The Intergovernmental Panel on Climate Change (IPCC) suggests that vulnerability to climate change depends on three main factors: exposure, sensitivity and adaptive capacity. Each factor was evaluated in a hydrologic context, for instance exposure was interpreted as a change in surface runoff. Factors were combined using a Geographic Information System (GIS) and an overall methodology to map hydrologic vulnerability was proposed. The Conchos River Basin, which is the main tributary of the Rio Grande, was used as a case study. The long-term rate of change in surface runoff was estimated considering the variation in future precipitation from 23 Atmosphere-Ocean General Circulation Models (AOGCM) by using the Reliability Ensemble Averaging (REA) method. Two climate change scenarios (A1B and A2) and three time horizons (2030, 2050 and 2100) were chosen. Results showed a decrease in surface runoff up to 28% (A1B-2100) north of the Basin. Hence, it is likely to have more frequent droughts. However, it would be challenging to compensate the lack of surface runoff since groundwater resources are already depleted. Finally, overall hydrologic vulnerability maps were obtained to locate the most vulnerable regions, where precisely adaption efforts would be more necessary to sustain environmental conditions.