Surface humidity and temperature trends in Canada for 1953–2004

Annual and seasonal trends in dewpoint, specific humidity, relative humidity and temperature are presented based on hourly observations from 75 climatological stations across Canada. Data were examined for possible discontinuities due to changes in observing procedures and instruments. It was found that the main cause of discontinuities correspond to the replacement of the psychrometer by the dewcel which has created artificial decreasing steps mostly in relative humidity. The annual and seasonal values were adjusted accordingly to provide better estimates of temporal changes over 1953-2004. Preliminary analysis of the trends shows some evidence of decreases in relative humidity and no consistent changes in specific humidity corresponding to the warming in temperature. These patterns are more pronounced in western Canada during the winter and spring.