Precipitation data quality and long-term water balances within the Moose River Basin, east-central Canada

Annual water balance time series (precipitation, runoff, evaporation) for s ub-basins in the southern portion of the Moose River Basin (MRB) of northea stern Ontario and western Quebec previously suggested that both annual evap oration and precipitation increased by similar to2 mm y(-1) during the 1918 -1994 period. However, summer air temperature data were not consistent with evaporation increases of that magnitude. Suspected inhomogeneities (i.e., non-climatic steps or trends associated with changes in measurement procedu re or site exposure) in precipitation records for the MRB region indicated significant underestimation of annual precipitation prior to 1950. Temporal trends in rehabilitated precipitation datasets obtained from the Meteorolo gical Service of Canada revealed that annual precipitation was essentially constant during the 1918-1994 period in the MRB, after several inhomogeneit ies were accounted for. This contradicts previously reported increases in p recipitation for the region, and results indicate that streamflow time seri es from large river basins can assist assessment of the validity of apparen t precipitation trends. Although there were no trends in long-term annual p recipitation and runoff records, preliminary analyses revealed trends at th e seasonal scale. In particular, decreased annual snowfall was offset by in creased annual rainfall, which is broadly consistent with predicted impacts of climate warming. Annual evaporation appears to have been relatively con stant in the southern MRB during the 1918-1994 period, despite changes in t he partitioning of precipitation between rain and snow and the seasonal tim ing of precipitation, and slight increases in summer daytime air temperatur es.