Impact of an extreme melt event on the runoff and hydrology of a high Arctic glacier

On 28-30 July 2000, an extreme melt event was observed at John Evans Glacier (JEG), Ellesmere Island (79degrees40'N, 74degrees00'W). Hourly melt rates during this event fell in the upper 4% of the distribution of melt rates observed at the site during the period 1996-2000. Synoptic conditions during the event resulted in strong east-to-west flow over the northern sector of the Greenland Ice Sheet, with descending flow on the northwest side reaching Ellesmere Island. On JEG, wind speeds during the event averaged 8(.)1 m s(-1) at 1183 m a.s.l., with hourly mean wind speeds peaking at 11(.)6 m s(-1). Air temperatures reached 8degreesC, and rates of surface lowering measured by an ultrasonic depth gauge averaged 56 mm day(-1). Calculations with an energy balance model suggest that increased turbulent fluxes contributed to melt enhancement at all elevations on the glacier, while snow albedo feedback resulted in increased melting due to net radiation at higher elevations. The event was responsible for 30% of total summer melt at 1183 m a.s.l. and 15% at 850 m a.s.l. Conditions similar to those during the event occurred on only 0(.)1% of days in the period 1948-2000, but 61% of events occurred in the summer months and there was an apparent clustering of events in the 1950s and 1980s. Such events have the potential to impact significantly on runoff, mass balance and drainage system development at high Arctic glaciers, and changes in their incidence could play a role in determining how high Arctic glaciers respond to climate change and variability. Copyright (C) 2003 John Wiley Sons, Ltd.