The effect of storage on runoff from a headwater subarctic shield basin

Canadian Shield runoff production processes have been investigated, but res earch is needed beyond the hillslope scale to determine the influences on t he volume and timing of runoff from headwater basins to higher-order stream s. Such research will permit an understanding of the magnitude of climate c hange impacts at the watershed scale, where changes in the hydrologic regim e are felt most by water resource users. To this end, water budget terms we re measured over different portions of a headwater lake basin north of Yell owknife, Northwest Territories, during the spring snowmelt of 1998 to deter mine the relative importance of each component as water moved through the b asin. Evaporation made up 16% and runoff 70% of the snowmelt from upland ar eas. Upland pending of water during the melt increased the evaporative loss . Headwater lake storage deficits are very important in the timing and volu me of runoff that is transmitted downstream: 53% of basin meltwater went to meeting the storage deficit in the lake so that only 7% of the meltwater w as routed out of the basin. These results imply that topology of shield hea dwater basins, notably the location of lakes and antecedent water levels in lakes, are important in determining the runoff response. As storage defici ts in surface waters will cause changes over space in runoff response and t iming, it may be inappropriate to consider the snowpack or rainfall volume in isolation when forecasting runoff volume. These results are important fo r water management and hydrological modeling applications of northern shiel d basins.