Final Report: Water and Sustainable Development in the Binational Lower Rio Grande/Bravo Basin

EPA Grant Number: R824799
Title: Water and Sustainable Development in the Binational Lower Rio Grande/Bravo Basin
Investigators: Schmandt, Jurgen , Aguilar, Ismael , Armstrong, Neal , Chapa, Liliana , Contreras, Salvador , Edwards, Robert , Hazelton, Jared , Jesus Navar, Jose de , Mathis, Mitchell , Vogel, Enrique , Ward, George
Institution: Houston Advanced Research Center , Texas A & M University , The University of Texas at Austin
EPA Project Officer: Hiscock, Michael
Project Period: November 1, 1995 through January 1, 1998
Project Amount: $400,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water


The Houston Advanced Research Center (HARC) and the Instituto Tecnologico y de Estudios Superiores de Monterrey (ITESM) conducted an integrated assessment of water resources, development, and the environment in the rapidly growing, economically strategic Lower Rio Grande/Rio Bravo Basin. At the heart of the project was a fundamental question: Will there be enough water, of acceptable quality, to support future growth in the drought-prone, ecologically fragile region? The project had three objectives: (1) develop comparable data sets on water and development from both Mexican and U.S. sources, (2) analyze water resource and management issues as critical factors for the region's long-term development, and (3) identify options for water management that could lead to a sustainable path of regional development.

To carry out the project, task force members from Northern Mexico and Texas were organized into six binational teams: (1) water supply and demand, (2) water quality, (3) population, (4) regional economic development, (5) ecology, and (6) water management. In general, data available by 1995 were used. Hydrological data for the current prolonged drought were not yet available.

We divided the study region into a large hydrological region and a smaller impact region. The hydrological region encompasses the watershed of the Lower Rio Grande from Fort Quitman, TX (about 80 miles downstream from El Paso, TX) to the Gulf of Mexico, a distance of about 800 miles. Year-round stream flow in the Lower Rio Grande is ensured by two tributaries?the Rio Conchos (Mexico), which accounts on average for two-thirds of this flow, and the Pecos River (New Mexico-Texas), which accounts for one-third. In 1944, Mexico and the United States reached agreement on the division of waters in the Lower Rio Grande. The Treaty of 1944 gave the United States rights to part of Rio Conchos water. In exchange, Mexico received water rights in the Colorado River further west on the international border. The Treaty also provided for the construction and management, by the two countries, of two large reservoirs on the Lower Rio Grande. Falcon Reservoir was completed in the early 1950s and Amistad Reservoir was completed 15 years later. Since 1972, the two reservoirs have been operated as a single system. The reservoirs provide 95 percent of available surface water to areas downstream. The remainder comes from smaller Mexican tributaries, runoff from precipitation, and return flows from irrigation.

The impact region encompasses the last 270 river miles (434 km) downstream from Falcon Reservoir and a 30 to 40 mile strip of land on either side of the river. This land is fertile, and irrigated agriculture has been a part of the regional economy since before 1900. For part of our analysis, we also considered the Monterrey metropolitan area (MMA), Nuevo Leon, and the twin cities of Laredo, TX/Nuevo Laredo, Tamaulipas. Monterrey, Mexico's second largest industrial center, has strong hydrological, economic, and cultural ties to the immediate impact region. Laredo/Nuevo Laredo are the largest twin cities on the Rio Grande between the Amistad and Falcon Reservoirs, and they receive their water from the Rio Grande.

We coped with the complex geography of the region and the disconnect between natural and political boundaries by adopting the following conventions: our hydrological region is the Lower Rio Grande Basin. We named the impact region the Lower Rio Grande Border Region (LRGB). We call the Mexican portion of the impact region the Tamaulipas Border Region (TBR), and we call the Texas portion of the LRGB, following local custom, the Lower Rio Grande Valley (TV).

The project examined water and development under current and projected future conditions. The "current analysis" sought to gather and integrate information and data to understand today's linkages between population growth, water supply and use, the regional economy, water quality, and the ecosystem. The "future analysis" examined water and development to the year 2030 and used the following four plausible future scenarios of water scarcity:

  1. Drought-of-Record?establishes a "baseline" scenario using the 1945-1960 hydrology (including the drought-of-record years).
  2. Full Conchos Development?The average inflow into the Rio Grande/Bravo from the Rio Conchos, a major tributary in Mexico, has been much greater than the amount required by treaty. This scenario is based on the possibility that, in the future, Mexico will utilize all Conchos water except the Treaty amount.
  3. Superdrought?Removes a single, isolated anomalous weather event (Tropical Storm Alice) that occurred during drought of record from the 1945-1960 hydrological data to create a more likely representation of the "worst possible drought."
  4. Worst Case?Full Conchos Development and Superdrought scenarios combined.

Summary/Accomplishments (Outputs/Outcomes):

Population. The LRGB has experienced rapid population growth since the 1950s. From 1950 to 1995, the population rose from 680,203 to 2,146,601?an increase of 216 percent. Much of the increase is the result of in-migration from the interior of Mexico. This trend is likely to continue into the future. The total population in 2030 is estimated to rise to 4.9 million?2.6 million in the TBR and 2.3 million in the TV. Between 2000 and 2030, the number of people living in the impact region will double. Doubled population also is projected for the MMA. The population of the entire basin, including Monterrey and Laredo/Nuevo Laredo, will grow from 5.1 to 11.1 million.

Regional Economic Development. In the Mexican TBR, the largest economic sectors are services, commerce, and manufacturing. Agriculture has declined from 15 percent of total output in 1970 to 10 percent in 1993. Maquiladoras represent 12 percent of all companies in the state of Tamaulipas. Maquiladora activities are heavily concentrated in the northern part of the state, specifically in Matamoros, Reynosa, and Nuevo Laredo, which are key manufacturing centers not only in Tamaulipas but also for the whole of Mexico. Tamaulipas and neighboring Nuevo Leon are together the second most important destination for foreign direct investment in the country.

In Texas the border counties have experienced rapid growth in personal income in recent years. Even so, they still have the lowest per capita income both within Texas and the United States. In 1994, average per capita income ranged from $6,583 in Starr County to $11, 346 in Cameron County. This compares with a per capita personal income of $19,716 for Texas and $21,696 for the United States. Historically, irrigated agriculture has played an important role in the development of the TV. Yet the share of total earnings from farm income and related services has declined to around 3 percent currently in all counties except Willacy where it remains at 31 percent. Cross-border trade is the single most important industry representing 20 percent or more of total earnings. Services and public sector spending are strong, while manufacturing is less important. Unemployment in the border region has been high, but the region has enjoyed solid economic growth throughout the 1990s. This upward trend was slowed, however, by the 1994 devaluation of the peso and the ensuing recession in Mexico.

Irrigated Agriculture. Both the TBR and the TV are important suppliers of fruits and vegetables, as well as corn and sorghum. In 1996/97, notwithstanding the ongoing drought in the Lower Rio Grande Basin, the TBR was responsible for 17 percent of Mexico's agricultural production. Irrigation district 025, Lower Rio Bravo, is the principal producer with a total area of 236,735 ha. Four of the district's six units (210,362 ha) receive Rio Bravo water through the Anzalduas diversion channel, and the remaining two units pump water directly from the Rio Bravo. The amount of irrigated land varies greatly from year to year depending on water availability and several other factors. In 1981, for example, only 140,000 ha were irrigated. Between 1980 and 1993, the size of irrigated land declined by 1,400 ha each year. Annual water deliveries reached an all time high of 1,900 Mm3 in 1989 but plunged to 382 Mm3 in 1996 due to drought. Irrigation district 026, Lower San Juan, is second in importance. In this district, 86,097 ha were irrigated during the best years (1970s); 76,602 ha receive water from the Rio San Juan. The remainder is irrigated by water from the Rio Bravo. Due to drought and water disputes with MMA, the irrigated area during most of the 1990s was less than 40,000 ha, only one-third of the total available acreage in 1998.

In Texas, farmers are organized in 28 irrigation districts. All districts pump water directly from the Rio Grande. Because groundwater is brackish, only a small amount is used for irrigation. According to International Boundary and Water Commission (IBWC) statistics, irrigated land on the U.S. side of the Lower Rio Grande Basin declined from 300,000 ha in 1980 to 288,000 ha in 1993. The U.S. Census of Agriculture reports a much steeper 44 percent decline in irrigated land between 1982 (657,750 acres) and 1992 (366,656 acres). During the same time, the market value per acre of land in the TV declined by 23 percent. Our field analysis shows that the agricultural sector in Texas, in some cases, can compensate for reductions in water by crop selection, better technology, and reduction in water losses. One irrigation district used 40 percent less water due to irrigation improvements, without economic loss. The same district did better than its neighbors when water supply was diminished during the current drought. Modeling of the agricultural response to 20 and 40 percent reduction of irrigation water showed adoption of more efficient irrigation technologies, changed cropping patterns, and minimal overall impact on the TV economy.

Water Supply and Use. Releases from Amistad-Falcon account for 95 percent of the water supply to the LRGB. The river channel serves as the conduit for delivery. Water diverted to users in Mexico and Texas reduces flow in the channel. The total flow in the channel diminishes from an average below Falcon of 258 Mm3/month to a flow at Brownsville of 51 Mm3/month. As a result, the river loses part of its ability to dilute wastewater discharged in the river, to extrude salinity intruding up the channel from the Gulf of Mexico, and to maintain ecosystems in and along the river. Mexico diverts its water mainly at a single point, the Anzalduas canal. Water in Texas is diverted at numerous pump stations. From 1980-1993 average monthly Mexican diversion was 115 Mm3. This is nearly equal to the United States diversion of around 113 Mm3/month.

During the first 18 years of joint operation of Amistad-Falcon reservoirs (1972-1990) average monthly delivery was 202 Mm3. During the period (1945-1960) that includes the drought of record, we calculated the firm yield of the system, defined as constant delivery to the point of zero storage, to be about 232 Mm3.

Using models of the river hydrology and the tandem operation of the Falcon-Amistad reservoir system, we estimated the firm yield of this system under the four scenarios of future water availability described above. The results, which account for increased water consumption between Falcon and Amistad due to population growth since 1960, are summarized in the following table:

Firm Yield for Amistad-Falcon System Under Indicated Scenarios (Mm3/month)
Full Conchos
Worst Case

The Full Conchos Development scenario has the single largest impact on firm yield of the reservoir system, resulting in a 23 percent reduction compared with the historical hydrology. The Superdrought accounts for a 13 percent reduction in firm yield, while the Worst Case scenario, combining Full Conchos Development and Superdrought, results in a 31 percent reduction.

Projected Municipal and Industrial Water Demand (Mm3/month)

Municipal and industrial (M&I) demand was estimated to reach 45 Mm3/month by 2030, representing about 20 percent of firm yield under the historical hydrology scenario, and 28 percent under the worst case scenario. At present, M&I uses 12 percent. Using different assumptions about future per capita water use in Mexico, considerably higher M&I demand for TBR is possible, increasing from 16 Mm3/month in 1997 to 23 Mm3/month in 2030. In this case, the M&I share under the same scenarios will rise to 23 percent and 34 percent, respectively.

At present, agriculture uses 80 to 85 percent of available surface water. Irrigation use varies greatly from year to year. During 1980-1994 (just before major reductions in the delivery of water due to the current drought occurred), the combined average of Mexican and United States irrigation use was approximately 3,000 Mm3/year or 250 Mm3/month. Assuming that municipal and industrial water demand takes priority over irrigation and that the remaining volume of water is allocated to irrigation, we calculated the annual irrigation shortfalls under each future water availability scenario. By 2030, these shortfalls could reach 55 percent under the worst case scenario. Part of the shortfall will be met by declining water use by agriculture due to the conversion of land from agricultural to urban uses as well as market changes. The Texas Water Development Board estimates that irrigation demand will decline by 10 percent between 2000 and 2030. We conclude that larger reductions in agricultural use are likely both in Mexico and in Texas. Such reductions would be consistent with the existing trend of declining irrigated land on both sides of the border.

Water Quality. According to existing data, the Lower Rio Grande generally exhibits acceptable water quality for most constituents, relative to current standards. However, there is cause for some concern. High levels of total dissolved solids are often present in the river. This appears to be more due to natural brines originating in the Pecos River than to point or nonpoint source loads within the Lower Rio Grande Basin. During periods of low flow, the concentration of dissolved solids and other pollutants increases dramatically. The frequency of low flow periods, and therefore of poor water quality, will likely increase in the future, limiting its use of water for agricultural irrigation as well as municipal and industrial uses. Examination of dissolved oxygen (BOD) under the future water availability scenarios showed that the quality standard for BOD would likely not be met under such reduced flow conditions. High levels of fecal coliforms also occur and there is some evidence of elevated concentrations of other pollutants immediately downstream of population centers.

Ecosystem. Nearly 700 species of wildlife have been documented in the study area. More than 86 vertebrate species are listed as endangered or threatened or are considered candidates for immediate protection. Using fish communities as an indicator of ecological health, the study found that major alterations to the riparian ecosystem have occurred steadily over the course of the last century. The river from Falcon to Brownsville-Matamoros has lost many of its freshwater species. Instead, exotic or estuarine and even marine species are found. This trend is particularly pronounced near the mouth of the river. These faunal changes appear to be correlated with decreasing stream flows, the proliferation of exotic species, and increases in chemical pollution. An index of biological integrity was developed for the riverine ecosystem. The resulting ratings are poor for most locations, except Falcon Reservoir. Habitat destruction, decreased stream flow, and pollution appear to be the main culprits. Stream flow requirements for a healthy river ecosystem downstream from Falcon are not met today and will likely decline further without changes in water allocation.

Water Management. At the international level, reservoir management is conducted professionally and harmoniously between Mexico and the United States. However, different water laws and institutions in Mexico and the United States make cooperation difficult for issues that do not fall under the authority of the International Boundary and Water Commission. This gap is particularly serious in the areas of water planning and ecological protection. In the wake of the NAFTA agreement, cooperation between Mexico and the United States on improving river quality has increased. Major results of improving water treatment infrastructure already are visible, and more treatment plants will come on line in the next few years. Similar efforts are urgently needed to conduct cross border water planning and ecological restoration. The region also must develop institutional capacity to resolve conflicts between water users?between Mexico and the United States, between cities and agriculture, between development and ecological health.

Overall Conclusion. Whether the Lower Rio Grande/Rio Bravo Basin moves toward a more sustainable future concerning its water resources is largely a question of management. How can this shared resource best be used for the benefit of human populations on each side of the river and the region's uniquely diverse ecosystems? Potentially, there can be enough water, of acceptable quality, to support the water needs of 4.9 million people in the immediate impact area. To make this possible, agricultural use of water will have to be reduced significantly. Market mechanisms and mutually beneficial arrangements between cities and irrigation districts can bring about more efficient water use, making the rural-urban reallocation one of cooperation rather than conflict. However, without changes in allocative mechanisms to reflect minimum ecological water needs, not enough water will be left instream to maintain the ecosystem. As new wastewater treatment plants continue to come on line, water quality in the river may improve, although these improvements could be offset by increased concentration of pollutants due to decreased stream flow caused by increased use. The complex array of local, state, regional, federal, and international institutions involved in water management presents a formidable challenge, yet greater institutional cooperation and improved region-wide water management will be fundamental to maneuvering the Lower Rio Grande/Rio Bravo Basin toward a more sustainable future.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other project views: All 13 publications 3 publications in selected types All 2 journal articles
Type Citation Project Document Sources
Journal Article Aguilar BI. Interregional transfer of water in Northeastern Mexico: the dispute over El Cuchillo Dam. Natural Resources Journal 1999;39(1):65-98. R824799 (Final)
  • Abstract: Social Science Research Network
  • Journal Article Mathis ML. Using new approaches to environmental decision-making: an application of integrated assessment methods to water resource issues in the binational Lower Rio Grande Basin. Review of Policy Research 1999;16(3-4):138-167. R824799 (Final)
  • Abstract: Wiley InterScience
  • Supplemental Keywords:

    water, sustainable development, Mexico, United States, Texas, TX, Border Region, integrated assessment, water management., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Water & Watershed, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Economics, Ecology and Ecosystems, EPA Region, Social Science, Watersheds, risk assessment, water resources, Texas, climate change, Rio Grande Basin, (TX), availability of water resources, Region 6, aquatic ecosystems, water quality, watershed sustainablility, public policy

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    Original Abstract
  • 1996
  • 1997