Water Resources Sustainability in Northwest Mexico: Analysis of Regional Infrastructure Plans under Historical and Climate Change Scenarios

The arid state of Sonora, Mexico, has embarked on a large water infrastructure project to provide additional water supply and improved sanitation to the growing capital of Hermosillo. The main component of the Sonora SI project involves an interbasin transfer from rural to urban water users that has generated conflicts over water among different social sectors. Through interactions with regional stakeholders from agricultural and water management agencies, we ascertained the need for a long-term assessment of the water resources of one of the system components, the Sonora River Basin (SRB). A semi-distributed, daily watershed model that includes current and proposed reservoir infrastructure was applied to the SRB. This simulation framework allowed us to explore alternative scenarios of water supply from the SRB to Hermosillo under historical (1980-2010) and future (2031-2040) periods that include the impact of climate change. We compared three precipitation forcing scenarios for the historical period: (1) a network of ground observations from Mexican water agencies; (2) gridded fields from the North America Land Data Assimilation System (NLDAS) at 12 km resolution; and (3) gridded fields from the Weather Research and Forecasting (WRF) model at 10 km resolution. These were compared to daily historical observations at two stream gauging stations and two reservoirs to generate confidence in the simulation tools. We then tested the impact of climate change through the use of the A2 emissions scenario and HadCM3 boundary forcing on the WRF simulations of a future period. Our analysis is focused on the combined impact of existing and proposed reservoir infrastructure at two new sites on the water supply management in the SRB under historical and future climate conditions. We also explore the impact of climate variability and change on the bimodal precipitation pattern from winter frontal storms and the summertime North American monsoon and its consequences on water management. Our results are presented in the form of flow duration, reliability and exceedence frequency curves that are commonly used in the water management agencies. Through this effort, we anticipate to build confidence among regional stakeholders in utilizing hydrological models in the development of water infrastructure plans and to foster conversations that address water sustainability issues.