Hydrological Effects of Clear-Cutting in a Boreal Forest - Snowpack dynamics, Snowmelt and Streamflow Responses

We investigated the effects of forest clear-cutting on snow accumulation, melt dynamics and associated stream responses in a paired catchment experiment in northern Sweden. Two boreal first-order streams, of which one was clear-cut harvested in 2006, were compared during the 2005-2011 study period. Clear-cutting increased snow accumulation expressed as snow water equivalents (SWE) on average by 29 mm (27%). Further snow melt occurred earlier in the clear-cut resulting in more rapid stream responses of the harvested catchment during some, but not all years (2008, 2009 and 2010). Snowmelt runoff increased by 55mm and 33mm in the clear-cut (reference= 144 mm and 121 mm) during the years 2008 and 2009, respectively, whereas no significant difference in runoff was observed during spring 2010 and 2011. The results indicate that stream responses to snowmelt primarily governed by sensible heat transfer through air temperature, radiation and turbulent heat fluxes are controlled by three main processes: i) interception in the forest canopy, reducing SWE; ii) sublimation directly from the snowpack, and iii) additional losses of soil water as, for example, evaporation during the melt. The year-to-year variation in these processes determines the stream response to clear-cutting during snowmelt. Overall this study underlines the large inter-annual variation in spring snowmelt responses of managed boreal catchments, which may have hydrological and biochemical implications for downstream locations. Detailed analysis of the 2010 Snowmelt: The upper panel shows stream discharge (Q) and air temperature (Ta) of the CC-4 (clear-cut) as well as the NR-7 (northern reference) catchment, respectively. The lower panel shows snow water equivalents (SWE) of the snowpack during the spring 2010 measured within NR-7 and CC-4. Error bars of snow core measurements represent standard deviations, snow core sample sizes are n=10 for all small scale SWE measurements.