THE NASHWAAK-EXPERIMENTAL-WATERSHED-PROJECT - ANALYZING EFFECTS OF CLEARCUTTING ON SOIL-TEMPERATURE, SOIL-MOISTURE, SNOWPACK, SNOWMELT AND STREAM-FLOW

A forest disturbance such as clearcutting affects local climate condit ions by affecting surface reflectance, amount of snow catch, amount an d timing of snowmelt and stream water discharge, soil moisture, soil t emperature and soil frost. In this paper, snowpack water equivalents, soil moisture and soil temperature are simulated for pre- and post-har vest conditions at the Nashwaak Experimental Watershed Project. This P roject involved a paired watershed experiment, with one of the forest- covered basins cut by way of a conventional harvesting operation, and the other basin left as a control. The computer simulations involved t he application of a forest hydrology model (ForHyM) and a soil tempera ture model (ForSTeM). Both models used monthly amounts of rain and sno w and mean monthly air temperatures records as input. Forest-atmospher e energy balances were calculated for year-round conditions. In this r eport, special attention was given to the energy balance when the grou nd is covered with snow. Doing so generated a process-oriented approac h for calculating snowmelt throughout the winter and at the beginning of spring. Year-round model simulations for stream discharge were comp ared with pre- and post-harvest discharge observations. Also compared were simulated and observed snowpack water equivalents. Simulated resu lts were in good agreement with field observations, thereby supporting the general calculations made for pre-and post-harvest soil moisture, temperature and frost conditions. Altogether; it was found that clear cutting produced positive as well as negative contributions to the wat er budget of the harvested basin. Positive contributions were likely d ue to reduced evapotranspiration. Negative contributions were likely d ue to reduced snow and fog water catch. Increased ground-level insolat ion advanced the snowmelt season for the cut basin by about two weeks.