Mountain waters

Abstract/Description

The complex interactions between snow cover and forests have implications for mountain ecosystems and water resources. However, the geographic distribution of where snow and forest overlap in mountains remains poorly known. Here, we evaluate the importance of snowfall over forested environments and its spatial variability at the global scale and a high spatial resolution (0.1°), leveraging an existing climatological reanalysis and a satellite tree cover map. We find that most mountain ranges experience snowfall in forested areas, mostly in the northern hemisphere (7.7 10⁶ km²) and the southern Andes (0.3 10⁶ km²). The solid fraction of precipitation is generally greater in mountain forests of a basin than in the rest of it. This fraction reaches 64% locally, and 34% when aggregated over mountain ranges.

Abstract/Description

In western North America many watersheds that span the rain-snow transition zone are undergoing rapid changes in both land cover and rain-snow regime driven by forest operations and climate warming, respectively. A critical question in this region are how flow regimes are projected to change from these two drivers, both independently and in combination. The Distributed Hydrology Soil Vegetation Model (DHSVM) was used to address this question for projected rates of land cover and climate change across a range of scales for a snow-dominated watershed that is projected to shift from a snow to a rain-dominated hydroclimatic regime. The model was parameterized and tested with detailed data collected within the Mica Creek Experimental Watershed, a 28 km2 basin in the interior Pacific Northwest, USA. Streamflows were simulated for harvest rotations of 40 and 80 years to span the ranges of harvest intensities on private and public lands. At the smallest (~1 km2) scale, annual and low flows followed a typical trend of an initial increase followed by a decrease below baseline and gradual return to preharvest conditions. Peak flows remained elevated until canopy closure occurred after approximately 15 years followed by a return to baseline. At the largest (28 km2) scale, all flows were slightly elevated due to the active management regime that produced a landscape mosaic of stand ages. Projected flow changes based on 10 GCM outputs for RCP 4.5 and 8.5 emissions scenarios indicated slight increases in annual yields and peak flows, but relatively large declines in warm season low flows. Flow timing for an extreme case of 100% canopy removal resulted in a 12-day advance in the half-mass date, whereas for the most extreme emissions scenario the half mass date advanced by 56 and 69 days for mid- and late-century conditions, respectively. Canopy reduction due to harvest may therefore positively or negatively interfere with climate-driven flow changes depending on both watershed scale and species age diversity. Changes in flow timing are negligible relative to much stronger climate-driven changes resulting from a shift from a snow to rain-dominated hydrological regime.

Abstract/Description

Glacier and snow melt provide the majority of runoff in British Columbia’s Bridge River System, where water flows through three dams in succession to generate about 7% of the province’s hydroelectricity. Climate change-related glacier retreat and a reduction in seasonal snowpack threaten the reliability of late-summer reservoir inflows. Current operational hydrologic models do not account for glacier loss, posing challenges for long-term water resource planning.

To address this gap, we developed hydrologic models using the Raven modelling framework for the three watersheds supplying the Bridge River System. Using the Open Global Glacier Model, we simulated the evolution of 194 glaciers in the region through 2100 and incorporated projected glacier area changes into the hydrologic models to represent land cover evolution from 1985 to 2100.

Simulated future reservoir inflows and stream temperatures indicate an earlier freshet and earlier summer recession, with the greatest late-summer flow reductions occurring in the most glacierized basins. Observed stream temperature trends since 2013 demonstrate warming, and our projections indicate further increases of 3°C to 7°C by 2100. This study highlights the complexities of hydrologic modeling in remote, mountainous catchments with steep climatic gradients and presents novel methods for integrating land cover change and stream temperature estimation. Our findings will support future operational studies and reservoir temperature modeling in the watersheds, providing valuable insights into the system’s vulnerability to climate change.

Abstract/Description

Glacierized catchments are among the most rapidly changing and visibly affected regions worldwide due to glacier retreat and the associated loss of a critical water resource. This alters streamflow patterns, yet the timing and specific parts of the hydrograph that experience the strongest changes remain less understood. While previous studies have focused on glacio-hydrological modelling or observations of a small set of catchments, this study leverages a comprehensive dataset of streamflow observations from approximately 600 glacierized catchments (10–1000 km²) worldwide. By integrating these streamflow records with geodetic estimates of glacier mass loss, we identify regions experiencing the strongest mass losses and the associated rates of glacier change. Consequently, we explore the spatial and seasonal patterns of streamflow change and identify when the strongest streamflow changes occur and how they vary regionally and globally. For gauging stations with long-term observations (>50 years), we aim to assess whether emergence of specific seasonal trends and changes can be detected. Our findings highlight significant regional variability in the timing of the strongest seasonal streamflow changes. In some regions, late-summer flows show the most pronounced changes in relative magnitude, while in others, spring flows are most affected. By pinpointing these critical periods and spatial variability of change, this study provides insights into the downstream implications of glacier mass loss on water availability and streamflow dynamics.