Near record precipitation causes rapid drainage of Zelma Lake, Old Crow Flats, Northern Yukon Territory

Abstract

While conducting the first phase of hydrological fieldwork in June 2007 for the Government of Canada International Polar Year project, “Environmental change and traditional use of the Old Crow Flats in northern Canada,” we observed the rapid overland drainage of Zelma Lake. The Old Crow Flats (OCF), a 5300 km2 freshwater ecosystem in the northern Yukon, is internationally recognized for its ecological significance and is closely linked to the cultural identity of the Vuntut Gwitchin community of Old Crow. Zelma Lake stands out among the more than 2000 lakes in the OCF because of its large size, its accessibility by boat, and because local residents have long used it for hunting, trapping and fishing. We used aerial photographs from a later survey in July 2007 as well as water depth measurements to estimate that water loss of approximately 5.8 million cubic metres (the equivalent of about 2300 Olympic-size swimming pools) exposed about 5.2 square kilometres of lake bed, corresponding to 43% reduction in lake area and over 80% reduction in lake volume. Precipitation in the month of May prior to our fieldwork totalled 44.4 mm, the highest recorded since measurements began in 1951; this followed above-average cumulative precipitation during the previous two months. Analysis of lake water isotope composition from Zelma Lake indicates that substantial rainfall likely increased lake levels and ultimately triggered rapid erosion of an outlet leading to the channel network that exports water from the Flats.