Assigned Session: FS 3.122: The status and future of mountain waters
Snow droughts in the extratropical Andes Cordillera: perspective from 60-year physically based hydrological modelling
Abstract ID: 3.12532 | Accepted as Talk | Talk | TBA | TBA
Diego Hernandez (1)
James McPhee (2), Maria Courard (2), Alonso Mejías (2), Zelalem Tesemma (3), Mohamed Ismaiel Ahmed (4), Alain Pietroniro (4), John Pomeroy (5)
(2) University of Chile, Santiago, Chile
(3) Environment Canada, Saskatoon, Canada
(4) University of Calgary, Calgary, Canada
(5) University of Saskatchewan, Saskatoon, Canada
Snow accumulation is the paramount water reservoir in the high mountains, sustaining extensive hydro-socio-ecological systems downstream. The hydroclimate of the extratropical Andes is highly variable on the interannual scale, with several modes of natural variability contributing to the behaviour of large-scale precipitation and ultimately determining the spatio-temporal variability of snow accumulation. Starting in 2010, these teleconnections were disrupted by the so-called Chile megadrought which perturbed the water supply of the country. Large snow drought analyses typically rely on coarse-scale outputs that often fail to represent local processes, and data-driven approaches may not capture the complex interplay between precipitation, temperature and runoff generation. To improve understanding at the relevant scales, we calibrate the physically based hydrological model MESH, which has been implemented in cold regions where steep slopes and cryospheric processes are important. For five Andean basins along an arid-humid gradient, we explore the hydrological implications of snow droughts within the 1961-2020 water years by classifying them as dry, warm or dry-and-warm types and presenting the spatial patterns of changes in key snow and water variables. Our results show a shift towards dry-and-warm snow droughts in central Chile: the megadrought is almost exclusively dry-and-warm. The deficits during the megadrought progressively amplify from total to solid precipitation and to snow accumulation at the end of winter. Less snow, more evaporation and less runoff scaled by annual precipitation (i.e., efficiencies) compound the drought propagation after 2010, which shows the largest streamflow deficit compared to snow droughts before 2010. For snow droughts before 2010, the release from soil and especially from groundwater storage mitigates the translation from water availability to streamflow deficits. Furthermore, the attribution experiment indicates that precipitation rather than temperature anomalies explain the drought propagation in this domain. These past snow droughts provide a glimpse into the future climate under the most likely emission scenarios, as the projected precipitation deficits are strikingly similar. This study is important for informing preparedness strategies as climate change continues to disrupt historical patterns of streamflow generation in the high mountain region and the lowland areas that depend on it.
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