Abstract
Abstract. Central Chile is an economically important region for which water supply is dependent on snow- and ice melt. Nevertheless, the relative contribution of water supplied by each of those two sources remains largely unknown. This study represents the first attempt to estimate the region's water balance using stable isotopes of water in streamflow and its sources. Isotopic ratios of both H and O were monitored during one year in a high-altitude basin with a moderate glacier cover (11.5%). We found that the steep altitude gradient of the studied catchment caused a corresponding gradient in snowpack isotopic composition and that this spatial variation had a profound effect on the temporal evolution of streamflow isotopic composition during snowmelt. Glacier melt and snowmelt contributions to streamflow in the studied basin were determined using a quantitative analysis of the isotopic composition of streamflow and its sources, resulting in a glacier melt contribution of 50–90% for the unusually dry melt year of 2011/2012. This suggests that in (La Niña) years with little precipitation, glacier melt is an important water source for central Chile. Predicted decreases in glacier melt due to global warming may therefore have a negative long-term impact on water availability in the Central Andes. The pronounced seasonal pattern in streamflow isotope composition and its close relation to the variability in snow cover and discharge presents a potentially powerful tool to relate discharge variability in mountainous, melt-dominated catchments with related factors such as contributions of sources to streamflow and snowmelt transit times.
Highlights
1.1 Hydrology in the extratropical Andes region – unknown inputsKnowledge of the processes determining discharge in catchments dominated by glacier melt and snowmelt becomes increasingly important as population and industrial activity increase in regions dependent on these water sources
We aimed to explore how episodic changes in isotope composition, along with meteorological and discharge data, can be combined to understand the hydrological processes occurring in semi-arid mountainous catchments, such as groundwater storage and precipitation events
In order to visualise the approximate contribution of snowmelt to runoff compared to glacier melt, we plotted maximum winter snow water equivalent (SWE) measured at the snow pillow at Portillo, against area-specific runoff from the Juncal River measured at Juncal River basin (Junc) (Fig. 4)
Summary
1.1 Hydrology in the extratropical Andes region – unknown inputs. Knowledge of the processes determining discharge in catchments dominated by glacier melt and snowmelt becomes increasingly important as population and industrial activity increase in regions dependent on these water sources. Meteorological and hydrological conditions are similar to many semi-arid, mountainous regions of the world; extremely low precipitation during the summer months results in snowmelt and glacier melt from high altitudes being the main sources of streamflow (Cortes et al, 2011; Garreaud et al, 2009; Pellicciotti et al, 2005). The processes governing accumulation and melt of snow and ice at high elevations in the extratropical Andes remain difficult to quantify and model. It is probably true that melt from the seasonal snowpack accounts for the bulk of runoff in the region (Masiokas et al, 2006; Pena and Nazarala, 1987), the contribution of glacier melt to the hydrologic regime remains a key component of the hydrologic cycle considering that (1) many
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