Runoff variability from small catchments in West Greenland

Abstract:

The majority of the freshwater input from Greenland stems from the Greenland Ice Sheet. However, despite its importance in terms of freshwater totals, there are almost twice as many basins off the ice sheet with local glacier and ice cover only (Mankoff and others, 2020). Only very few of them are instrumented and little scientific literature exists. We explore a dataset of four catchments in Kobbefjord, West Greenland, close to Greenland’s capital Nuuk that remains hitherto unpublished apart from annual discharge totals (Deuerling and others, 2019) and an analysis of an extreme snow-hydrological event (Abermann and others, 2019). The fjord is particularly well studied since it is home to the interdisciplinary Greenland Ecosystem Monitoring programme (www.g-e-m.dk). We analyze four catchments of different size (between 7 and 32 km²) and local glacier coverage (4-11%) and present 12 years of discharge derived from continuous water level measurements in lakes and rivers and a stage-discharge relation based on more than a dozen of manual measurements for each site. Uncertainties in discharge estimation are discussed as well as the local variability of discharge depending on the physical characteristics of the catchment and the local climate variability. We find that Pardé coefficients vary significantly among the catchments and relate this to variations in glacier coverage. The presence and elevation of lakes is vital for understanding local differences in diurnal cycles and the lag between maximum snow melt on spring days and maximum discharge at the gauges is a function of hypsometry and lake buffering. We discuss the importance of local differences in the timing of discharge for fjord nutrient supply, particularly during spring snow melt and evaluate the potential for using such a dataset for assessing hydrological decadal trends.