Chinooks and winter evaporation

Abstract

Chinooks are warm mountain winds which occur in the foothills of southern Alberta. They are often blamed for encouraging droughts in the western prairies because of the link believed to exist between them and excessive surface and subsurface evaporation. Measurements made over four winters show that evaporation rates during a chinook exceed the net radiation flux when there is water standing over the surface. However, the vapour flux fraction reduces to a level below the potential rate once the moisture content drops below saturation level within the upper subsurface layer no thicker than 2 mm. Meanwhile, the soil moisture reservoir below that layer remains virtually undepleted even in the face of persistently strong chinook events.