Critical elevation zones of snowmelt during peak discharges in a mountain river basin

SummaryIn mountain ranges, elevation correlates with snowmelt through its association with temperature, snow cover, hypsometry and vegetation. A critical elevation zone, where temperatures, snow cover, and the fraction of basin area are high is hypothesized to dominate melt volumes during peak discharge events. The distribution of snowmelt by elevation zone was documented during five peak discharge events in the Merced River Basin, California, using daily MODIS snow covered area (SCA) and a temperature-based melt model. The model successfully reproduced the spatial pattern in runoff measured at two stream gauges. SCA changed rapidly during several events, so daily SCA was essential for accurate estimation of melt, even for periods as short as 6 days. For all events, between 60% and 80% of melt volume occurred in an elevation zone that covered between 22% and 38% of total basin relief. The elevation of the critical zone increased through the melt season, and the center of mass of melt increased from 2425 m in March events to 3093 m in May events. For several events in March and April, the critical zone coincided with a large, flat upland area that covers a significant fraction of the watershed area. Early in the season, the critical zone occurred at a higher elevation than the intermittent area of rapidly changing snow cover, while later in the season the critical zone coincided with an area of rapidly changing snow cover. Forest cover impacted the total volume of melt, but had small effects on the relative distribution of melt among the zones. The critical-zone concept could be used to interpret and predict regional patterns in snowmelt flood peaks based on catchment hypsometry and climate.

► Peak discharges produced by snowmelt are important for water management and geomorphology. ► Daily satellite imagery combined with a snowmelt model documented melt during peaks in the Merced River. ► A critical zone accounted for most melt during peak events. The elevation of the zone increased through the melt season. ► Daily satellite imagery were necessary to predict melt volumes accurately.