Surface Temperature and Humidity Trends in Canada for 1953–2005

Abstract

Annual and seasonal trends in temperature, dewpoint, relative humidity, and specific humidity are presented for the period 1953-2005. The analysis uses hourly observations from 75 climatological stations across Canada. Data were examined for discontinuities due to changes in instruments and observing practice. It was found that the main discontinuity corresponds to the replacement of the psychrometer by the dewcel in the early 1970s, which created an artificial negative step in relative humidity and dewpoint at many locations. After accounting for these discontinuities, the results of trend analysis show evidence of an increase in air moisture content associated with the warming observed in the country. During winter and spring, the significant warming in the western and southern regions is accompanied by an increase in dewpoint and specific humidity and by a decrease in relative humidity; in summer, warming is observed in the southeast and it is associated with significant positive trends in dewpoint and specific humidity. Although there is no strong evidence of a greater nighttime warming in Canada over 1953-2005, the nighttime dewpoint and specific humidity trends are slightly larger than the daytime trends, especially during the spring and summer.

Observed Trends in Severe Weather Conditions Based on Humidex, Wind Chill, and Heavy Rainfall Events in Canada for 1953–2012

“…4d). The significant decreasing trends in the number of days with wind chill are consistent with the significant increasing trends in winter mean temperature (Vincent et al, 2007) and significant decreasing trends in near-surface wind speed (Wan et al, 2010) observed mainly in western and southern regions of the country.…”

“…There have been significant increases in HX > 35 and HX > 40 at fewer stations, and these are located mainly in southern Ontario. The significant increasing trends in the number of days with humidex are consistent with the significant increasing trends seen in summer mean temperature and summer mean dew point, mainly for locations in British Columbia and eastern regions of Canada (Vincent et al, 2007).…”

“…If the dew point temperature was higher than the dry bulb temperature, it was estimated from the dry bulb temperature (only a few corrections were needed). A homogeneity assessment of hourly dry bulb and dew point temperatures was carried out by Vincent et al (2007) with little evidence of detectable inhomogeneities resulting from station relocation or changes in observing practices. Quality assurance was applied to the TBRG hourly raingauge data, which included similar approaches with more options for internal consistency checks using a collocated higher precision MSC Type B standard rain gauge with daily observations.…”

Trends of surface humidity and temperature during 1951−2012 in Beijing, China

“…As in situ observations of surface humidity can be easily influenced by changes of instruments and observation procedures (Dai, 2006), the simplified Clausius-Clapeyron equation (C-C equation) is recommended for practical convenience. Based on the C-C equation, the saturation vapour pressure over pure water will increase about 6.577gkg -1 , but global-scale and the regional-scale studies indicate that there are slight differences between in situ observations and theoretical values (Dai, 2006;Vincent et al, 2007;Brown et al, 2013). Hence, estimating the parameters of the formula is essential before analysing the trends of surface humidity at local scale.…”

Cloud type observations and trends in Canada, 1953–2003

“…For the sake of brevity, in the discussion of the results 'hours per 51 years' are used, which implicitly means 'hours per year per 51 years'. The trends are presented over the 51-year period for compatibility with a previous cloud study (Milewska, 2004) and other related Canadian studies of trends in temperature, climate indices, and humidity that were performed for approximately the same time period (Zhang et al, 2000;Vincent and Mekis, 2006;Vincent et al, 2007).…”