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K. Semmens, J. Ramage, A. Bartsch, G. Liston:
"Early snowmelt events: detection, distribution, and significance in a major sub-arctic watershed";
Environmental Research Letters, 8 (2013), 11 pages.

High latitude drainage basins are experiencing higher average temperatures, earlier snowmelt onset in
spring, and an increase in rain on snow (ROS) events in winter, trends that climate models project into the
future. Snowmelt-dominated basins are most sensitive to winter temperature increases that influence the
frequency of ROS events and the timing and duration of snowmelt, resulting in changes to spring runoff. Of
specific interest in this study are early melt events that occur in late winter preceding melt onset in the
spring. The study focuses on satellite determination and characterization of these early melt events using the
Yukon River Basin (Canada/USA) as a test domain. The timing of these events was estimated using data
from passive (Advanced Microwave Scanning Radiometer-EOS (AMSR-E)) and active (SeaWinds on
Quick Scatterometer (QuikSCAT)) microwave remote sensors, employing detection algorithms for
brightness temperature (AMSR-E) and radar backscatter (QuikSCAT). The satellite detected events were
validated with ground station meteorological and hydrological data, and the spatial and temporal variability
of the events across the entire river basin was characterized. Possible causative factors for the detected
events, including ROS, fog, and positive air temperatures, were determined by comparing the timing of the
events to parameters from SnowModel and National Centers for Environmental Prediction North American
Regional Reanalysis (NARR) outputs, and weather station data. All melt events coincided with above
freezing temperatures, while a limited number corresponded to ROS (determined from SnowModel and
ground data) and a majority to fog occurrence (determined from NARR). The results underscore the
significant influence that warm air intrusions have on melt in some areas and demonstrate the large temporal
and spatial variability over years and regions. The study provides a method for melt detection and a baseline
from which to assess future change.

nowmelt, passive microwave, active microwave, rain on snow, remote sensing, cryosphere

http://dx.doi.org/10.1088/1748-9326/8/1/014020