Abstract
Abstract. Warm and dry summer days can lead to low streamflow due to a lack of rainfall and increased evaporation. In glacierized catchments, however, such periods can lead to a very different hydrological response as glaciers can supply an increased amount of meltwater, thereby compensating for the rainfall deficits. Here, we analyzed glacier-fed streamflow responses to warm and dry (WD) periods in long-term streamflow observations (>50 years). WD events during summer (June–September) were analyzed for catchments with varying glacier cover in western Canada, southwestern Norway, and the European Alps. WD events were defined by days with temperatures above a daily varying threshold, based on the 80th percentile of the respective long-term temperature data for that day in the year, and daily precipitation sums below a fixed threshold (<2 mm d−1) for a minimum duration of 7 d. Streamflow responses to these WD events were expressed as level of compensation (C) and were calculated as the event streamflow relative to the long-term streamflow regime. C≥100 % indicates that increased melt and other catchment storages could compensate, or even overcompensate, the rainfall deficit and increased evaporation. Results showed a wide range of compensation levels, both between catchments and between different WD events in a particular catchment. C was, in general, higher than 100 % for catchments with a relative glacier cover higher than 5 %–15 %, depending on region and month. June was the month with highest compensation levels, but this was likely more influenced by snowmelt than by glacier melt. For WD events in September, C was still higher than 100 % in many catchments, which likely indicates the importance of glacier melt as a streamflow contributor in late summer. There was a considerable range in C of different WD events for groups of catchments with similar glacier cover. This could be partly explained by antecedent conditions, such as the amount of snow fallen in the previous winter and the streamflow conditions 30 d before the WD event. Some decreasing trends in C were evident, especially for catchments in western Canada and the European Alps. Overall, our results suggest that glaciers do not compensate straightforwardly, and the range in compensation levels is large. The different streamflow components – glacier, snow and rain – and their variations are important for the buffering capacity and the compensating effect of glaciers in these high mountain water systems.
Highlights
Dry periods and heat waves negatively affect water availability (e.g., Stahl et al, 2016; Teuling, 2018; van Loon, 2015; Zappa and Kan, 2007)
While most previous studies have looked at (a) relatively dry year(s) or summer(s) to analyze the glacier buffer effect, we focus here on the hydrological response to specific warm and dry events, i.e., short periods that are characterized by days with no to very low rain amounts and days with relatively high temperatures
Catchments in the European Alps had most of the events in July and September, while in southwestern Norway and western Canada there were more events in June and July
Summary
Dry periods and heat waves negatively affect water availability (e.g., Stahl et al, 2016; Teuling, 2018; van Loon, 2015; Zappa and Kan, 2007). This means that during such combined dry and warm periods, streamflow decreases, and soil and groundwater storages are depleted. M. Van Tiel et al.: Glacierized catchment response to warm and dry events agricultural production, problems with water supply, and forest fires (COGECA, 2003; Jonkeren et al, 2007; Rouault et al, 2006; Stahl et al, 2016). In some glacierized catchments in, for example, Switzerland and Austria, streamflow was above the long-term average during this extreme summer (Koboltschnig et al, 2009; Koboltschnig and Schöner, 2011; Zappa and Kan, 2007). Snow and ice storages provide an additional source of water, especially during warm and dry periods, because of temperature-driven instead of only precipitation-driven water supply
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