Snow Cover Monitoring with MODIS Satellite Data in the Arctic Inventory and Monitoring Network, Alaska, 2000-2013

Swanson, David

Snow cover was monitored in the five National Park Service (NPS) units of the Arctic Inventory and Monitoring Network (ARCN) from the fall of 2000 through the spring of 2013, using 500 m resolution daily data from the MODIS Terra satellite. The MODIS data were processed by the National Snow and Ice Data Center (NSIDC) and the Geographic Information Network for Alaska (GINA) at the University of Alaska Fairbanks to detect the first and last snow days of each season, and the start and end of the continuous snow season (CSS). The median first snow day was in October over most of the low-elevation areas (<2000 feet, 620 m) of ARCN and mainly in September at higher elevations, except at elevations above 3000 feet (914 m) along the north side of the Brooks Range, where the first snow came in August. The start of the CSS was within 2 weeks of the first snow day over most of ARCN: late October in the lowlands (<1000 feet, 305 m) of western ARCN and early October elsewhere, except at elevations above 3000 feet (914 m), where the CSS began in September. In years with late snow cover establishment and cloudy fall weather, the date of first snow and the start of the CSS were not detected in some parts of ARCN before winter darkness and long terrain shadows obscured the ground. While this problem appears to not have substantially affected the long-term median values for first snow day and start of CSS, it prevented analysis of year-to-year variability in these two metrics. The median length of the continuous snow season was 6 to 7 months in most lowland areas (below 1000 feet, 305 m), 7 to 8 months at most mid-elevations, and 8 to 9 months at most high elevations (above 4000 feet, 1219 m). The median last snow day and median last day of the CSS were less than a week apart in May over most of ARCN. Higher elevations in ARCN generally had later snow-off dates, though there was some interesting variability within this overall pattern. Snow usually disappeared in April and early May in valleys on the north side of the Brooks Range in Gates of the Arctic National Park and Preserve, in parts of the Noatak Valley, and on the hills that face the Chukchi Sea in Cape Krusenstern National Monument. These anomalous early snow-off areas probably had thin snow covers as a result of both high winds and relatively low snow precipitation. Over most of ARCN the standard deviation in end of CSS was 14 days or less, which means that the snow disappeared within the same 1-month period in about 2 out of 3 years. Variability was greatest on slopes along the northern edge of the Brooks Range. The years with the most extreme deviation in end of CSS were 2001 (late snow persistence) and 2004 (early snow cover loss). Linear regression of end of CSS vs. year and last snow day vs. year for individual pixels showed no significant trend over the period 2001-2013 in our study area.

Snow Cover Monitoring with MODIS Satellite Data in the Arctic Inventory and Monitoring Network, Alaska, 2000-2013

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