Evans, Sarah听1听;听Ge, Shemin听2
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2听精品SM在线影片
In mountainous regions, warmer air temperatures have led to an earlier onset of spring snowmelt and lower snowmelt rates because snow melts at a slower rate earlier in the year when the net turbulent energy flux is lower. These changes to snowmelt will likely affect the partitioning of snowmelt water between surface runoff and groundwater flow, and therefore, the lag time between snowmelt and streamflow since melt water will travel more slowly to streams as groundwater flow than surface runoff. While the connection between snowmelt and surface runoff has been well-studied, the impact of snowmelt variability on groundwater flow processes has received limited attention, especially in mountainous headwater catchments.
We construct a two-dimensional, finite element, coupled flow and heat transport hydrogeologic model to evaluate how changes in snowmelt rate may alter groundwater discharge to streams in mountainous catchments. The coupled hydrogeologic model simulates seasonally frozen ground by incorporating permeability variation as a function of temperature and allows for modeling of pore water freeze and thaw. We apply the model to the Green Lakes Valley (GLV) watershed in the Rocky Mountains of Colorado. Snowmelt for the GLV catchment is reconstructed from a 12 year (1996-2007) dataset of hydrometeorological records and satellite-derived snow covered area.
Results suggest that under average conditions from 1996 to 2007, maximum groundwater discharge to the surface lags maximum snowmelt by approximately two months. Under a 30 year long warming scenario where mean annual surface temperature is increased by 1听oC/decade and the onset of snowmelt is 4 days earlier in the year/decade, groundwater discharge to streams reaches a maximum approximately 20 days earlier in the year than in the present-day scenario. While total baseflow remains constant between the two scenarios, average rate of groundwater discharge to streams decreases by 7%. These findings indicate that there may be declines in groundwater contribution to summer streamflow. Reductions in summer streamflow has the potential to exacerbate freshwater deficits to downstream, lowland regions.