Category Archives: Australian Climate

Rainfall Shortage Sequence 03/2019

Posted in Australian Climate, Climate events, Manilla NSW, Rainfall from 1883 by

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.

March rain leaves drought extreme

Posted in Australian Climate, Climate events, Manilla NSW, Rainfall from 1883 by

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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February: Two Record Droughts

Posted in Australian Climate, Climate events, Manilla NSW, Rainfall from 1883 by

Two rainfall totals to February 2019 were the lowest ever recorded at Manilla: 271 mm in 12 months, and 3672 mm in 7 years.

Rainfall status Jan-Feb 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 February, 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 pattern

The very low rainfall of February 2019 (10.6 mm) has driven the rainfall totals lower than they were in January for nearly all the durations that are shown.
The rainfall totals up to 6 months are still not “serious” shortages (below the 10th percentile), but the only other total that is not now a serious shortage, or worse, is that for 30 years (360 months).
In recent months, extreme shortages (below the 1st percentile) have persisted at durations of 12 to 24 months, and at durations of 6 to 7 years.

Record-breaking drought

Two rainfall totals to the end of February are new drought records for Manilla.

The 12-month total of 271 mm beats 288 mm set in October 1965.
The 84-month (7-year) total of 3672 mm beats of 3699 mm set in March 1903.

Earlier, another record had been broken in September. The 15-month total of 400 mm at that date beat 404 mm set in May 1912.

Further Explanation

Drought 2018 contour chartMuch more detail was given in the post: “Contours of Manilla’s 2018 Drought” (with data up to October only). Notes include: “Long-term shortages”, “Classes of rainfall shortage”, and “Manilla rainfall records”.

One- and two-year droughts recur in January 2019

Posted in Australian Climate, Climate events, Manilla NSW, Rainfall from 1883 by

Drought contour plot to Jan 2019

This contour plot shows the progress of the extreme drought at Manilla up to January 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 January 2019, there had been six 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 with such low rainfall was September 2017.

Droughts lasting less than one year (rows 2, 3, 4, 5, 6, 9)

As the effects of low monthly rainfall added up, extreme droughts appeared (dark brown). That is, rainfall totals below the 1st percentile. (They are the lowest rainfall totals, that have occurred in less than 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 extreme shortages. By September 2018, extreme shortages extended as far as the 9-month total. That total, adding up the nine months from January to September 2018, included only one month (February) that had rainfall above normal.
In these durations of less than one year, extreme droughts were rare after September 2018. Because the last six months had no serious monthly shortages, the final month (January) includes no serious shortages for durations from 2 months up to 6 months.

Droughts of 1 year to 2 year duration (rows 12, 15, 18, 24)

By August 2018, an extreme 15-month drought appeared. That 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 all four droughts in this group (12-, 15-, 18-, and 24-month droughts) were extreme. This became true again in January 2019. By that date, some of the dry months of 2017 were no longer included, but dry months in the current summer replaced them in the total.

Related graphs

A similar contour plot with data to October 2018 is here.

A line graph of the rainfall status for January 2019 reveals that extreme shortages also exist now at the much longer durations of six years and seven years that are not included in this contour plot.

Notes

The following notes include:

Classes of rainfall shortage

Rainfall rate versus percentile rank

Limitations of this analysis

Note: Classes of rainfall shortage

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Driest 6 years since 1903

Posted in Australian Climate, Climate events, Manilla NSW, Rainfall from 1883 by

The six-year rainfall total of 3142 mm to January 2019 was the lowest in a century. The only lower totals ended in the months January, February, and March 1903.

Rainfall shortages at Dec 2018 and Jan 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 January, are shown by a black line with large circles. Those from one month earlier, at the end of December, are shown by a thinner line with smaller circles.

Changes this month

The pattern

At this date, rainfall totals for short periods, one month to six months, are below normal but they are not serious shortages (below the 10th percentile). Now, nearly all rainfall totals for nine months up to twenty years are serious shortages or worse. Extreme shortages (below the first percentile) occur at durations from 12 months to 24 months, and at 6 and 7 years. Severe shortages (below the 5th percentile) have now developed at 30 months, 36 months and 48 months.

Short-term shortages

At durations less than nine months, rainfall shortages hover around the 20th percentile. While not classed as “serious”, such values cause the drought to extend to ever longer durations.

Extreme shortages

There are now extreme shortages (1st percentile) at durations of 12 months (331 mm), 15 months (444 mm) 18 months (548 mm), and 24 months (821 mm). The extreme 7-year shortage has now worsened, to become the 7th driest on record. However, the 6-year shortage is even worse, the 4th driest.

Long-term shortages

In the longer term, serious shortages at 8 years, 10 years and 20 years persist from the December graph, and a new one appears at 15 years.
Such long-term rainfall shortages were common early in the 20th century. They have hardly occurred since the Keepit Dam was built in 1960.

Further Explanation

Drought 2018 contour chartMuch more detail was given in the post: “Contours of Manilla’s 2018 Drought” (with data up to October only). Notes include: “Long-term shortages”, “Classes of rainfall shortage”, and “Manilla rainfall records”.