Abstract
Abstract. Glacierised catchments show a discharge regime that is strongly influenced by snow and glacier meltwaters. In this study, we modelled the mass balance and discharge rates for three highly glacierised catchments (>50% glacier cover) in western Norway over the period 1961–2012. The spatial pattern of the catchments follows a gradient in climate continentality from west to east. The model input were gridded temperature and precipitation values from seNorge (http://senorge.no) which are available at daily resolution. The model accounted for accumulation of snow, transformation of snow to firn and ice, evaporation and melt. Calibration and validation were performed for each catchment based on measurements of seasonal glacier mass balances and daily discharge rates, as additional validation data served daily melt rates from sonic rangers located in the ablation zones of two of the glaciers. The discharge sources snowmelt, glacier melt and rain were analysed with respect to spatial variations and temporal evolution. Model simulations reveal an increase in the relative contribution from glacier melt to total discharge for the three catchments from less than 10% in the early 1990s to 15–30% in the late 2000s. The decline in precipitation by 10–20% in the same period was therefore overcompensated, resulting in an increase in annual discharge by 5–20%. Annual discharge sums and annual glacier melt are most strongly correlated with annual and winter precipitation at the most maritime glacier and, with increased climate continentality, variations in both glacier melt contribution and annual discharge are becoming more strongly correlated with variations in summer temperatures. Therefore, glaciers in more continental climates are especially vulnerable to decrease in both annual and summer discharge with continued rise in summer temperatures and subsequent decrease in glacier extent. This may lead to significant changes to the discharge regime, with increase during spring but decline later in the year, especially for catchments in less maritime climate conditions.
Highlights
Meltwater constitutes a larger contribution to annual discharge than rain (Jost et al, 2012)
In this study annual discharge series for the past five decades were modelled for three glacierised catchments in Norway
The time series of modelled annual discharge were split up into their contributing water sources snowmelt, glacier melt and rain. Changes in these contributing sources during the modelling period were much larger than variations in annual discharge sums
Summary
Meltwater constitutes a larger contribution to annual discharge than rain (Jost et al, 2012). One sixth of the world’s population is dependent on water originating from snow or glacier melt (Hock et al, 2006). Assessment of meltwater runoff is crucial for both water supply and hydropower applications. Changes in discharge are connected to variations in either air temperature or precipitation or a combination of both. Future climatic and hydrological projections are subject to large uncertainties, ongoing climate change will result in major changes in both, timing and magnitude of the runoff regime. Glacier retreat and the release of freshwater are expected to be a key element in projections of discharge from glacierised catchments over the decades (e.g. Huss et al, 2010; Finger et al, 2012)
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