Trends in Canadian temperature and precipitation during the 20th century are analyzed using recently updated and adjusted station data. Six elements, maximum, minimum and mean temperatures along with diurnal temperature range (DTR), precipitation totals and ratio of snowfall to total precipitation are investigated. Anomalies from the IntroductionRecent analyses of climate trends indicate that the global mean surface temperature has increased by about 0.3 to 0.68C since the late 19th century, and by about 0.2 to 0.38C over the last 40 years (e.g., Nicholls et al., 1996). These studies have also shown that daily minimum temperatures have often increased at a greater rate than maximum temperatures, resulting in a decrease in the diurnal temperature range (DTR) for several regions of the world. There has been a small positive trend in global precipitation, of about 1% during the 20th century over land, with a greater increase in the high latitudes of the Northern Hemisphere, especially during the cold season. Considerable spatial and temporal variations have occurred over the past 100 years, and these tendencies of warming, increased precipitation and reduction of DTR have not been globally uniform. For example, Nicholls et al. (1996) showed warming in the mid-latitude Northern Hemisphere continents in winter and spring, and year-round cooling in the northwest North Atlantic and mid-latitudes over the North Pacific in the past four decades. Understanding the observed climate trends

Abstract. This study presents trends computed for the past 30-50 years for 11 hydroclimatic variables obtained from the recently created Canadian Reference Hydrometric Basin Network database. It was found that annual mean streamflow has generally decreased during the periods, with significant decreases detected in the southern part of the country. Monthly mean streamflow for most months also decreased, with the greatest decreases occurring in August and September. The exceptions are March and April, when significant increases in streamflow were observed. Significant increases were identified in lower percentiles of the daily streamflow frequency distribution over northern British Columbia and the Yukon Territory. In southern Canada, significant decreases were observed in all percentiles of the daily streamflow distribution. Breakup of river ice and the ensuing spring freshet occur significantly earlier, especially in British Columbia. There is also evidence to suggest earlier freeze-up of rivers, particularly in eastern Canada. The trends observed in hydroclimatic variables are entirely consistent with those identified in climatic variables in other Canadian studies.

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The goal of this project was to develop adjustment procedures to use daily resolution data to generate high quality time series of precipitation and to perform regional trend analyses on the resulting datasets. A total of 69 locations, most with data covering the period 1900-96 were used. Data availability in much of the Canadian Arctic was restricted to 1948-96. By using daily data, improved corrections to precipitation data

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computed the mean annual basin temperature (T) to be -3.4°C, the mean annual basin precipitation (P) to be 421 mm and the mean annual basin evapotranspiration (E) to be 277 mm. A simple water balance was applied to test the consistency of the P and E fields with the observed basin discharge (Q). For the 24-year period 1972 to 1995, the mean annual residual (P-E-Q) for the water balance was -28.4 mm. This residual is a combination of errors in the three water balance components and the assumption of zero annual storage. It is within the estimation errors associated with the measurement and analysis methods used. Further analysis on the correlation of Q with the total basin net surface moisture supply (P-E) showed that P and (P-E) are most strongly correlated with Q with a 3-month lag, i.e., a discharge water-year of October-September corresponds best with a (P-E) year of July-June. In examining the seasonal correlation of T and E with Q, we found that summer T was significantly correlated with annual Q but there was no significant correlation between any seasonal E or annual Q. This suggests that although the Morton model estimates of E provided a reasonable magnitude for the long-term annual basin water balance, it cannot be considered reliable for year-to-year or shorter-term estimates of the basin evapotranspiration. In examining the 1994/95 water year, it was found to be the lowest discharge year (October-September) in the observed record. This is consistent with the 3-month lagged climate data year (July-June) which for 1994/95 has the largest (P-E) anomaly; it is also the driest year since 1950 having the warmest summer months on record and the third lowest precipitation on record.To demonstrate a practical application of the climate datasets generated by this study, we constructed a multilinear regression model for annual (October-September)