( Revised 17 November 2017 with addition of Nakhon Sawan )
Published data were used to analyse the long-term annual temperature trends at eight locations located in Thailand, Malaysia and Philippines. 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 62 years to 107 years of complete annual data. The earliest record, at Sandakan, commenced in 1880.
The plots shown below are of the annual mean temperatures at each of the eight 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 eight 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 an trend minimum around 1970. ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Nakhon Sawan (Thailand) 1939-2016
Sitiawan (Malaysia) 1931-2015
Kota Bharu (Malaysia) 1930-2015
Sandakan (Malaysia) 1880-2014
Iliola (Philippines) 1903-2010
Legaspi (Philippines) 1903-2015
Dagupan (Philippines) 1903-2015
Aparri (Philippines) 1887-2015
DISCUSSION AND COMMENTS
- The data analysed were limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for the eight stations are similar.
- A well-defined cyclical pattern in the trend-line is apparent at all of the stations. Lows occurred in around 1900 and around 1970, while Highs occurred around 1930 and around 2000.
- Four of the stations showed well-defined cyclical Highs around 2000.
- The ~2000 “High” was generally about 0.5 deg C higher than that in ~1930.
- The ~1970 “Low” was generally about 0.3 deg C lower than the “High” in ~1930.
- The temperatures at the High around 1930 were around 0.5 deg C higher than in 1900.
- The consistency of the annual mean temperature trend-lines of the eight 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 0.5-0.8 deg C between around 1970 and 2000, but temperatures have generally stabalised or reduced since then..
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.