130: UHI #3 - Perth (Western Australia)

The population of Western Australia is only about 2.67 million but two million of that total live in the state capital Perth. So 75% of the state's population live in Perth even though Perth accounts for less than 0.25% of the area of Western Australia. Perhaps this is why temperatures in Perth appear to have risen at more than twice the rate of the rest of the state. By 1990 temperatures in Perth had risen more than 1.5°C since 1900 compared to less than 0.7°C in Western Australia as a whole (see Fig. 130.1 below). That looks like classic urban heat island (UHI) behaviour. The only caveat is that the main weather station for Perth at Perth Regional Office (Berkeley Earth ID: 4321) ceased operations in 1992 just as the UHI was taking off.

Fig. 130.1: The change to the 5-year average temperatures of Perth (red curve) and Western Australia (blue curve) since 1900.

In Post 22 I examined the temperature trends for Western Australia. The mean temperature change since 1900 is shown in Fig. 130.2 below and it indicates that Western Australia has warmed by about 1°C since 1990. The best fit for 1991-1990 indicates a temperature rise of less than 0.64°C in 90 years while the 5-year average suggests a rise of about 0.67°C for the same period.

Fig. 130.2: The mean temperature change for Western Australia since 1900 relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1901 to 1990 and has a positive gradient of +0.71 ± 0.11 °C per century.

The mean temperature anomaly (MTA) for Western Australia shown in Fig. 130.2 above is the result of averaging monthly temperature anomalies from nearly hundred stations as Fig. 130.3 below demonstrates (see here for a full list of all stations). However, before 1900 there are less than ten available stations so the MTA is less reliable and more prone to error from statistical variability. For more details and analysis of the complete data for Western Australia see Post 22.

Fig. 130.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Western Australia in Fig. 130.2.

The oldest weather station in Western Australia is Perth Regional Office (Berkeley Earth ID: 4321). It has data stretching back as far as 1852, and continuous data from 1876 to 1992. In fact it is the only station within Perth with over 480 months of continuous data between 1876 to 1992, hence its significance as a case study of the urban heat island (UHI) effect.

Compared to the rest of Western Australia, Perth Regional Office shows much more significant and continuous warming since 1900 (see Fig. 130.3 below). The best fit for 1901-1990 indicates a temperature rise of more than 1.47°C in 90 years while the 5-year average suggests a rise of over 1.5°C.

Fig. 130.4: The mean temperature change for Perth Regional Office since 1900 relative to its 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1901 to 1990 and has a positive gradient of +1.63 ± 0.19 °C per century.

Summary

The following temperature changes were observed from 1901 to 1990.

Western Australia: 0.67°C (trend 0.64°C).

Perth: 1.53°C (trend 1.47°C).

So Perth warmed by almost 1°C more than the surrounding state of Western Australia in the ninety years up to 1990, or more than twice as fast. A classic UHI!