Longer spring snowmelt: spatial and temporal variations of snowmelt trends detected by passive microwave from 1988 to 2010 in the Yukon River Basin

Abstract. Brightness temperature (T_b) data from the Special Sensor Microwave Imager (SSM/I) 37 V-GHz frequency provides a time series from 1988 to 2010 that enables the assessment of snowmelt timing trends (onset, end of melt-refreeze, and duration) for the Yukon River Basin. T_b and diurnal amplitude variation (DAV) thresholds determine dates of melt onset and melt-freeze end (end of high DAV), defined as the first date when thresholds are met for more than three of five consecutive days. Temporal and spatial trends in melt onset and end of melt-refreeze date are determined with varying time period intervals and for each sub-basin and elevation class. Earlier melt onset trends are found in the highest elevations and northernmost sub-basins (Porcupine, Chandalar, and Koyukuk Rivers). Significant later (>0.75 d yr⁻¹) end of melt-refreeze and longer melt duration trends are found in a majority of the sub-basins. Moving interval trends suggest interannual variability within the time series and a power spectrum analysis reveals peak frequencies and periods of 5–7 and ~11 years, possibly related to El Nino- Southern Oscillation and the solar cycle, respectively. Latitude and elevation display the dominant controls on timing variance and spring solar flux is highly correlated with melt timing in middle elevations.