Hot and dry records in January 2019

In January 2019, the smoothed anomaly value of monthly rainfall reached a record low (-31.8 mm/month), and that of monthly mean maximum temperature a record high (+1.79°).

Rainfall and temperature trajectory Sep2016 toFeb 2019

[This graph is extracted from a forthcoming post in the series “3-year trends…”. ]

This graph shows temperature and rainfall anomalies, not raw data. It shows how far the actual values differ from normal. The 30 data points from September 2016 to February 2019 (coloured red) are smoothed to show only cycles longer than one year.

The earliest data point, September 2016, had temperature and rainfall just beyond the normal range on the cool and wet side (lower left). Since that date, all the smoothed data points have fallen close to the sloping Mackellar trend line (blue) from cool-wet to hot-dry. (See the note below: Mackellar trend line.)
In the 4 months up to January 2017, warming and drying was rapid, passing completely through the “normal” range. Next, some cooling and wetting occurred to May 2017, then warming and drying resumed to a full drought in March 2018. Through the year 2018, drought prevailed, with a rainfall anomaly always below -25 mm. The temperature anomaly fell to only +1 deg by August, but rose again while rainfall fell. Records for low rainfall and high temperature were broken repeatedly.
January 2019 had the lowest smoothed monthly rainfall anomaly of the 21st century (-31.8 mm/month), and the highest monthly mean maximum temperature (+1.79°).
The following month, February 2019, had a slightly decreased temperature anomaly, and an increased rainfall anomaly. Later data points with less smoothing applied suggest that the smoothed record values of January may stand for some time.


Mackellar trend line

The insight of Dorothea Mackellar that this is a land “of droughts and flooding rains” *
is expressed in these graphs by a blue trend line passing through the “Normal” point in the centre (aqua) and extending both to “Droughts” with high temperature and low rainfall at the top right and to “Flooding Rains” with low temperature and high rainfall at the bottom left. Smoothed data points for anomalies of mean monthly daily maximum temperature and monthly rainfall totals generally lie close to the sloping blue line in such graphs for all of the last 20 years. (Search “3-year climate trends”, this one, for example).

Notice that record high and low values of smoothed anomalies of rainfall and daily maximum temperature (dates marked in blue) lie close the this blue line, supporting the estimate.
Empirically, one degree of increase in temperature anomaly matches 20 mm of decrease in monthly rainfall anomaly: the Mackellar Constant for Manilla is -20mm/month/degree.

* By arrangement with the Licensor, The Dorothea Mackellar Estate, c/- Curtis Brown (Aust) Pty Ltd.