Decadal Changes In Climate And Hydrological Responses In High Elevation Catchments, Colorado Front Range
Williams, Mark W 1 ; Hill, Ken 2 ; Caine, Nel 3
1 CU-Boulder
2 National Park Service
3 CU-Boulder
Potential climate impacts on the hydrochemistry of two seasonally snow covered catchments is evaluated using 24 years of data from Niwot Ridge Long Term Ecological Research Site, Colorado. At the larger (220 ha), higher elevation (3570 m) GL4 catchment annual discharge did not change significantly based on nonparametric trend testing. However, October streamflow volumes and groundwater storage did increase, despite drought conditions near the end of the record in 2000-2004. In contrast, at the smaller (8 ha), lower elevation (3400 m) MART catchment, annual discharge decreased significantly over the study period with the most substantial changes in July-September. The study period was separated into "wet", "normal", and "dry" years based on the 75th and 25th quartiles of annual precipitation. Results indicate that MART is particularly sensitive to changes in precipitation with dry years exhibiting decreased snowmelt peak flows, earlier snowmelt timing, decreased annual discharge, and reduced late-season flows. GL4 was less susceptible to changes in precipitation and surprisingly late-season flow volumes (Sept.-Oct.) were not significantly different between wet, normal, and dry conditions. Surprisingly, during dry years both the concentrations and annual fluxes of Ca2+ and SO42- increased in the outflow of GL4, but not at the Martinelli catchment. These differeneces in hydrochemistry were particularly pronounced during the low-flow period. Streamwater chemistry in GL4 during drought years resembled that of permafrost, suggesting augmented flow during the fall due to permafrost melt. This study shows that seasonally snow covered catchments are particularly sensitive to changes in climate, but the hydrochemical response may depend on landscape characteristics.