Why do glacier-fed tributaries of the Yukon River reach peak flow in July?

Glacier-fed tributaries of the Yukon River, such as the White River, reach their peak flow in July because of the timing of glacial melt.1

While solar radiation—the primary heat source for melting—peaks in June, the maximum runoff from glaciers is delayed until midsummer. This delay occurs primarily due to changes in the glacier's albedo, or surface reflectivity. Early in the summer, the glacier is covered by highly reflective snow, which limits melting. As the summer progresses, this snowpack thins and becomes wetter, eventually exposing the underlying ice, which has a much lower albedo and absorbs significantly more solar energy. Additionally, other heat-exchange processes, such as the transfer of heat from warm air, become more influential during this period, further accelerating the melt and resulting in the greatest runoff occurring in July.21