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 (SWEs) 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 39% and 27% in the clear-cut (reference = 144. mm and 121 mm) during 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 melt 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.