1. Changes in the U.S. economy have a strong impact on Mexico’s economy and unemployment rate, but not vice versa,

2. Estimates of national unemployment rate and economic productivity per worker are key factors controlling the national Gross Domestic Product (GDP) of both the U.S. and Mexico, and

3. Migration of Mexican nationals to the U.S. is largely driven by a differential in GDP between the two countries.

The (+) and (-) signs noted at the heads of each arrow shown in Figure 5 indicate whether an increase in the source parameter causes an increase (+) or decrease (-) in the target parameter. For example, because growth in the U.S. national GDP is typically greater than that of Mexico’s GDP, increasing U.S. GDP leads to an enhanced binational economic differential that helps to drive the migration of Mexican nationals to the U.S. At the same time, growth in Mexico’s GDP helps to close the gap and reduce the binational economic differential. Assigning values and relationships within the model that are appropriate to the region produces plausible, national-scale economic and population projections that include a sporadic cycle of economic recessions that mimics that of past recessionary cycles. For example, the population of El Paso is projected to grow from 0.76 million in 2000 to 1.1 million people in 2020 while the population of Ciudad Juárez is projected to grow from 1.2 to 2.4 million people over the same time period [Peach and Williams, 2000].

Figure 4. Overview of the elements of a borderland system model of human activity and the natural environment for the El Paso/Ciudad Juárez region distilled from that of Figure 2. Although additional arrows are not shown for the sake of clarity, all elements within the shaded circle interact with one another to varying degrees.