Abstract
Abstract. As climate change is projected to alter both temperature and precipitation, snow-controlled mid-latitude catchments are expected to experience substantial shifts in their seasonal regime, which will have direct implications for water management. In order to provide authoritative projections of climate change impacts, the uncertainty inherent to all components of the modelling chain needs to be accounted for. This study assesses the uncertainty in potential impacts of climate change on the hydro-climate of a headwater sub-catchment of New Zealand's largest catchment (the Clutha River) using a fully distributed hydrological model (WaSiM) and unique ensemble encompassing different uncertainty sources: general circulation model (GCM), emission scenario, bias correction and snow model. The inclusion of snow models is particularly important, given that (1) they are a rarely considered aspect of uncertainty in hydrological modelling studies, and (2) snow has a considerable influence on seasonal patterns of river flow in alpine catchments such as the Clutha. Projected changes in river flow for the 2050s and 2090s encompass substantial increases in streamflow from May to October, and a decline between December and March. The dominant drivers are changes in the seasonal distribution of precipitation (for the 2090s +29 to +84 % in winter) and substantial decreases in the seasonal snow storage due to temperature increase. A quantitative comparison of uncertainty identified GCM structure as the dominant contributor in the seasonal streamflow signal (44–57 %) followed by emission scenario (16–49 %), bias correction (4–22 %) and snow model (3–10 %). While these findings suggest that the role of the snow model is comparatively small, its contribution to the overall uncertainty was still found to be noticeable for winter and summer.
Highlights
Over recent decades climate change has had a considerable impact on the Earth’s freshwater resources (Jiménez Cisneros et al, 2014), causing, amongst others, changes in the amount of runoff (Piao et al, 2010), the timing of peak discharge (Hidalgo et al, 2009), a reduction in glacier volume (Rosenzweig et al, 2007) and an increase in flood risk (Pall et al, 2011)
The regimes of the eight RCMdriven simulations of each sub-ensemble were compared to the observed runoff regime (OBS) and the modelled runoff regime forced by the observed meteorology (MODMETEOOBS)
Overall the linear transformation (LT) method shows a lower skill in reproducing the observed regime, which is especially pronounced in combination with temperature index (Tindex)
Summary
Over recent decades climate change has had a considerable impact on the Earth’s freshwater resources (Jiménez Cisneros et al, 2014), causing, amongst others, changes in the amount of runoff (Piao et al, 2010), the timing of peak discharge (Hidalgo et al, 2009), a reduction in glacier volume (Rosenzweig et al, 2007) and an increase in flood risk (Pall et al, 2011). Future impacts under mid- and late 21st century climate change are projected to intensify, affecting both the main processes and stores of the water cycle. The impacts include an increase of potential evapotranspiration (PET) over most land areas, a further shrinkage of glaciers and changes in the runoff regime of snowmelt-affected basins (Jiménez Cisneros et al, 2014). 21st century climate change is expected to have substantial implications for water users and operators alike, which makes robust projections of potential changes in the seasonality and magnitude of streamflow essential. Climate change impact studies typically use a cascade of models and processing steps to move between the scales of the lower resolution
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