Hydrological Trends in a High Alpine Watershed in Rocky Mountain National Park

Abstract:

Recent studies reveal amplified air temperature warming trends in the Rocky Mountains than global averages, as well as earlier snowmelt timing and decreased snow-water equivalent (SWE) relative to past records in this region. Changes in SWE and snowmelt runoff timing directly impact water availability in alpine watersheds as well as downstream ecosystem services. In this study we evaluated local trends in air temperature, precipitation, snowpack, and streamflow timing to look for similarities to regional trends reported in literature. We assessed two long-term alpine data collection sites in Rocky Mountain National Park: Bear Lake SNOTEL site (2896 m; 1981–2013) and Loch Vale Watershed (3159 m; 1984–2011), using the Mann-Kendall test to examine trends in average monthly temperature, number of days above freezing, peak SWE depth and timing, number of snow-free days, and total precipitation at Bear Lake, as well as streamflow volume and timing metrics at the outlet of Loch Vale.

We found seasonal patterns and magnitudes of warming similar to regional trend findings, with significant increasing trends in average monthly mean air temperatures for most months. The average number of days below 0ºC also significantly decreased in fall and winter. However, we found no significant trends in peak SWE, discharge rate, precipitation, accumulated snowfall, or the number of snow-free days at Bear Lake or Loch Vale sites. These results suggest reported regional warming trends are not reflected in localized snowmelt trends in alpine Rocky Mountain watersheds.