Impact of glacier loss and vegetation succession on annual basin runoff

Abstract

Abstract. We use a simplified glacier-landscape model to investigate the degree to which basin topography, climate regime, and vegetation succession impact centennial variations in basin runoff during glacier retreat. In all simulations, annual basin runoff initially increases as water is released from glacier storage but ultimately decreases to below preretreat levels due to increases in evapotranspiration and decreases in orographic precipitation. We characterize the long-term (> 200 years) annual basin runoff curves with four metrics: the magnitude and timing of peak basin runoff, the time to preretreat basin runoff, and the magnitude of end basin runoff. We find that basin slope and climate regime have strong impacts on the magnitude and timing of peak basin runoff. Shallow sloping basins exhibit a later and larger peak basin runoff than steep basins and, similarly, continental glaciers produce later and larger peak basin runoff compared to maritime glaciers. Vegetation succession following glacier loss has little impact on the peak basin runoff but becomes increasingly important as time progresses, with more rapid and extensive vegetation leading to shorter times to preretreat basin runoff and lower levels of end basin runoff. We suggest that differences in the magnitude and timing of peak basin runoff in our simulations can largely be attributed to glacier dynamics: glaciers with long response times (i.e., those that respond slowly to climate change) are pushed farther out of equilibrium for a given climate forcing and produce larger variations in basin runoff than glaciers with short response times. Overall, our results demonstrate that glacier dynamics and vegetation succession should receive roughly equal attention when assessing the impacts of glacier mass loss on water resources.

Differences in the transient responses of individual glaciers: a case study of the Cascade Mountains of Washington State, USA

“…Figure 6a shows melt-flux changes following a trend in mass balance (and therefore specific melt), with L ( t ) given by the RB14 model for the idealized glaciers. M g peaks at t ~ τ for both glaciers (peaks are at 15 and 49 years), consistent with Carnahan and others (2019). The role of the response time is conceptually straightforward: for long τ , a slower initial retreat means specific melt anomalies can increase more before much melt area is lost, and the peak in M g is thus later than for short τ .…”

“…This phenomenon depends fundamentally on transient glacier dynamics. Carnahan and others (2019) showed that, over a wide range of parameters, the peak in simulated glacier-melt runoff occurred ~1 τ after the onset of a climate trend, using a metric for τ very similar to Eqn (1) (see Harrison and others, 2001).…”

Patterns in Microbial Assemblages Exported From the Meltwater of Arctic and Sub-Arctic Glaciers

“…One of the most conspicuous of the anticipated effects will be the altered production of meltwater (e.g., Milner et al, 2017;Huss and Hock, 2018), along with associated changes in hydrologic pathways (e.g., meltwater generated further inland and at greater elevations, intensifying connectivity between supra-and subglacial habitats), which ultimately have the greatest relevance for determining the quantity and character of solute and particulate fluxes. Yet, while the physical and chemical changes accompanying deglaciation may be comparatively straightforward to predict, the biological consequences for glacial ecosystems are far less intuitive (Fell et al, 2017;Hotaling et al, 2017a), and generalizations are inherently difficult to make due to differences in glacier size, elevation, bedrock, thermal regime, vegetation, and precipitation patterns (e.g., Carnahan et al, 2019). By studying microbial assemblages exported by glacier meltwater streams, it may be possible to investigate microbial processes taking place in the overall glacial system, and assess changes in structure and export over time.…”

Long-period variability in ice-dammed glacier outburst floods due to evolving catchment geometry

“…We model changes in glacier geometry with a onedimensional form of the shallow shelf approximation (SSA), which is a depth-and width-integrated flow model (Nick et al, 2009;Enderlin et al, 2013;Carnahan et al, 2019). For our simulations, we use a glacier with a simple bed geometry (a uniformly sloping bed with a slope of 4 • ) and assume a simple climate parameterization.…”