Hydro-Economic Analysis of Water Supply for Baja California, Mexico

Abstract

This paper describes a hydro-economic analysis of agricultural, environmental and urban water supply alternatives for years 2025 and 2080, in Baja California. Alternatives include idealized water markets, wastewater reuse, seawater desalination and infrastructural expansions. A network of the water system was built to considering hydrology, agricultural, environmental and urban demands, infrastructure, economic values of water and operating costs. Wastewater reuse with other projected infrastructure expansions are overall the most economically optima alternatives. Markets offer leverage and flexibility for the future urban needs for locations with the proper infrastructure. Worthwhile expansions include a larger aqueduct to convey Colorado River water to the west. At current water price and operating costs, seawater desalination is uneconomical. Wastewater reuse for restoration is also an economic source of instream flows, with institutional arrangements on a subsidized water price. Hydro-economic analysis is useful to better understand water-related issues in Baja California and provide a technical basis for developing and comparing long-term water management solutions. Introduction The northern region of Baja California is likely to face in the next few decades, significant challenges to supply water for urban and agriculture demand and to maintain adequate ecosystem functions. Most of the water supplies are concentrated in the northeast of Baja California. The Mexican border cities of Tijuana-Rosarito, Tecate, and Mexicali mostly depend on surface water supplies from the Colorado River. About 200 of groundwater in the northeast are allocated for urban uses. Further South, the coastal city of Ensenada relies mostly on local aquifers to fulfill both agriculture and urban demands. Currently, cities in Baja California are increasing their water use relative to agricultural users. This trend does not seem to reverse. Therefore, economically optimal alternatives for future urban, environmental, and agricultural water supplies are needed. The Tijuana-Rosarito metropolitan area (Figure 1), dominates urban uses currently estimated in 105 MCM/yr, followed by Mexicali (86 MCM/yr). Most of this water is supplied via the Colorado River aqueduct with an annual capacity of 126 MCM/yr, which also delivers water to the city of Tecate . Ensenada, currently isolated from the border water supply system is about to claim its 8 MCM/yr share from the Colorado River system by means of a connection to the existing aqueduct near Tecate. Aquifers sustaining high value agriculture and urban uses in the Ensenada region are facing saline intrusion issues, due to groundwater overdraft (Daessle et al. 2006). However, the largest World Environmental and Water Resources Congress 2008 Ahupua'a © 2008 ASCE Copyright ASCE 2008 World Environmental and Water Resources Congress 2008: Ahupua'a 2 water user in the border is by far irrigated agriculture in the Mexicali Valley; which at least takes 2000 MCM/yr from surface and groundwater sources. Water instream flows to keep ecosystem functions in the Colorado River Delta (CRD) had not been a concern until two decades ago; however, scientists estimate that 40 MCM/yr of instream flows with pulse flows of 300 MCM/year every four years are required to keep healthy ecosystems in the CRD (Glenn et al. 2001). Nowadays the CRD has survived partly due to operational water releases from the US beyond the 1994 treaty quota for Mexico. These overflows are not expected in the years to come. Figure 1 The northern region of Baja California, Mexico (after Malinowski 2004). In the following decades, water management challenges for Baja California include: − Water supplies and wastewater management for the rapidly growing cities of Ensenada, Mexicali, Tecate and Tijuana-Rosarito − Institutional arrangements to oversee water transfers among agriculture, environmental and urban uses − Establishment of environmental water flows to sustain and enhance the ecosystem of the Colorado River Delta Even though, water resources management in the northern Baja California region has produced vast research, systematic analysis involving hydrology, economics, competing demands and infrastructure, remains unexplored. This paper provides insights on promising water supply alternatives for Baja California, thru a formal integrated quantitative analysis of water resources in the region. Analyzed water supply strategies include idealized water markets, infrastructure expansions, wastewater reuse, and seawater desalination. CALVIN (CALifornia Value Integrated Network), a network flow optimization model (Jenkins et al. 2001) was used to undertake this analysis. The Baja CALVIN model (http://cee.engr.ucdavis.edu/faculty/lund/BajaCALVIN) is a similar World Environmental and Water Resources Congress 2008 Ahupua'a © 2008 ASCE Copyright ASCE 2008 World Environmental and Water Resources Congress 2008: Ahupua'a 3 model of the water resources of northern Baja California. Scenarios hosting these alternatives consider hypothesized 2025 and 2080 levels of development. METHODS The Baja-CALVIN model offers a systematic approach to study complex water resource management problems. Studies using this modeling framework and approach include estimating economic potential of water markets, gains from conjunctive use operations, climatic change, infrastructure expansions, and conservation issues (Jenkins et al. 2001; Medellin-Azuara et al. 2007; Pulido-Velazquez et al. 2004; Tanaka et al. 2006). This study merges two subregional CALVIN models for Ensenada (Waller-Barrera 2008) and Mexicali (Medellin-Azuara et al. 2007) with a new network for the metropolitan area of Tijuana-Rosarito. Carrizo Reservoir Tijuana/Rosarito Residential Ensenada Urban Tijuana/Rosarito Non-Residential Maneadero Agriculture Guadalupe Agriculture La Mision Aquifer