CGRG Bibliography of Canadian Geomorphology
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Author : Bewley, D.W.; Alila, Y.; and Teti, P.
Date : 2008.
Title : Mountain pine beetle and topographic influences on landscape SWE variability.
Publication : Joint Annual Meeting of the Canadian Geophysical Union and the Canadian Geomorphology Research Group. May 11-14, Banff, Alberta.
Issue :
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Abstract
The Mountain Pine Beetle (MPB) epidemic is creating unprecedented large-scale forest disturbances across the central interior region of British Columbia, as mature pine forests are killed and salvage harvesting of these begin, and younger pine forests are now being attacked. While stand-level studies have now quantified the effect of these MPB forest covers on Snow Water Equivalent (SWE), the potential MPB changes to the hydrologic regime of a snowmelt-dominated watershed must consider all controls on SWE variability, including not only MPB disturbances but also topography and spatial snowfall distributions. The 1570 km2 Baker Creek watershed near Quesnel, British Columbia, represents a western tributary of the Fraser River affected by MPB, which was heavily instrumented during 2007 to measure a range of hydro-climatic variables between the stand and operationally-important watershed spatial scales. SWE measurements began in November 2007, at 12 survey plots incorporating a youngerattacked stand, mature-killed stand and clearcut at four different elevations between 910-1330m (covering 83% of the watershed), with sufficient within-plot measurements (N=36-56) to obtain reliable plot statistics for use in between-plot comparisons. The relief is sufficiently flat (mean slope 5.4°, s.d. 4.2°) to discard slope/aspect as an independent control of SWE variability. For each clearcut location, a nearby climate station (CS) provides half-hourly data on snow depth and 5 standard meteorological variables. Initial results indicate that the first major snowfall amount in November was within 10% at CS locations irrespective of location (= 40km apart) or elevation, but more subsequent melt and rain-onsnow events occurred lower down leading to increasing CS and plot-mean values of SWE with elevation (almost doubling between lowest and highest sites). Same-elevation SWE values between stands were similar, with young-attack:clearcut ratios of 0.75-1.16 (N=8) and mature-killed:clearcut ratios of 0.89-1.18 (N=6). This near-unity of ratio values was driven by canopy interception of snow in the forested stands, whereas in clearcuts up to 10% of snow depth was scoured during individual wind storms or lost due to sublimation over extended periods of sub-zero temperatures and calmer wind speeds. Both wind-driven and interception losses will be reduced in very young regenerating stands (=10 years old), and it is here that SWE may be maximized. During spring melt, SWE between elevations is expected to diverge further assuming initial melting lower down, and between same-elevation stands assuming clearcut snow melts faster. Continued SWE and hydrometeorological measurements will be used in conjunction with a distributed hydrological model to explore the relationship between melt patterns and spring freshet in 2008; subsequent attention will then focus on simulating the effects of various future harvesting scenarios on snow and discharge patterns, and how this translates into potential changes of flood frequency, magnitude and sediment fluxes.
Bibliography of Canadian Geomorphology