December 2019: 10 new drought records

Rainfall status Nov-Dec 2019

Changing shortages

December rainfall of 19.6 mm, added to November rainfall of 40.2 mm, reduced the shortages for durations up to six months, but it did not prevent the drought becoming worse at nearly all longer durations. The shortage was extreme (1st percentile) at every duration beyond 6-months, except at 120-, and 144-months (severe shortage) and at 360-months (serious shortage).Although the 360-month total of 18,596 mm, being at the 10th percentile, is merely a “serious” shortage, this is the lowest 360-month rainfall total since 1952!

Record low rainfalls

New record low rainfall totals were set in December 2019 as follows:

12-months duration: 255 mm;
24-months duration: 582 mm;
30-months duration: 791 mm;
36-months duration: 1099 mm;
42-months duration: 1477 mm;
48-months duration: 1833 mm;
60-months duration: 2455 mm;
72-months duration: 2901 mm;
84-months duration: 3477 mm;
96-months duration: 4146 mm.

For most of these durations, the record had already been broken several times in this drought. However, three of these records had stood for over a century:

42-month duration: 1477 mm beats (by 43 mm) the record of 1520 mm set in September 1914;
48-month duration: 1833 mm beats (by 3 mm) the record of 1836 mm set in February 1915;
60-month duration: 2455 mm beats (by 11 mm) the record of 2466 mm set in February 1916.

How to read the graph

This graph shows all the present rainfall shortages at Manilla, short term and long term, as percentile values. The latest values, as at the end of November 2019, are shown by a thick black line with large circles. Those from one month earlier are shown by a thinner line with small diamonds. [The method is described in “Further Explanation” below.]


Further Explanation

The following notes explain aspects of this work under these listed headings:

Data analysis

Cumulative rainfall totals
Percentile values
Severity of rainfall shortages

Limitations of this analysis

Monthly rainfalls form a single population
Observations are not retrospective
The rain gauge failed

Data analysis

Continue reading

December 2019: very hot and dry

Sun in smoke

Red Sun 17 Dec

After the first week, each week in December was very hot, reading up to 5.9° above normal. Both days and nights were hot, but only one record was set: 42.2° on the 21st was the hottest December day. That was well below the record hot day of 44.9° set on 11/2/17.
Twenty mornings were cloudless which was twice the usual number. Smoke from mainly coastal bushfires reduced visibility to 15 km or less from the 8th to the 25th. Early in the month, rain fell on three days, the highest reading being 12.4 mm on the first day.

December 2019 weather

Comparing December months

This month broke 21st century records for December mean monthly temperatures. The mean minimum of 18.7° just beat 18.6° of December 2009, the mean average of 27.6° easily beat 26.1° last year, while the mean maximum of 36.5° was far above last year’s 33.9°.
On balance, indicators of moisture make this the driest December of the century. Rainfall, at 19.6 mm, was lower than any but December 2006 (18.8 mm), and the dew point was equal lowest with 2013. This month had by far the fewest cloudy mornings (10%) and the widest daily temperature range (17.8°).

December 2019 climate

Drought

I will report separately on the on-going drought that continues to break low-rainfall records at durations of 15-months and longer.


Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available. Recording resumed on 20 July 2019.
My estimates of early morning dew point have drifted anomalously low. From August 2019, I use data from the Tamworth Airport published graphs.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to December 2019

December dry and very hot

3-year trends of climate anomalies

December raw anomaly data (orange)

Temperatures

Daily maximum temperature anomaly (all x-axes) extremely high: now five degrees above 21st century normal and three degrees above the record for smoothed values.
Daily minimum temperature anomaly (lower left): very high, just above the record smoothed value.
Subsoil temperature anomaly (lower right): still near normal.

Moistures (moist is at the bottom)

Rainfall anomaly (upper left): extremely low.
Cloudiness anomaly (upper right): extremely low.
Dew point anomaly (middle left): still rather low.
Daily temperature range anomaly (middle right): very high.

 Fully smoothed data values (red) 

Smoothed anomaly values now include June of 2019. From the rather static values of the spring, nearly all smoothed values for June began to move in the direction towards drought that seems to have prevailed since then.
There were two exceptions. Daily minimum temperature anomaly continued to fall very rapidly. Subsoil temperature anomaly approached a peak value.

Detail of rainfall vs. max temp

Rainfall and temperature anomaly trendsThe relation of smoothed rainfall anomaly to smoothed daily maximum temperature anomaly (top left graph) is important, but the graph is hard to read. I have drawn a part at a larger scale here.
The value for September 2017 is the first to show the current drought by falling on the hot-dry side of the normal range (aqua). Values became successively warmer and drier until March 2018 (max temp) and May 2018 (min rain). Values (especially temperature) then cycled away from drought until August-September 2018, and back to record-breaking drought in January 2019.
After January 2019, there was a retreat from drought until May 2019, when anomaly values were like those of 17 months earlier, in January 2018 (red square).
June 2019 began a renewed cycle towards drought, seemingly confirmed by later data.


Notes:

January data points are marked by squares.

Smoothing Continue reading

Rainfalls: 8 in the 0.1th percentile

Rainfall status October November 2019

Normal rainfall in November

Rainfall in November 2019 (40.2 mm) was near normal. That reduced shortages at durations from 2-months to 5-months. Otherwise it had little effect: fifteen of twenty longer durations remained extreme shortages.

Values plotted in the 0.1th percentile

For simplicity, the bottom line is labelled with the 0.1th percentile value, and percentile values below 0.1% are plotted on the line. As there are 1600 months of record, both the 2nd-driest month (percentile value 0.063%) and the driest month, (percentile value 0.000%, by convention), which would plot below the line, are plotted on it.
Driest records have again been broken at durations of 12-months (270 mm), 24-months (611 mm), 30-months (834 mm), 72-months (2927 mm), and 96-months (4205 mm). The 96-month record had stood at 4405 mm since November 1919.
A value that equals an earlier record occurs at 84-months (3555 mm).
Values that are 2nd-driest occur at 36-months (1129 mm) and at 240-months (11816 mm). The 240-month (20-year) total is now only 50 mm more than the lowest-ever value of 11766 mm set in February 1931.

How to read the graph

This graph shows all the present rainfall shortages at Manilla, short term and long term, as percentile values. The latest values, as at the end of October 2019, are shown by a thick black line with large circles. Those from one month earlier are shown by a thinner line with small diamonds. [The method is described in “Further Explanation” below.]


Further Explanation

The following notes explain aspects of this work under these listed headings:

Data analysis

Cumulative rainfall totals
Percentile values
Severity of rainfall shortages

Limitations of this analysis

Monthly rainfalls form a single population
Observations are not retrospective
The rain gauge failed

Data analysis

Continue reading

November 2019: one warm week

Bushfire smoke

Manilla View 18-11-2019

One week, beginning on the 20th, was 5.4° warmer than normal. The night of the 22nd did not get cooler than 24.0°, making it the 5th warmest November night in this century. (One night in November 2009 had been 27.8°, the warmest night of any month.) In other weeks of this month, temperatures were normal.
Most days were dry and sunny. However, days early and late in the month were cloudy, with high dew points and narrow daily temperature ranges. Six of these days had rain, with the highest reading 16.4 mm on the 4th.
Smoke from coastal bushfires reduced visibility from the 17th to the 29th. On the 18th, visibility was only one kilometre, as shown in the photo.

November 2019 weather log

Comparing November months

Although this month was warm. other November months have been warmer: in 2002, 2009, 2012, and 2014. All of these had especially warm days. While days this month averaged 31.8°, days in November 2009 averaged 34.3°. The coolest recent November was in 2017.
This was a dry month but, by various measures, not as dry as in 2002, 2009, 2014 or 2016. The rainfall total of 40.2 mm is in the 27th percentile.

November climate

Drought

I will report separately on the on-going drought that continues to break low-rainfall records at durations of 15-months and longer.


Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available. Recording resumed on 20 July 2019.
My estimates of early morning dew point have drifted anomalously low. From August 2019, I use data from the Tamworth Airport published graphs.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to November 2019

November just like October

3-year trends to November 2019

November raw anomaly data (orange)

Temperatures

Daily maximum temperature anomaly (all x-axes): now three degrees above normal.
Daily minimum temperature anomaly (lower left): remains high.
Subsoil temperature anomaly (lower right): still near normal.

Moistures (moist is at the bottom)

Rainfall anomaly (upper left): still very low.
Cloudiness anomaly (upper right): still normal.
Dew point anomaly (middle left): still rather low.
Daily temperature range anomaly (middle right): has risen back to high.

 Latest fully smoothed data (red) includes autumn 2019

Smoothed anomaly values are now available for the autumn (MAM) of 2019. Generally they show a steady retreat from the extreme (smoothed) anomaly values of January. Rainfall anomaly rose, while daily maximum temperature anomaly fell. Daily minimum temperature anomaly fell rapidly, and subsoil temperature anomaly rose rapidly. Cloudiness and dew point changed little. Temperature range anomaly, which had decreased slowly to January, began to increase again.


Notes:

January data points are marked by squares.

Smoothing Continue reading

How much rainfall is now lost?

Rainfall deficits in mm at Manilla NSW, Oct 2019

This graph shows the total rainfall shortage in this drought at Manilla NSW. It uses the same rainfall figures as in the October Rainfall Status graph, that is, the rainfall totals for up to 360 months. In this case, I have subtracted from them the normal rainfall totals. That shows the rainfall deficit: how much less rainfall we have had than we normally would.

Generally a 1-year deficit

In many cases, the shortage now is about 650 mm, or one year of normal rainfall. This is true when calculated for 24-months and for several other durations including 360-months. In broad terms, this drought has left Manilla about one year short of rain.

Deficits are smaller at short durations.

A one-year deficit could occur at a duration of 12-months only if there were no rain. A curve on the graph shows “No rain at all”. A second curve is labelled “50% of normal Rain”. These October data show that the rainfall totals for durations below 24-months are around 30% of normal.

Deficits larger than 650 mm occur at some long durations

There are three dips in the curve where deficits are greater than one year of rainfall.

  1. The 3-year deficit is now 820 mm, due to very low rainfall in the last six months. Such values may yet appear at other durations.
  2. The 7-year deficit is now 920 mm. This deficit is due to the inclusion of severe rainfall shortages of 12-month to 30-month duration in 2013 and 2014. These appear on this drought duration graph, but were scarcely noticed at the time.
  3. The 20-year deficit is now 1100 mm. The 650 mm deficit due to the current drought is supplemented by deficits of some 200 mm carried forward from both the 2013-14 shortages (above) and the extreme 12-month shortage of 2002.

What the deficits mean

In times of normal or excess rainfall, the whole terrain is kept supplied with water. It goes to aquifers deep underground, to shallow aquifers near streams, to stream-flow, and to the soil and plants. In general, the longer the duration of normal or excess rainfall, the larger the reservoirs, both underground and on the surface, that can be filled.
The present deficit of one year of rainfall must have drawn down all the reserves of water in the terrain. The empty state of the Keepit Dam (0.8%) is an obvious result, but all other reserves must have fallen.