There is growing concern that a warming climate will alter water supplies in many regions. Determining the best course of management and adaptation is an important task for water managers. This study explores the impact of climate warming and differing treeplanting scenarios on water supplies (peak flow rates, times, and total water yield) in four forested mountain watersheds in Colorado, USA. Tree migration, disturbance, active management (treeplanting), and a changing climate were simulated with a spatially explicit, high-resolution hydrologic model. Disturbance and climate had considerable impacts: relative to current conditions, forest mortality increased water yield, primarily due to lower transpiration losses; peak flows occurred earlier (1–2 weeks); and winter baseflow rates were higher (2–5 times current rates). Planting had minimal effects on peak flow rates/timing and total water yield in some watersheds, but more in others. Simpler topography and low biodiversity were associated with higher sensitivities to vegetation/management choices: depending on the scenario, models predicted a 22 to 12% difference in peak flow rates coupled with a 10 to 117% range in total yield (between scenarios). Overall, certain systems are more sensitive to management than others, and we discuss ways to evaluate potential hydrologic sensitivity to disturbance and management in mountainous watersheds.
