This paper advances an objective method of diurnal hydrograph classi®cation as an aid to exploring changes in the hydrological functioning of glacierized catchments over the ablation season. The temporal sequencing of dierent hydrograph classes allows identi®cation of seasonal evolution in hydrograph form and also assists delimitation of hydrologically-meaningful time periods of similar diurnal discharge response. The eectiveness of this approach is illustrated by applying it to two contrasting summer discharge records for a small cirque basin. By comparing the results with patterns of surface energy receipt and glacier ablation, the seasonally transient relative in¯uences of: (i) surface meltwater production and (ii) meltwater routing and storage conditions within the intervening glacier drainage system in determining runo are elucidated. The method successfully characterizes distinct seasonal-scale changes in the diurnal out¯ow hydrograph during the ablation-dominated 1995 melt season but is also able to reveal underlying trends and short-term ¯uctuations in the precipitation-dominated, poorly ablation-regulated 1996 melt season. The limitations and bene®ts of this hydrograph classi®cation technique are evaluated.