Efficiency, equity, and sustainability in a water quantity-quality optimization model in the Rio Grande basin

Integrated hydrologic and economic optimization models at the basin scale provide a framework for policy design, implementation, and evaluation in water-stressed basins. Despite the considerable potential that basin scale analysis offers, few basin-wide studies have examined tradeoffs among efficiency, equity, and sustainability when analyzing the design of water resource programs. This paper develops a basin scale framework to identify hydrologic and economic impacts of alternative water pricing programs that comply with environmental regulations for protecting water quality. Key issues are examined that confront integrated hydroeconomic basin models: linking water and economics, spatial and temporal scale integration, and quantity-quality relationships. Economic efficiency is defined and measured for each of two urban water pricing arrangements that comply with urban water quality protection regulations. Alternative measures of equity are analyzed in both spatial and temporal dimensions. Sustainability is evaluated physically for protecting the water supply and financially for long-term revenue viability. The approach is illustrated from results of a dynamic nonlinear programming optimization model of water use in North America's Rio Grande basin. The model optimizes the net present value of the basin's total economic benefits subject to constraints on equity, sustainability, hydrology, and institutions. It is applied to assess impacts of a two-tiered pricing program that complies with recently implemented drinking water quality standards for the basin's two largest U.S. cities: Albuquerque, New Mexico, and El Paso, Texas. Results suggest that two-tiered pricing of urban water supply has considerable potential to perform well in meeting the aims of efficiency, equity, and sustainability. Findings provide a general framework for designing water pricing programs that comply with environmental regulations.