The eect of glacier wastage on the ¯ow of the Bow River at Ban, Alberta, 1951±1993 Chris Hopkinson* and Gordon J. Young Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, Ontario, N2L 3C5, Canada. Abstract: A surface area/volume relationship was used to estimate total glacier volumes for the highly glacierized Hector Lake Basin (281 km 2 ) in the Canadian Rockies in the years 1951 and 1993. The change in volume was calculated and this value then extrapolated up to the Bow Basin at Ban (2230 km 2 ) based on relative proportions of glacier cover. The mean net glacier volume loss estimate of 934  10 6 m 3 was divided into annual proportions of glacier wastage and storage using a local mass balance record collected at Peyto Glacier in the Mistaya Valley, contiguous to the Bow Basin. Unfortunately, the record began in 1966 and a hind-cast to 1952 (hydrological year) was necessary. Ban maximum summer temperature and Lake Louise snow course data were used as surrogates for summer and winter glacier mass balance, respectively. Monthly wastage proportions were estimated for 1967±1974 by using modelled values of glacial melt as a template. Glacier wastage inputsto and storage held back from the Bow River hydrograph at Ban were compared with known basin yields to assess the hydrological eects of glacier volume change. For 1952±1993, the average annual wastage/basin yield ratio was found to be around 1 . 8%. For the extremely low ¯ow year of 1970 this ratio increased to 13%. The proportion of ¯ow derived from glacier wastage in August of thisyear was estimated to be around 56%. Although the results tend to con®rm the regulatory eect of glaciers on stream ¯ow, it was found that in someyears of low ¯ow this situation has been aggravated by water being held in glacial storage. # 1998 John Wiley & Sons, Ltd. KEY WORDS glacier wastage; Bow River; volume change; water resources; basin yield; climate change INTRODUCTION Since the middle of the nineteenth century, an irregular but general rise in global temperatures has been recorded (IPCC, 1995) and many mountain glaciers have responded by retreating to higher elevations. The consequences of glacier wastage (see Glossary) are an increase of stream ¯ow above the net income of annual precipitation and rises in global sea level (Meier, 1984). It is to be expected that in warmer and drier years, especially if coupled with low winter snow accumulation, the more glaciers will retreat (net negative mass balance) and the more signi®cant will be their role in stream ¯ow augmentation and sea level rise (Dyurgerov and Meier, 1997). Conversely, in years of high snow fall and/or little melt, glaciers may `grow' (net positive mass balance) and hold back water from the downstream hydrological system. For these reasons glaciers are generally considered to be ecient stream ¯ow regulators (e.g. Meier, 1969, 1973; Fountain and Tangborn, 1985). CCC 0885±6087/98/111745±18$1750 Received 23 May 1997 # 1998 John Wiley & Sons, Ltd. Revised 29 December 1997 Accepted 27 March 1998 Hydrological Processes Hydrol. Process. 12, 1745±1762 (1998) *Correspondence to: C. Hopkinson, Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada. Contract grant sponsor: Alberta Environmental Protection; CRYSYS.