Modeling increases in snowmelt yield and desynchronization resulting from forest gap-thinning treatments in a northern mountain headwater basin

• Published in: Water resources research 2013-02, Vol.49 (2), p.936-949
• Main Authors: Ellis, C. R., Pomeroy, J. W., Link, T. E.
• Format: Article
• Language: English
• Subjects: Clearcutting; Cold regions; forest; Forests; mountain; Mountain forests; Mountain regions; Mountains; Radiation; Sensitivity analysis; Slopes; Snow accumulation; Snowmelt; Spring; Sublimation; Thinning
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/wrcr.20089

Key Points Forest thinning treatments in mountain regions may substantially alter snowmelt Changes in snowmelt timing from forest thinning depend on slope and aspect. Changes in snowmelt timing are caused primarily by shifts in radiation to snow. A physically based model built upon extensive field observations of radiation dynamics and snow processes in cold regions forest environments was used to investigate the impacts of prescribed forest gap‐thinning treatments on spring snowmelt in a small Saskatchewan River headwater basin of the Canadian Rocky Mountains. Both field observations and model simulations showed that snow accumulations in small clear‐cut gaps was roughly double those under intact forest cover due to sublimation losses from the canopy. Consequently, mountain forests thinned with small clear‐cut gaps resulted in a substantial increase in the magnitude of spring snowmelt. However, the impact of forest thinning on the timing of snowmelt was highly dependent on slope orientation; thinning accelerated snowmelt on south facing slopes primarily through enhanced shortwave radiation, but retarded snowmelt on north facing slopes primarily through reduced incoming longwave radiation. As a result, thinning treatments across opposing north facing and south facing mountain slopes acted to substantially expand the spring melt period in the basin, and illustrated the important hydrological control imparted by intact forest cover through its synchronization of snowmelt across complex terrain. A sensitivity analysis of snowmelt timing to varying spring meteorological conditions strongly suggests that shifts in spring snowmelt runoff from similar forest thinning treatments in mountain regions will depend on the slope and aspect at which they occur in combination with the seasonal timing of snowmelt resulting from latitude‐controlled solar elevation effects.