Dwindling Groundwater Reserves Will Threaten Mountain Streamflow in a Warmer World

Abstract

Groundwater storage and release in mountain systems is often ignored compounding uncertainty in how these systems may respond to climate change. To assess the importance of groundwater to mountain streamflow, we combine an extensive data network with a high-resolution, integrated hydrologic model stretching into the deep subsurface for a Colorado River headwater basin. In a warmer climate, increased forest water use reduces recharge, thereby destabilizing groundwater storage such that it cannot recover to historical levels even during simulated wet periods. Groundwater depletion significantly reduces average annual streamflow and forces the basin toward non-perennial conditions during dry water years. Groundwater declines are amplified in high-relief, conifer-dominated catchments. Upscaling model results across the region indicates concentrated risk of groundwater decline in the Colorado Headwater and Gunnison Basins. Research highlights the tight coupling of topography, vegetation and groundwater dynamics and that excluding groundwater response to warming will underestimate future reductions in mountain streamflow.

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