Towards predicting streamflow based on SWE, melt timing, and topography in subarctic heterogeneous terrain

Snowmelt onset date and snow water equivalent (SWE) are major factors that influence the spring runoff in high latitude, snow dominated basins. We combine AMSR-E L3 daily SWE from March to June 2003-2006, daily hydrological records from 3 sites on the Pelly and Ross Rivers, Yukon Territory [Pelly Crossing N62.82¡ã, W136.58¡ã, Faro N62.22¡ã,W133.37¡ã, and Ross River N61.99¡ã,W132.37¡ã], and a 1:250,000 DEM to develop a technique to predict streamflow in subarctic heterogeneous terrain. The AMSR-E L3 SWE algorithm was developed for global snow cover distributions; it is not optimized for heterogeneous terrain. Field data suggest that it underestimates the SWE in this area. We assume it represents the minimum SWE per pixel. SWE variations of the Pelly River basin (49,000 km2) and its two nested sub-basins (22,100 km2 and 7,250 km2), show that SWE had an apparent drop shortly after the snowmelt onset date determined from Tb and diurnal amplitude variations (DAV), which are also correlated with temperature change. During the early stage of snowmelt, high and low elevations have no significant SWE difference. After mid-April, the most intense melt period at lower elevations, low elevation SWE drops far below high elevation SWE, which is just beginning the melt process. Initial melt and the drop in low elevation SWE likely cause the first small discharge peak in the hydrograph. When the SWE throughout the basin approaches 0 mm for more than 3 days, it is followed by the peak flow. The largest basin has an about 14 day lag between the SWE drop and the flow increase, while the smaller basins have an about 9 day lag. Snow distribution, melt, runoff, and the lag times vary due to diverse terrain and microclimate factors such as: forest cover, permafrost, temperature and precipitation. By combining topography, snow distribution and melt timing, we have developed an understanding of basin-specific stream discharge response to spring thaw. Passive microwave derived daily SWE data combined with terrain and melt timing have significant potential for constraining and predicting stream flow timing and magnitude during the melt season in subarctic regions.