A crucial factor in analysis of long-term climate data is ensuring that the reporting station is able deliver a long-term record under the same conditions. In most locations, long-term data have unfortunately not been maintained. Meteorological stations have been relocated for a variety of reasons. Some have closed, and others have opened in a nearly location. The result is that interpretation of the data are required.
Where long-term data are available, another factor that influences records is physical changes at the reporting site. New buildings may increase shade, modify wind, and have minor but notable changes to rainfall patterns.
The Urban Heat Island effect relates to an increase in recorded temperatures in urban locations compared to that of the surrounding countryside due to the ability of the modified landscape (buildings and roads) to hold warmth and gradually radiate the heat back into the environment. The effect is more pronounced on the minimum temperatures, and has a seasonal factor.
A weather station has been maintained at Observatory Hill in Sydney, NSW, Australia since 1858. Five-year data series show no variation in the Rolling Five-year Annual Average rainfall, and a minor decline in the number of Days with Rain.
While there has been virtually no change in rainfall, there has been an increase in average temperature. This increase has been 2.7C in the minimum and 2.4C in the maximum. While the total temperature change caused by the Urban Heat Island can only be hypothesized, a study from Adelaide, SA, suggests it to be in the range of 2.0C.
Hottest days on record: 45.8C (18 Jan 2013); 45.3C (14 Jan 1938); 44.2 (1 Jan 2006); 43.4 (7 Jan 2014); 42.5 (13 Jan 1896).
Wettest days on record: 328mm (6 Jun 1986); 244mm (3 Feb 1990); 235mm (9 Nov 1984); 226mm (25 Feb 1873); 212mm (28 May 1889).
Based on the public domain data, it can be reasonably concluded that there is minimal evidence of climate change in Sydney.