How the Climate in Melbourne Changed Over a Century

In the light of the ongoing heat wave in South Australia, we checked if the past 100 years reveal any significant changes in the local climate. For the analysis we used the Planet OS API and data from the Australian Bureau of Meteorology.

A record long heat wave has been torturing the southern states of Australia. We thought to look into the weather data for Melbourne, it’s second most populous city, to see if there are noteworthy signs of climate change. For the analysis we used over a 100 years of data provided by the Australian Bureau of Meteorology (BOM).

To make it easier to access and work with the large BOM datasets, we first added them to the Planet OS Datahub:

We focused on two main parameters — maximum temperature and precipitation data, and we used the third dataset from the list above.

From the graph below and the more in-depth analysis in the notebook, you can see the changes in the mean annual maximum temperature in Melbourne. The overall average, 20.03°C for the period of 1911–2017 is marked with a red dotted line and the green line marks a trend.

We checked if the El Niño–Southern Oscillation (ENSO) has had any impact on the area, and discovered that during a vast majority of the El Niño years, the temperatures were higher than the overall average. Meaning that it has indeed been affecting Melbourne.

Overall average for 1911–2017 is marked with red line, the trend with a green line.

We also discovered that the mean annual temperature has been rising over the past decades, especially after the year 2000. Ever since then, the temperature has dropped below average only once, in 2004. In 2007 and 2014 the temperature was a record 1.5 degrees above overall average that is certainly an unusual pattern.

Just as important as the change in the temperature is what has happened to the rainfall in Melbourne. During our analysis, we found out that the average amount of rainfall has been constantly decreasing over the past century. Less rainfall increases the risk of bushfires, impacts the agriculture in Melbourne and threatens its water reservoirs.

The average marked with a red line and the green one marks the trend.

Alongside the decreased rainfall, the number of completely dry days in a year has changed as well. From the plot above, you can see that the number of days when it was completely dry in Melbourne increased significantly in the 2000s. During the past few years, however, it has returned to normal. Again, marked with a green line is the trend showing that Melbourne is getting more and more completely dry days.

For more detailed examples of how you can use the Planet OS Datahub API to work with high-quality weather data, check out my Jupyter notebook on GitHub.

The Planet OS Datahub provides free access to high-quality earth science data, and is routinely updated with new datasets. If you’d like to be notified when new data becomes available, follow Planet OS on Medium or subscribe to our email newsletter to receive future updates in your inbox.