Homogenized Surface Air Temperature Data

This website provides monthly, seasonal and annual means of the daily maximum, minimum and mean temperatures from the Second Generation of Homogenized Temperature datasets which now replace the first generation datasets.

A First Generation of Homogenized Temperature datasets were originally prepared for climate trends analysis in Canada. Non-climatic shifts were identified in the annual means of the daily maximum and minimum temperatures using a technique based on regression models (Vincent, 1998). The shifts were mainly due to the relocation of the station, changes in observing practices and automation (Vincent and Gullett, 1999). Adjustments for the identified shifts were applied to monthly and daily maximum and minimum temperatures (Vincent et al. 2002). Observations from nearby stations were sometimes combined to create long time series that are useful for climate change studies.

The Second Generation of Homogenized Temperature datasets were recently prepared to provide a better spatial and temporal representation of the climate trends in Canada. In this new version, the list of stations was revised to include stations with long-term temperature observations covering as many of the recent years as possible. New adjustments were applied to the daily minimum temperatures in order to address the bias due to a change in observing time (Vincent et al. 2009). Techniques based on regression models were used to detect non-climatic shifts in temperature monthly series (Wang et al. 2007; Vincent 1998). A new procedure based on a Quantile-Matching (QM) algorithm was applied to derive adjustments (Vincent et al., 2012; Wang et al. 2010).

Questions and comments can be sent to AHCCD@ec.gc.ca.

Reference to the second generation homogenized temperature

Vincent, L. A., X. L. Wang, E. J. Milewska, H. Wan, F. Yang, and V. Swail , 2012. A second generation of homogenized Canadian monthly surface air temperature for climate trend analysis, J. Geophys. Res., 117, D18110, doi:10.1029/2012JD017859.

Further references

Vincent, L.A., E.J. Milewska, R. Hopkinson and L. Malone, 2009: Bias in minimum temperature introduced by a redefinition of the climatological day at the Canadian synoptic stations. Journal of Applied Meteorology and Climatology, 48, 2160-2168. DOI: 10.1175/2009JAMC2191.1.

Vincent, L.A., X. Zhang, B.R. Bonsal and W.D. Hogg, 2002: Homogenization of daily temperatures over Canada. Journal of Climate, 15, 1322-1334.

Vincent, L.A., and D.W. Gullett, 1999: Canadian historical and homogeneous temperature datasets for climate change analyses. International Journal of Climatology, 19, 1375-1388.

Vincent, L.A., 1998: A technique for the identification of inhomogeneities in Canadian temperature series. Journal of Climate, 11, 1094-1104.

Wang, X. L., H. Chen, Y. Wu, Y. Feng, and Q. Pu, 2010: New techniques for detection and adjustment of shifts in daily precipitation data series. J. Appl. Meteor. Climatol., 49, 2416-2436. DOI: 10.1175/2010JAMC2376.1

Wang, X. L., Q. H. Wen, and Y. Wu, 2007: Penalized maximal t test for detecting undocumented mean change in climate data series. J. Appl. Meteor. Climatol., 46 (No. 6), 916-931. DOI:10.1175/JAM2504.1