Elevation dependent landscape processes in rapidly warming sub-Arctic mountains: influences of snow, temperature and vegetation

• Author / Creator

  Williamson, Scott N

• The loss of spring snow in the Northern Hemisphere has been dramatic. From 1967 to 2008 snow cover decreased by 14% in May and 46% in June, with a simultaneous reduction in snow cover duration of 6 – 8 days per decade in both summer and fall. These effects have been particularly pronounced in the Kluane region of the southwest Yukon, making the area well suited for a detailed study of the effects of the reciprocal interactions of snow cover decline with ecological, geographical and climatological features. The mountainous Kluane region, like most of the Arctic, is difficult to access and has few long-term ground-based observations, which necessitates the use of remote sensing and mathematical modelling to determine surface characteristics.
  
  This thesis integrates data from diverse sources including meteorological stations, field albedo measurements, downscaled surface temperature, infrared Land Surface Temperature (LST), snow cover, land cover, and cloud cover to quantify the snow albedo feedback in the southwest Yukon.
  
  The first four chapters of this thesis addresses the validation and integration of different sources of data. My main findings are that (i) cloud contamination of MODIS-derived day-time LST within the study area is ~15%, which cools affected grid cells by no more than 2 K; (ii) combining night-time with day-time LST leads to a cold bias when compared to temporally averaged (8-day or monthly) air temperature; and (iii) the cold bias gets larger as within grid cell snow fraction increases.
  
  The last three chapters of my thesis attempts to account for various feedback processes using a combination of field measurements and modeling studies. Following spring snow melt, albedo increases for woody tundra vegetation as the growing season progresses, but the increase is small in magnitude compared to the albedo difference between snow covered and snow-free land. The albedo increase caused by the progressive canopy closure of woody vegetation is differentiated by stature and species, a result that will influence tundra energy balance on a successional timescale in a wetter, warmer Arctic. Finally, I demonstrate that the 35 – 50% decrease in snow cover in tundra in May between 2000 and 2008 produces a small radiative feedback to climate, but the strength is insufficient to influence the monthly average temperature change. This suggests that snow cover and temperature change is largely the result of external forcing consistent with meridional heat transport. Furthermore, the similarity in temperature trends among three land cover types (Icefields, Conifer forests with no snow, and Tundra characterized by a large decrease in snow cover) indicates that the snow cover albedo feedback contributes < 6% (or the equivalent of <0.091 W m-2 per decade over the 2000 to 2008 study period) to the changes observed in air temperature. Consequently, if the atmospheric local heating related to the large albedo decrease caused by snow cover decline is small, the much smaller albedo changes caused by successional changes in vegetation will be negligible over the short-term.

• Subjects / Keywords

  • Snow albedo feedback
  • Climate
  • Land Surface Temperature (LST)

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3222RH36

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.