Investigating the Hydrogeologic Controls on Memory and Feedbacks to Climate Change in Mountain Groundwater Systems: An Integrated Modeling Approach

Abstract:

Rising global temperatures are profoundly impacting alpine environments by shifting the precipitation type and the timing of peak snowmelt runoff. Uncertainty in the magnitude of these shifts translates to uncertainty in how climate change affects timing of snowmelt runoff, and hence availability of surface water during the remainder of the year. Integrated hydrologic models are useful tools for capturing these feedbacks by closing the loop between atmosphere, land surface, and subsurface dynamics. Recent integrated models have been used to predict streamflow response to climate change in mountain basins, however these models assume that shallow, local flow paths comprise the majority of recharge and baseflow to streams. Several studies have challenged this assumption with discordant groundwater ages and hysteresis loops, suggesting that deep, regional flow paths may play a more substantial role even at the local stream scale. This would have considerable implications for predicted responses to climate change in alpine basins, as deep, regional groundwater would initially buffer perturbations, but exhibit greater memory over the long-term. The goal of this study is to understand how various hydrogeological settings will control the relative feedbacks to climate change.

This research uses three simplified, conceptual hillslope models: a “fast” draining, low storage, granodiorite similar to that of of the Sierra Nevada or Himalayan mountain range, a “slow” draining, high storage basalt of the Cascade or Andes Range, and a vertically homogeneous “base” case. The relative response of these hillslopes to three future climate scenarios: warm, warm and dry, and warm and wet are tested using ParFlow, an integrated surface water-groundwater model, coupled with CLM, a land surface model. These models will help quantify the relative feedbacks of deep groundwater in various hydrogeologic settings and will ultimately be scaled up to assess the 3-D, transient response of deep groundwater to climate change in a regional alpine system.