Potential Shifts In The Seasonality Of Groundwater Discharge As Snowmelt-Dominated Watersheds Warm
Evans, Sarah 1 ; Ge, Shemin 2 ; Molotch, Noah 3
1 Unviersity of Colorado Boulder
2 Unviersity of Colorado Boulder
3 Unviersity of Colorado Boulder
Climate warming is expected to alter groundwater discharge to streams in alpine watersheds due to changes in the timing of snowmelt recharge and the persistence of seasonal freezing in the subsurface. It is imperative to understand the effects of warming on groundwater discharge to streams in alpine watersheds as streamflow from these watersheds is a critical water resource for downstream users. This study evaluates how climate warming will alter groundwater discharge due to changes in snowmelt and seasonally frozen ground using a 2D coupled flow and heat transport model with freeze and thaw capability for variably saturated media. The model is applied to a representative snowmelt-dominated watershed in the Rocky Mountains of central Colorado. Snowmelt time series are reconstructed from a 12-year dataset of hydrometeorological records and satellite-derived snow-covered area with field measurements. Simulations indicate that seasonal freezing and thawing of the subsurface controls groundwater discharge to streams while snowmelt controls groundwater discharge to hillslope faces. Climate warming increases groundwater discharge to streams and decreases groundwater discharge to seepage faces. After 50 years with a warming trend of 4.8°C/100 years and four snowmelt recharge scenarios, annual groundwater discharge decreased an average of 6% with an increase of 5% in the spring (March-May) and decrease of 14% in the summer (June-August). Should these changes continue over longer time periods, they may cause significant local ecological and downstream hydrologic impacts.