The Hydrogeology of Cold Regions in a Warming World

• Main Author: Evans, Sarah Grace
• Format: Text
• Language: unknown
• Published: CU Scholar 2017
• Subjects: groundwater; hydrogeology; numerical modeling; permafrost; seasonally frozen ground; snowmelt; Environmental Sciences; Geology; Hydrology
• Online Access: https://scholar.colorado.edu/geol_gradetds/118; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1122&context=geol_gradetds

Frozen ground is found extensively at high latitudes and intermittently at high elevation areas at lower latitudes, underlying half of the exposed land surface in the Northern Hemisphere. In these cold regions, frozen ground acts as an aquitard, impeding downward groundwater flow while simultaneously enhancing groundwater-surface water interactions. Frozen ground falls into two major categories: seasonally frozen ground, where the minimum annual ground surface temperature is less than 0°C and the shallow subsurface freezes and thaws annually, and perennially frozen ground or permafrost, where the subsurface temperature is at or below 0°C for two or more consecutive years. As global air temperatures increase, frozen ground degrades. Frozen ground degradation alters groundwater recharge, groundwater contribution to stream flow, and consequently, vital freshwater supplies to lowland regions. This dissertation evaluates the effects of warming on groundwater discharge in representative cold regions. Coupled heat transfer and groundwater flow processes are modeled for a suite of catchments, including sites on the Qinghai-Tibet Plateau, China and in the Colorado Rocky Mountains, USA. Results for a suite of representative cold region hillslopes demonstrate that after a century of warming, groundwater discharge increases for both kinds of frozen ground, but permafrost experiences a larger increase than seasonally frozen ground hillslopes. In a continuous permafrost catchment on the Qinghai-Tibet Plateau, China, 2°C of warming causes groundwater discharge to streams to increase three-fold. However, increases in groundwater discharge are only sustainable if there is adequate recharge upstream to replenish increased discharge downstream. To analyze how changes in recharge may alter groundwater discharge, a site-specific study was conducted in a seasonally frozen ground catchment in the Rocky Mountains of Colorado, USA. Five plausible snowmelt recharge scenarios were examined. After 50 years with a warming trend of 4.8°C/100 years, annual groundwater discharge increased an average of 1% with an increase of 7% in the spring (March-May) and decrease of 9% in the summer (June-August). These findings help provide a basis for anticipating future water resource changes in cold regions. Anticipated changes in the seasonality and magnitude of groundwater discharge will likely impact aquatic ecosystems and downstream human communities.