Integrated hydrologic-economic-institutional water model for the Rio Yaqui basin, Sonora, Mexico

The development of appropriate tools that direct water resources management practices towards sustainability, while improving economic efficiency, requires the integration of several multidisciplinary components into a coherent analytical framework. Integrated Water Resources Models (IWRMs) are tools that integrate technical, economic, environmental, social, and institutional aspects to determine optimal water allocation among competing sectors at the basin level. IWRMs, which are particularly useful for regions with intense water competition, allows for the simulation and assessment of alternative policies and strategies on water resources management.;In this project, an integrated hydrologic-economic-institutional water model is created for a semi-arid basin, located in northwest Mexico, known as the Rio Yaqui basin, where water quantity problems are numerous. These problems include water scarcity, increasing demand for water, and poor water management practices. A rainfall-runoff-storage model is created and calibrated on a monthly basis by solving a water balance that reproduces the current water allocation. The rainfall-runoff model was capable of matching historical runoff records, except in the southern portion of the basin. In order to assess the impacts on the water resources of the basin, climate change and variability are incorporated into the surface water model. Storage estimates obtained from the incorporation of changes in precipitation rates show that the basin could suffer from water shortages during some years depending on the Global Climate Model (GCM) or the scenario used. Climate variability is assessed by fitting an autoregressive moving average (ARMA) model to a historical record of precipitation. According to the results, there is a significant probability that the storage of the reservoirs will fall below current water needs producing a strain upon the water resources of the basin. The rainfall-runoff model is coupled with a groundwater model of the Yaqui Valley through leakage from canals that deliver irrigation water from the surface water storage system to the Valley.;The hydrologic models are coupled with economic models that valuate the most relevant activities in the basin such as agriculture, residential uses, and the environment. According to the results, one of the least profitable crops in the Valley based on the amount of water used is wheat, which is also one of the most important crops and covers about 70% of the Valley. Reconverting the Valley to more profitable crops seems crucial based purely on economics. The sensitivity of the agriculture value is examined by modifying some model parameters including groundwater extraction rates, agricultural costs, and crop prices. High groundwater extraction rates generate a higher economic value, but also a significant decrease in the aquifer's storage.;Finally, a hypothetical water market is created to test different water allocations strategies. In this market, the implications of increases in residential water use and allocation of water flows for environmental purposes are analyzed. The results show that in order to maximize economic benefits, residential users should be satisfied before any other users. Additionally, including flows for environmental purposes could be optimal from an economic efficiency standpoint, because the total economic benefit generated within the basin per year is higher with environmental values included than the results obtained by considering only agricultural uses.