Sensitivity of Snowmelt Hydrology on Mountain Slopes to Forest Cover Disturbance
Date
2011
Authors
Pomeroy, John W.
Fang, Xing
Ellis, Chad
Guan, May
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Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan
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Technical Report
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Abstract
Marmot Creek Research Basin was the subject of intense studies of snowmelt, water
balance and streamflow generation in order to generate a five year database of
precipitation inputs, snowpack dynamics and streamflow that could be used in
hydrological model testing. A physically based hydrological model of the basin was
constructed using the Cold Regions Hydrological Model and tested over four years of
simulation. The model was found to accurately simulate snowpacks in forested and
cleared landscapes and the timing and quantity of streamflow over the basin. The model
was manipulated to simulate the impacts of forest disturbance on basin snow dynamics,
snowmelt, streamflow and groundwater recharge. A total of 40 forest disturbance
scenarios were compared to the current land use over the four simulation years.
Disturbance scenarios ranged from the impact of pine beetle kill of lodgepole pine to
clearing of north or south facing slopes, forest fire and salvage logging impacts.
Pine beetle impacts were small in all cases with increases in snowmelt of less than 10%
and of streamflow and groundwater recharge of less than 2%. This is due to only 15% of
the basin area being covered with lodgepole pine and this pine being at lower elevations
which received much lower snowfall and rainfall than did higher elevations and so
generated much less streamflow and groundwater recharge. Forest disturbance due to
fire and clearing affected much large areas of the basin and higher elevations and were
generally more than twice as effective in increasing snowmelt or streamflow. For
complete forest cover removal with salvage logging a 45% increase in snowmelt was
simulated, however this only translated into a 5% increase in spring and summer
streamflow and a 7% increase in groundwater recharge. Forest fire with retention of
standing burned trunks was the most effect forest cover treatment for increasing
streamflow (up to 8%) due to minimizing both sublimation of winter snow and summer
evaporation rates. Peak daily streamflow discharges responded more strongly to forest
cover decrease than did seasonal streamflow with increases of over 20% in peak
streamflow with removal of forest cover. It is suggested that the dysynchronization of
snowmelt timing with forest cover removal resulted in an ineffective translation of
changes in snowmelt quantity to streamflow. This resulted in a complementary increase
in groundwater recharge as well as streamflow as forest cover was reduced. Presumably,
a basin with differing soil characteristics, groundwater regime or topographic orientation
would provide a differing hydrological response to forest cover change and the sensitivity
of these changes to basin characterisation needs further examination.
Description
Keywords
Snowmelt, Streamflow, Water balance, Hydrological modelling, Cold Regions Hydrological Model, Snowpack, Forest disturbance, Groundwater recharge, Mountain Pine Beetle, Marmot Creek, Alberta, Rocky Mountains
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Centre for Hydrology Report #10