Quantifying the effects of freeze-thaw transitions and snowpack melt on land surface albedo and energy exchange over Alaska and Western Canada

Abstract

Variations in land surface albedo and snow-cover strongly impact the global biosphere, particularly through the snow-albedo feedback on climate. The seasonal freeze-thaw (FT) transition is coupled with snowpack melt dynamics and strongly impacts surface water mobility and the energy budget in the northern (≥45 • N) arctic and boreal region (ABR). However, understanding of the regional variation in snowmelt and its effect on the surface energy budget are limited due to sparse in situ measurements of these processes and environmental constraints on effective monitoring within the ABR. In this study, we combined synergistic observations from overlapping satellite optical-infrared and microwave sensor records to quantify the regional patterns and seasonal progression in wet snow conditions during the spring snowmelt and autumn snow accumulation periods across Alaska and western Canada. The integrated satellite record included daily landscape FT status from AMSR microwave brightness temperature retrievals; and snow-cover extent, black sky albedo and net shortwave solar radiation (R snet ) derived from MODIS and AVHRR observations. The integrated satellite records were analyzed with in situ surface air temperature and humidity observations from regional weather stations over a two-year study period (2015-2016) overlapping with the NASA ABoVE (Arctic Boreal Vulnerability Experiment). Our results show a large (79%) mean decline in land surface albedo between dry snow and snow-free conditions during the spring (March-June) and autumn (August-November) transition periods. Onset of diurnal thawing and refreezing of the surface snow layer and associated wet snow conditions in spring contributed to an approximate 25% decrease in snow cover albedo that extended over a seven to 21 week snowpack depletion period. The lower wet snow albedo enhances R snet by approximately 74% (9-10 MJ m −2 d −1 ) relative to dry snow conditions, reinforcing snowmelt and surface warming, and contributing to growing season onset and activation of biological and hydrological processes in the ABR. These results contribute to better understanding of snow albedo feedbacks to Arctic amplification, and the representation of these processes in global Earth system models.

Global Assessment of the SMAP Freeze/Thaw Data Record and Regional Applications for Detecting Spring Onset and Frost Events

“…The growing season onset indicated by the SMAP L4_C GPP record lagged the primary thaw timing by approximately 46 ± 24 (spatial SD) days over Alaska (Figure 7). The SMAP FT record indicates generally earlier spring thaw timing than the FT retrievals from higher frequency (~37 GHz) Tb measurements [4,65]. These results, which are consistent with earlier studies, indicate that the SMAP L-band FT record may be more sensitive to initial surface thawing and wet snow conditions within a deeper snow layer, relative to higher frequency retrievals that are sensitive to more ephemeral surface FT variations [9,24,66].…”

Framework to Study the Effects of Climate Change on Vulnerability of Ecosystems and Societies: Case Study of Nitrates in Drinking Water in Southern Finland

“…We used here albedo data to improve simulation of the timing of the snow-covered period. For example, [52] showed a large mean decline in land surface albedo between dry snow and snow-free conditions, so that the lower wet snow albedo contributed to growing season onset and activation of biological and hydrological processes.…”

Remote Sensing of Environmental Changes in Cold Regions: Methods, Achievements and Challenges

“…The landscape FT status is closely linked to ecosystem carbon, water and energy exchanges, snow melt dynamics, and permafrost extent and stability [21,34,[149][150]. Global FT observational data records spanning the modern satellite era have been used to document environmental trends from global warming, including earlier and longer non-frozen seasons as a driver of northern vegetation greening, increased trends in damaging frost events in early spring [9], degrading permafrost, and an earlier spring flood pulse across the pan-Arctic [151].…”

“…The timing and duration of the non-frozen season is an important factor affecting water, carbon, and energy budgets in cold land areas. Recent trends toward earlier and longer non-frozen seasons coincide with global warming and have been shown to be a major driver of northern vegetation greening, active layer deepening and permafrost degradation, enhanced evapotranspiration, earlier snowmelt onset, and associated changes in terrestrial water and energy budgets [21,34,149]. For example, satellite observations indicate that the snow end date in spring advanced by 5.11 days from 2001 to 2014 in the high northern latitudes (52-75 • N) [238], along with shorter lake ice cover duration at higher latitudes from 2002 to 2015 [17].…”