Reliability of results and conclusions based on statistical analysis of hydrological data in land-use hydrology

Forest managers require answers to basic hydrological questions for operational planning of timber harvesting activities in consumptive use watersheds in the Nelson Forest Region of British Columbia. Considerable documented evidence indicates that forest cover removal results in increased snow accumulation in cutblocks and causes water yield increases in streamflow but the magnitude of such effects is highly variable. A selection of relevant case studies are examined, statistical tests applied to original data and conclusions drawn. Peak snow water equivalent increases in clearcuts relative to the forest are generally substantial but best described by linear regression equations, rather than average percentages that are highly variable. Annual and monthly streamflow increases have been obtained via paired watershed experiments but some decreases have also been observed.