Abstract only available. The Conchos River Basin is one of the most important river systems in northern Mexico, and the most important tributary of the Lower Río Bravo/Rio Grande. The Conchos contributes approximately 2/3 of the total inflows to the Lower Rio Bravo/Rio Grande. As such, the flows are subject to the 1944 International Treaty between the United States and Mexico. Irrigation is the largest consumptive use in the basin, followed by industrial and municipal use. In addition there are flows required to satisfy the treaty. The region had a significant population growth in the last two decades, which combined with a severe drought in the 1990s, significantly impacted management of the water resources in the basin. The flows are regulated by a system of multiple reservoirs, one of them as large as Elephant Butte. In this work, an optimal water resources policy management is developed for a complex multi-reservoir system in a semi-arid region like the Conchos. The policy is adjusted for current climate conditions. To analyze its resiliency, this policy is simulated under predicted climate change scenarios. Using the MAGICC software package, variations in mean precipitation and temperature are estimated for several GCMs models, with different greenhouse emission scenarios, and for the following time horizons: 2025, 2050 and 2100. For each time horizon, the probability of variation in precipitation and temperature are estimated. The study evaluates the resilience of the current optimal policy to predicted climate changes. It also analyzes the adaptability of the policies as a function of the rate of climate change, allowing the quantification of the vulnerability of the system. Copyright ASCE 2005.