Date of Award

5-2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences

First Advisor

Crystal B. Schaaf

Second Advisor

Jarrett Byrnes

Third Advisor

Karen Ricciardi

Abstract

The climate is warming two to three times faster in the Arctic than in other places on the globe. Associated with this change are multiple biophysical feedback relationships with the potential to contribute both positively and negatively to the overall warming and cooling of these regions. As a key factor in these relationships, land albedo plays an important role in the surface energy budget as it represents the proportion of incoming solar radiation reflected directly back to space, and consequently, that which is available to drive photosynthesis and surface heating. To examine albedo dynamics across arctic systems, dynamic, cloud-free, near-nadir imagery from the Landsat-8 Operational Land Imager (OLI) provides excellent information on the surface heterogeneity and vegetation status over land and, when combined with multi-angle reflectance information, such as from the MODerate-resolution Imaging Spectroradiometer (MODIS), can capture the full effects of surface reflectance anisotropy to produce realistic bihemispherical albedo quantities. These improved spatial resolution estimates of the land surface albedo, particularly in response to seasonal variation, snow cover, and ecosystem disturbance, can identify and quantify contributions from smaller scale landscape characteristics on system-wide albedo trends. As presented here, an evaluation of the Landsat-8 albedo product with ground measured tower data from twenty-six locations across the northern circumpolar domain indicate minimal product bias and a root mean square error of 0.0426. Specifically, the studies here use higher resolution Landsat albedo to examine the influence of gradual and abrupt shifts in northern high latitude ecosystems. Looking across the circumpolar vegetated domain in North America, the impact of increasing and decreasing vegetation indices (greening and browning) on seasonal albedo trajectories is investigated. Additionally, the albedo impact of changes in surface water coverage and the size distribution of surface water systems are examined across the entire circumpolar vegetated domain and in more depth on a subset of the Canadian tundra. Lastly, the impact of boreal fires on the surface shortwave forcing are examined and drivers such as pre-fire land cover and burn severity are investigated.

Comments

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