Trends in Canadian streamflow

This study presents trends computed for the past 30-50 years for 11 hydrocl imatic variables obtained from the recently created Canadian Reference Hydr ometric Basin Network database. It was found that annual, mean streamflow h as generally decreased during the periods, with significant decreases detec ted in the southern part of the country. Monthly mean streamflow for most m onths also decreased, with the greatest decreases occurring in August and S eptember. The exceptions are March and April, when significant increases in streamflow were observed. Significant increases were identified in lower p ercentiles of the daily streamflow frequency distribution over northern Bri tish Columbia and the Yukon Territory. In southern Canada, significant decr eases were observed in all percentiles of the daily streamflow distribution . Breakup of river ice and the ensuing spring freshet occur significantly e arlier, especially in British Columbia. There is also evidence to suggest e arlier freeze-up of rivers, particularly in eastern Canada. The trends obse rved in hydroclimatic variables are entirely consistent with those identifi ed in climatic variables in other Canadian studies.