| Description |
Glaciers contribute to the hydrology of many mountainous watersheds worldwide. Significant attention has been given to seasonal discharge measurements and modeling and relatively little to shorter timescale glacier discharge; thus, our understanding of high frequency variability is more limited. This high frequency variability impacts sediment flux, hydropower generation, montane ecosystems, and so forth. Here we seek to improve our understanding of glacial meltwater processes that control diurnal melt cycles. In particular, we used isotopic and electrical conductivity measurements and discharge estimates in three glaciated watersheds (Rhonegletscher, Gornergletscher, and Langgletscher) and two nonglaciated watersheds within the Upper Rhone Watershed, Switzerland, to test our understanding of diurnal fluctuations and to validate a glacier melt model. We chose these particular watersheds because they represent a significant range in size, shape, slope, and other topographical features that likely impact the shape, magnitude, timing, and duration of daily peak glacial melt. Physical data show differences in magnitude and timing of peak melt between these watersheds. We use a modeling approach to assess the underlying causes of these differences. In particular, we use a temperature index model to calculate hourly melt on each glacier and model meltwater flow on the glacier’s surface. The modeled melt volumes were used as input for a watershed model that routed all meltwater to the glacier terminus and the proglacial stream system as surface flow. The total volume of meltwater reaching the proglacial stream was tracked, and a modeled hydrograph was produced for each glacierized watershed. We used the resulting hydrograph to evaluate which processes are the dominant controlling factors of diurnal melt, focusing on snowpack and exposed ice, to increase our understanding of high frequency melt variability. Results suggested that by the end of the melt season, the shape of the hydrograph was dominantly controlled by air temperature, and ice melt was the primary contributor to total melt volume. The timing of peak melt is strongly influenced by snowpack distribution; when less than 50% of the glacier surface was snow-covered, we observed no delay in the timing of meltwater delivery to the glacier terminus and the proglacial stream system, while the reverse is true as snow cover exceeds 50%. By identifying these parameters at a high temporal resolution, we create a framework to better understand the impact diurnal variations have on various hydrologic, ecologic, and human systems that rely on glacial melt. |
