Published data were used to analyse the long-term annual temperature trends at twelve locations located in Japan and one in Korea. Similarities in the trends for individual stations enabled a comprehensive trend to be established for the whole region.
The data used were all from the website of KNMI (the Royal Netherlands Meteorological Institute). Only raw data were used (ie as originally recorded, without any adjustments). Data were only used from stations located in rural areas or in small towns so as to avoid the possible influence of urbanisation on the temperatures.
The periods of the data ranged from 77 years to 135 years of complete annual data. The earliest record, at Nemuro, commenced in 1880.
The plots shown below are of the annual mean temperatures at each of the twelve locations. On each plot a polynomial “best fit” trendline has been added. It should be noted that the trendlines near each extremity (ie near the start and end of the records) are quite sensitive to individual data points, whereas trendlines within the main body of the record are much more stable and reliable.
COMPARISON OF TRENDLINES
Annual Mean Temperature Trends
[ The basis of these trendlines can be seen from the analyses for the twelve individual stations – see next section ]
Annual Mean Temperature Residual Trends
[ The individual trend-lines have been adjusted by constant amounts to be approximately zero at trend troughs around 1910-1920 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Ishigakijima (Japan) 1897-2015
Naze (Japan) 1897-2015
Izuhara (Japan) 1886-2015
Wajima (Japan) 1930-2015
Shionomisaki (Japan) 1913-2015
Omaezaki (Japan) 1932-2015
Hachijojima (Japan) 1906-2015
Suttsu (Japan) 1887-2015
Urakawa (Japan) 1927-2015
Nemuro (Japan) 1880-2015
Abashiri (Japan) 1890-2015
Ullungdo (Korea) 1938-2015
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for the twelve stations are similar.
- A well-defined cyclical pattern in the trend-line is apparent at all of the stations. Lows occurred in around 1910-1920 and around 1950, and Highs occurred around 1970 and around 2010.
- The ~1950 “High” was generally about 0.3-0.5 deg C higher than the “Low” in ~1910.
- The ~1970 “Low” was generally about 0.5 deg C higher than the “Low” in ~1910.
- The ~2010 “High” was generally about 1.0-1.5 deg C higher than the “Low” in ~1910.
- The consistency of the annual mean temperature trend-lines of the twelve widely separated stations provides support for the good quality of the data and the conclusions drawn from the analysis.
- There is evidence of temperature rises of around 1.0-1.5 deg C since 1950, but that a cyclical peak occurred around 2010.
This article was written by Brian Gunter of Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.