Between 1992 and 2005, Chihuahua's Río Conchos outflows were at less than 10 percent of their historical average, prompting a highly public dispute with the U.S. over water quantity under terms of the 1944 U.S.-Mexico Water Treaty. Still, Mexico made a number of water "payments" and achieved an eventual resolution of the dispute. The resolution focused on a number of steps, including investing over $140 million in irrigation district water conservation projects in the Río Conchos, which has historically provided two-thirds of the Río Grande's water below Fort Quitman. Utilizing a case study approach rooted in political and cultural ecology, the research examines the factors -- from drought to land use change-- purported by different interest groups as contributing to the transboundary Texas-Mexico water dispute and finds at least three major "narratives" emerged in the period to explain the low flows, including drought, dam management and agricultural expansion and land use changes. The dissertation shows, however, that the reduced outflows and reductions in "dam" water to farmers was just one factor in a changing agricultural context in which new land tenure rules, decentralization of water management and the enactment of a more open economic framework precipitated resource use changes within the agricultural areas. In addition, the dissertation examines water and land resource use, including conservation projects, in three specific agricultural areas, and finds significant transformations in markets, policies and climate. Farmers were not just passive victims of reduced water use, the curtailment of government programs, and "privatization" of land and water resources, but adopted alternative water source strategies, began to examine more "conservationist-minded" agricultural practices and shifted cultivation to higher yield crops. Still, many farmers chose to abandon agriculture altogether, as there was some consolidation of resources among wealthier farmers. The "transnationalization" of the Río Conchos which has resulted from the new focus on its water users may influence local decision-making, but the research contends that resource management decisions in the Río Conchos Watershed are influenced and determined by local practices and environments as well as by economic and legal changes brought about by Mexico's inclusion into a globalized economy. / text

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Water resources availability could be affected by alterations of hydrologic processes as a result of climate change. Global projections of climate change indicate negative impacts on water systems with increasing flooding and drought events. This investigation presents the modeling of climate change effects on the hydrology and water resources availability in the Rio Conchos basin, the main tributary of the lower portion of the bi-national Rio Grande/Bravo basin, and its impact on the water treaty signed between the United States of America and Mexico in 1944. One of the problems most relevant to the study basin is the frequent occurrence of long drought periods. Coupled with increased water demands and low irrigation efficiencies, the competition for water resources is high on both sides of the border. Three main parts are addressed in this research. First, a hydrologic model has been developed using the one-dimensional, 2 layer soil moisture accounting scheme embedded in a water evaluation and planning model. Second, downscaled precipitation and temperature data, from five general circulation models for two emission scenarios, A1B and A2, were used as inputs to the Rio Conchos hydrologic model to determine the effect on basin hydrology. A multi-model ensemble is developed and several techniques, such as probability density functions, wavelet analysis, and trend analysis, are used to assess the impacts. Third, a water resources planning model for the basin has been developed, which integrates the hydrologic model and water management modeling, to evaluate the impacts on the entire water system and simulate adaptive strategies to mitigate climate change in the study basin. Skill-weighted multi-model ensemble results show that annual average runoff may be reduced by 12% ± 53% and 20% ± 45% in 2080-2099 relative to 1980-1999 for the A1B and A2 scenarios, respectively. Likewise, results show that reliability and resiliency of the water system will tend to decrease; consequently, the vulnerability of the system increases over time. Proposed adaptation measures could make the system more reliable and less vulnerable in meeting water demands for irrigation and municipal uses. / text