Changes in glaciers in the Swiss Alps and impact on basin hydrology: Current state of the art and future research

Switzerland is one of the countries with some of the longest and best glaciological data sets. Its glaciers and their changes in response to climate have been extensively investigated, and the number and quality of related studies are notable. However, a comprehensive review of glacier changes and their impact on the hydrology of glacierised catchments for Switzerland is missing and we use the opportunity provided by the EU-FP7 ACQWA project to review the current state of knowledge about past changes and future projections. We examine the type of models that have been applied to infer glacier evolution and identify knowledge gaps that should be addressed in future research in addition to those indicated in previous publications. Common characteristics in long-term series of projected future glacier runoff are an initial peak followed by a decline, associated with shifts in seasonality, earlier melt onset and reduced summer runoff. However, the quantitative predictions are difficult to compare, as studies differ in terms of model structure, calibration strategies, input data, temporal and spatial resolution as well as future scenarios used for impact studies. We identify two sources of uncertainties among those emerging from recent research, and use simulations over four glaciers to: i) quantify the importance of the correct extrapolation of air temperature, and ii) point at the key role played by debris cover in modulating glacier response.