Rainfall Shortage Jan 2000 – Mar 2019

Severe and extreme rainfall shortages Jan 2000 to Mar 2019

The current drought now has an extreme rainfall shortage of 84 months duration that must have commenced in 2012.

A new graph

This graph shows the onset, persistence, and breaking of episodes of extreme and severe rainfall shortage (droughts) at Manilla since 2000. It is a part of a graph of the complete historical record from 1884. In this case, the time axis is expanded to resolve individual months. The graph features and the data analysis are explained in the post “Rainfall Shortage History: Manilla”.

Extreme shortages, up to the 1st percentile, are shown in red and severe shortages, up to the 5th percentile, are shown in grey.
The dashed line labelled “Last Good Data” is a limitation to determining cumulative rainfall deficiency. Future observations may make any point to the right of this line more extreme.

The pattern of rainfall shortages

Shortages before 2018

In 2000 there were no rainfall shortages classed as “severe”. There had been hardly any since 1994.
The drought that occurred in winter 2002 had extreme rainfall shortages at all durations from 3 months to 12 months. Severe shortages extended even further: from 2 months to 30 months. However this was a much shorter drought than six others in the history of Manilla.

Although severe rainfall shortages (grey) occurred at intervals between 2002 and 2018, they formed small clusters, mainly at short durations. Years affected were 2005, 2008, 2009, 2012, 2013, 2014, and 2017. By 2014, there was public concern about shortage of rainfall. Although there were few seasonal severe shortages at that time, the graph shows that there were severe shortages at durations from 12 months to 30 months through 2013 and 2014.

With the benefit of current data, we can see that severe and even extreme shortages of duration longer than 60 months were, in fact, initiated in 2012 or earlier. They were not apparent at the time, however. In October 2016, in a post “Is There Any Drought Now?”, I argued that there was no evidence of drought at that time.

An alternative expression of rainfall status during this time is a graph of smoothed rainfall anomalies in the post “17 Years of “Droughts and Flooding Rains” at Manilla”.

Shortages at 2018

Shortages of rainfall became alarming in 2018. The winter months had extreme shortages of 2-month to 6-month duration. Earlier and later dry months contributed to a 15-month extreme shortage, such as had not occurred since 1966, half a century earlier.
After November 2018 none of the short-term rainfall totals for durations less than nine months has been even a severe shortage. In other respects, the drought has deepened. As recent monthly rainfall values have scarcely risen above normal, durations of severe or extreme shortage have become longer and longer. As at March 2019, extreme shortages prevail at 30 months, 72 months and 84 months. Severe shortages prevail at even longer durations, now up to 120 months (10 years).


Notes

The Millennium Drought absent
“Rainfall Shortages” or “Droughts”?
Short droughts are worst

The Millennium Drought absent

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Rainfall Shortage History: Manilla

Complete record of droughts, Manilla NSW

Manilla had great droughts in 1902, 1912, 1940, 1946, 1966, and 2018.

A new graph

This new graph records all historic periods of severe and extreme rainfall shortage at Manilla NSW. Data show 25 values of duration from 2 months to 360 months. Unlike the graphs of rainfall shortage in earlier posts, this graph shows the months of onset, persistence, and breaking of each occurrence. [See the Note below: “An innovative graph”.]
Extreme shortages (up to the 1st percentile) are shown in red and severe shortages (up to the 5th percentile) are shown in grey.
The dashed lines labelled “First Good Data” and “Last Good Data” are limitations that apply to all cumulative rainfall deficiency data. [See the note below: “First Good Data; Last Good Data”.]

“Rainfall Shortages” or “Droughts”?

Although droughts involve other factors, rainfall shortage is decisive. Some other factors, such as daily maximum temperature anomaly, vary in the same sense, Australia-wide.
Recognised times of drought at Manilla appear on this graph as extended periods of severe or extreme rainfall shortage .
To simplify, I have separated the graph into three parts according to the duration of the shortages: seasonal droughts, great droughts, and decadal droughts.

Complete record of seasonal droughts

Seasonal droughts.

Droughts with extreme shortages of rainfall that lasted up to nine months happened often. Counting those with more than one red marker, there were 16 seasonal droughts in 136 years: about one in each nine years. Gaps as short as four years happened around 1920, while the longest gap of 16 years came between 2002 and 2018.
The most common season of extreme rainfall shortage was winter, with 8 cases. Autumn had 5 cases and spring 3 cases, while summer had none.
Some of these seasonal droughts became Great Droughts.

Complete record of the great droughts

The Six Great Droughts: 1-year to 9-year duration.

According to this graph, Manilla has suffered six great droughts, attested by extreme shortages of rainfall at more than 2 of the 13 chosen duration values from 12 months to 108 months. They were:

(1.) 1902 (the Federation Drought);
(2.) 1912;
(3.) 1940 (first part of the World War II Drought);
(4.) 1946 (second part of the World War II Drought);
(5.) 1966;
(6.) 2018.

[The absence of the Millennium Drought is discussed in the Note below.]

BoM continental rainfall maps

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Rainfall Shortage Sequence 03/2019

Sequence of raiinfall shortages to March 2019

By March 2019, extreme shortages of rainfall occur at durations from 12 months to 30 months.

This contour plot shows the progress of the drought at Manilla up to March 2019. Colours show rainfall shortages as percentiles. Dates plot along the top, and durations down the side.

One month rainfall totals (on the top row)

By March 2019, there had been eight months without serious monthly rainfall shortages. The months of serious rainfall shortage (light brown) were earlier, in May, June and July 2018. The only other month in the last two years with such low rainfall was September 2017.

Shortages lasting less than one year (rows 2 to 9)

As the effects of low monthly rainfall added up, extreme shortages appeared (dark brown). That is, rainfall totals in the lowest 1% of the historical record.
By June 2018, the 2-month and 3-month totals were already extreme shortages. Similarly, by July, the 3-month, 4-month, and 5-month totals were all extreme shortages. By September 2018, extreme shortages extended as far as 9-month totals. That total, adding up the nine months from January to September 2018, included only one month (February) that had rainfall above normal.
In these shorter durations, extreme shortages were rare after September 2018. The final month plotted (March) includes no shortages (not even “serious” ones) for durations from 2 months up to 6 months.

Shortages of 1-year to 3-year duration (rows 12 to 36)

By August 2018, an extreme 15-month shortage appeared. The 15-month total then included not only the dry months of winter 2018, but also the dry month of September 2017. By September 2018, the 15-month total became the driest on record (400 mm). By October four totals in this group (12-, 15-, 18-, and 24-month totals) were extreme shortages. That was true again in January 2019. By that time, some dry months in 2017 were excluded, but dry months in the 2018-19 summer were included.
In February 2019, as the four extreme shortages of the previous month persisted, the 12-month total became the driest on record (271 mm). March also had four extreme shortages in this group, but now they were at 12, 15, 24 and 30 months. The 24-month total (769 mm) was the second-driest on record and the 30-month total (1078 mm) equal driest.

A related graph

A line graph of the rainfall status for March 2019  extends to durations much longer than the 36 months shown in this contour graph. It reveals that extreme shortages exist at durations of six years and seven years.


Data and method

This kind of graph simply displays the time sequence, month by month, of rainfall shortages that I have displayed on line graphs prepared for each month. In the post for the most recent line graph (March 2019) I have described my method of analysis and its limitations.

Very warm nights in March 2019

Photo of dead public lawn

Our Nature Strip

While there were no very high or low temperatures, weekly mean temperatures were high. Warm spells through the second and fourth week-ends were about four degrees high.
There were nine rain days (twice the usual number for March), but none had more than 5 mm until the 30th. A rain front early that morning brought 39 mm.

Weather log for March 2019

Comparing March months

This month was very warm. It was like March in 2018 and 2016, but the nights were warmer. Both the mean minimum temperature (17.9°) and the monthly mean temperature (24.9°) were record high values for March in the 21st century.
It was not a dry month: values of all the moisture indicators were near normal. The (estimated) rainfall of 54.9 mm is very close to the long-term average of 53.4 mm. However, March rainfall at Manilla is strongly skewed, having many values just below the average and just a few values up to 240 mm above it. The median March rainfall is much lower: only 39 mm. This month’s total of 54.9 mm is at the 60th percentile: it is higher than 60% of all historic March rainfall values.
I have reported the on-going drought in another post.

The last 7 March months


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.  Since no 9 am readings have been recorded since August, I have substituted my non-standard gauge readings for all days.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to March 2019

March warm

3-year trends to March 2019

March raw anomaly data (orange)

In March 2019, the raw anomaly for daily maximum temperature was near the upper limit for normal. Daily minimum and subsoil temperatures were high. Rainfall and other moisture measures were near normal.

 Fully smoothed data (red)

Fully smoothed data to September 2018 (except daily minimum temperature anomaly) showed a movement away from drought. More recent data, only partially smoothed, suggest that temperatures and rainfall later returned towards drought.


Notes:

January data points are marked by squares.

Smoothing

Smoothing uses Gaussian functions.
For fully smoothed data the function has a Standard Deviation of 2.5 months, it spans 13 monthly data points, and has a half-width of 6 months, which suppresses cycles shorter than 12 months. For partly smoothed data, the span of the function is reduced to 11 months, 9 months and so on.
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March rain leaves drought extreme

Above-average rainfall in March reduced the shortage of rainfall in the last 3 months. It did not relieve extreme shortages at durations between 12 months and 7 years.

Rainfall status Feb-Mar 2019

Graph of Rainfall Shortages

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 March, are shown by a thick black line with large circles. Those from one month earlier are shown by a thinner line with smaller circles. [The method is described in “Further Explanation” below.]

Good rain in March

A rain front at the end of March 2019 that brought about 40 mm took the March total up to the average. This raised the 2-month and 3-month totals nearer to normal. It did nothing to increase longer-duration totals.

Extreme rainfall shortages

By February, six of the eleven rainfall shortages measured over durations from 12 months to 7 years were extreme. (That is, those totals were in the driest one percent in history.)
Despite the high rainfall of March, March figures also record six extreme shortages. The 18-month total is no longer extreme, but the 30-month total has now become extreme.
Two of the rainfall totals (plotted on the 0.1% line) are near-record low values. The 24-month total of 769 mm is the second lowest after July 1966 (766 mm). The 30-month total of 1078 mm is equal lowest with October 1966.
Data for February, plotted on the thinner line, show the record low values for 12 months (271 mm) and for 84 months (3672 mm).

The previous 24 months

The development of this drought through the previous 24 months is shown in the later post “Rainfall Shortage Sequence 03/2019”. A contour graph shows severity of shortage by contoured layer tints, with serial months on the x-axis and duration of shortage on the y-axis.


Further Explanation

[Update 5 April 2019.]

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

This graph is based on analysis of monthly rainfall totals from 1884. Using the spreadsheet application Excel, I calculate cumulative totals and their percentile values. Using these values, I identify rainfall shortages as serious, severe, or extreme .

Cumulative rainfall totals

I prepare two tables. The rows in each table are serial months, more than 1600 in total. The columns in each table are headed by the selected number of months, n, as specified below. In the first table I cumulate the rainfall totals. First, I add each month’s rainfall total to that of the previous month for a 2-month total. Using the previous two months, I get a 3-month total, and so on. In this way, I get n-month rainfall totals from n = 1 up to n = 360 (30 years). However, I calculate for only the following 25 values of n:

n = 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 24, 30, 36, 42, 48, 60, 72, 84, 96, 108, 120, 144, 180, 240, 360

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2018-19 summer 2nd driest

Cumulonimbus and towering cumulus

Storm at Dusk

This summer had 7 very hot days above 40°, and 11 very hot nights above 24°.
The worst heat waves came in January. Around the 17th, weekly temperatures were more than 6° above normal, with days at about 41°, and nights 24°. Near the 28th, nights were even warmer. Episodes of very low dew point came at times of lower temperature.
Thirteen rain days were scattered through the season, the highest readings being 25.0 mm on 16 December and 18.0 mm on 21 January.

Weather log summer 2018-19

Comparing summer seasons

Average temperatures were almost the same as in the hot summer of 2016-17. Days, at 35.5°, were slightly cooler and nights, at 20.1°, slightly warmer. The resulting average, 27.8°, was a new record summer temperature, beating 2016-17 by 0.2°.
Remarkably, the mean subsoil temperature, 25.5°, was not high, but normal.
Similarly, daily temperature range (15.4°) and cloudiness (22%) were normal. (Recent summers have been cloudy.) Dryness was shown only by very low humidity and rainfall.
The mean early morning dew point for this summer (10.4°) was second lowest in the 19-year record. Only that of summer 2013-14 (8.6°) was lower.
The total rainfall for the summer, 70 mm, was equal second driest with 1965, the driest summer being 1930, which had 66 mm.

Climate for summer 2018-19


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. Station 55312 recorded no readings this summer. I used my own readings for the whole season.

All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.