Ontario Climate Variations Bulletin – 2018

Ontario Climate Trends and Variations Bulletin – 2018

Ziwang Deng, Xin Qiu, Xiaolan Zhou, Huaiping Zhu*
LAMPS,Department of Mathematics and Statistics,York University
*Project Leader: Professor Huaiping Zhu

Summary: The Ontario provincial average temperature for 2018 (January to December) was 0.3°C below the baseline average (defined as the mean over the 1981–2010 reference period), ranking it the 37th warmest year observed since 1901, the 31st warmest since 1948 and the 23rd warmest since 1981. Although annual mean temperature is close to normal years, temperatures in some months are more extreme, and here are some examples,


The Climatic Research Unit (CRU) TS v. 4.02 data was used in this study.

  • Data Source:The gridded time-series used in this study can be found at DOI: http://doi.org/10/gcmcz3;
  • Temporal Coverage:This version, released 18 November 2018, covers the period 1901-2017
  • Spatial Coverage: All land areas (excluding Antarctica) at 0.5° resolution
  • Variables: tmp
  • Reference: Harris et al. (2014) doi:10.1002/joc.3711

The CFSv2 data for 2017-2018 was used to calculate temperature differences between 2018 and 2017

The Monthly Climate Summaries data was used for validation and station data analysis


(1) Calculate baseline average for reference period (1981-2010): monthly and annual average over CRU grid points within Ontario

(2) Calculate monthly and annual temperature anomaly for 2017 relative to the baseline averages (dT2017_ref)

(3) Calculate temperature difference between 2018 and 2017 (dT2018_2017) based on CFSv2 data

(4) Temperature anomaly for 2018 was estimated with equation:

dT2018_ref = dT2017_ref + dT2018_2017

(5) Calculate temperature difference between 2018 and 2017 (dT2018_2017)

(6) Carry out trend analysis and rank estimation for 2018 temperature. Rank represents the position of temperature of 2018 during the analysis period. For example, Jun (rank = 4) in Figure 2 indicates that the temperature in June 2018 is the 4th warmest June since 1981.

(7) Perform trend and rank analysis for three selected stations (i.e. Toronto, Ottawa and Geraldton), which have complete data.


Fig. 1 Ontario’s annual average temperature variation (1901-2018) based on CRU (1901-2017) and CFSv2 (2017-2018) data. 2018 value and the red line is the trend line from 1901 to 2018 (unit: °C).
Fig. 2 Ontario’s monthly average temperature variation for the period of 1981-2018; The horizontal dashed line represents the value in 2018 and the red line is the trend line from 1981 to 2018 (unit: °C; rank is for year 2018).
Fig. 3 Spatial variation of monthly average temperature anomalies for 2018 relative to the reference period 1981-2010(unit:°C).
Fig. 4 Toronto’s (79.6W, 43.7N) monthly average temperature variation during 1981-2018 (unit: °C; rank is for year 2018).
Fig. 5 Same as Fig. 4 but for Ottawa (75.7W,45.4N)
Fig. 6 Same as Fig.4 but for Geraldton (86.9W,49.8N)


[1]OCDP,2017,Historical and Projected climate Trends over Ontario





Prepared by LAMPS York University