21-C Climate: Mackellar cycles

At Manilla, NSW, the anomaly of daily maximum temperature has continued to track, in the opposite sense, that of monthly rainfall.

Graphical log of smoothed rainfall and temperature.

The values shown are anomalies from normal values, smoothed to suppress cycles shorter than 12 months. (See notes below on Normals and Smoothing.)

The pattern is of quasi-biennial cycles that express the insight of Dorothea Mackellar that this is a land “of droughts and flooding rains*. Hot dry times alternate with cool wet times. For temperature, I have chosen the mean daily maximum, as it best matches the rainfall.

This post updates others in the Menu Category “Manilla NSW/21st century climate/Anomalies smoothed”, such as “17 years of ‘Droughts and Flooding Rains’ at Manilla” (29/06/2014).

“Droughts” (hot dry times)

Winter-spring 2002. The drought of 2002 was extreme, having rainfall in the lowest 1% in history. Lowest rainfall anomaly was in the winter and highest temperature anomaly in the spring.

Spring 2009. The temperature anomaly in spring 2009 was as high as in 2002, but the rainfall (as smoothed) barely qualified as “drought”.

Spring-summer 2013. The maximum temperature anomaly in spring 2013 was again like that in 2002 and 2009. This time, the rainfall minimum came later, in the summer. The drought was severe but not extreme.

Autumn-winter 2018. The temperature anomaly peak was higher than the earlier peaks. The minimum rainfall anomaly that followed in the winter was again extreme.

Summer 2018-19. At this time, the temperature anomaly was the highest, and the rainfall anomaly the lowest on this graph.

“Flooding Rains” (cool wet times)

Spring 2005. The spring of 2005 was wet, but the temperature was not cool but rather warm.

Summer 2007-8. Although the summer of 2007-8 was cool, rainfall was normal. Continue reading

Cycling into drought

Graph of rainfall versus temperature at Manilla

In the last three years, the climate of Manilla has moved into drought. Rainfall has become lower than normal, and days have become warmer than normal.

The pattern of change

The pattern of change is clear on this graph only because the rainfall and temperature anomalies have been smoothed. Values for the last six months cannot yet be smoothed so well. Their pattern is ragged.
The first point on the graph, July 2015, is close to the Zero-Zero point of normal climate, marked by a circle in turquoise. Since then, the climate has cycled mainly along the blue line joining the two corners marked “Hot Dry ‘Droughts'” and “Cold Wet ‘Flooding Rains'”, as in Dorothea Mackellar’s poem “My Country”.
For the first seven months, to February 2016, while rainfall hardly changed, the temperature rose to above normal. Then, by August 2016, the climate became unusually cold and wet. This first cycle ended in January 2017 at the hot-dry limit of normal climate.
From February 2017, a second cycle began with movement towards cool and wet, but that ceased in May without getting as far as normal. Since May 2017, the movement has been persistently towards hot and dry.
The final smoothed data point, December 2017, is close to the 21st Century record for both low rainfall anomaly (minus 27.1 mm/month in July 2002) and high daily maximum temperature anomaly (plus 1.39 degrees in October 2013). New records seem likely to be set when values for 2018 can be smoothed.

Length of cycles

The cycles on this graph have a period close to one year. February had the highest smoothed daily maximum temperature anomaly in 2016 and in 2017. When smoothed, the same may be true in 2018.
Historically, the cycles cold-wet to hot-dry have a period of about two years (“quasi-biennial”) at Manilla and in Australia as a whole.
The climate cycles or climate trends associated with Global Warming have periods that are very much longer. They do not show on this graph. If they did, they would show as movement on the other diagonal, between the corners marked “Cold Dry ‘Glacial'” and “Hot Wet ‘Interglacial'”.

The 2002 drought

The most recent extreme drought was in 2002. A similar graph for that drought is in the post “Profile of an Extreme Drought”.

For context, see the post “Manilla’s Record of Droughts”.

Graphs of other variables

The graph in this post is one of a set of six, showing smoothed anomalies of variables versus smoothed daily maximum temperature. The variables are: rainfall, cloudiness, dew point, daily temperature range, daily minimum temperature, and subsoil temperature.
All six graphs, with further explanation, are in another post.