Groundwater Dynamics in Headwater Regions under a Changing Climate

Groundwater systems receive significant recharge in high-altitude headwater regions. Seasonal and long-term 
variations in surface temperature and precipitation are expected under a changing climate, which could 
substantially impact groundwater recharge and subsequently groundwater storage and discharge to surface 
waters. Headwater regions are hydrologically sensitive to surface temperature changes due to the presence of 
frozen grounds that freeze and thaw seasonally and degrading permafrost. The freeze and thaw processes lead 
to changes in subsurface hydrologic properties and dynamically impede or invigorate groundwater flow. A key 
question is how seasonal and long-term surface temperature variations impact recharge to groundwater and its 
interaction with surface water. This presentation addresses this question as it relates to groundwater flow 
in headwater regions. Coupled heat transfer and groundwater flow processes are modeled for two headwater 
catchments, one in the Colorado Rocky Mountains and the other on the Tibet Plateau. These studies illustrate 
that shallow groundwater flow in summer and early fall is most energetic as thawed ground promotes snowmelt 
infiltration, invigorating the exchange between groundwater and surface water. Under increasing temperature 
scenarios, groundwater discharge to surface may experience a several-fold increase in magnitude over the 
decadal scale. While projected warming leads to increased groundwater discharge to surface waters, in the 
long run, insufficient recharge upstream will make it challenge to sustain the discharge.