October: 20-year extreme shortage

Rainfall status Manilla Sep-Oct 2019

Most rainfall shortages are now extreme

The Rainfall Status graph for October 2019 at Manilla shows extreme rainfall shortages (below the 1st percentile) at most durations.
Of the 25 durations shown, 16 are now extreme shortages, and 7 are severe shortages (below the 5th percentile).
That leaves only 2 that are not far below normal: the October 1-month rainfall (21.4 mm) at the 16th percentile, and the 360-month (30-year) total (18696 mm) at the 14th percentile. Even this 30-year total is lower than any seen here since 1952.

A long-duration extreme shortage

An extreme shortage has now appeared at the very long duration of 240 months (20 years). In the 20 years since November 1999 the total rainfall was only 11893 mm – the 6th driest in history. Drier 20-year periods occurred only in the 1940’s and 1950’s.
Given that the median 20-year rainfall at Manilla is 13010 mm, this is a shortfall of 1117 mm, which is nearly two years of rainfall lost.

Only three new records this month

In this drought, rainfall totals in the 1- to 7-year range have broken records for low rainfall repeatedly. This month only three records have been broken: 24-months (615 mm), 30 months (850 mm), and 36-months (1111 mm).

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

More drought records in September 2019

Rainfall status Aug-Sep 2019 Manilla

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 September, 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.]

Record low rainfalls for 15-months to 36-months

With only 1.2 mm of rain falling in September 2019, most of the rainfall totals that had been record low values in August fell further to become new records. Some of these rainfall totals had been getting lower in each of the last four months. Until 2019, these records for low rainfall had not been broken in half a century, some having been set in the great drought of 1966.
Some of the current rainfall totals are very much lower than the previous long-standing records. For example:

  • 18-month total to Sep 2019: 384 mm; to Apr 1966: 514 mm; now lower by 130 mm.
  • 30-month total to Sep 2019: 853 mm; to Oct 1966: 1078 mm; now lower by 225 mm.
  • 36-month total to Sep 2019: 1161 mm; to Jan 1947: 1333 mm; lower by 172 mm.

Record low rainfalls for 72-months and 84-months

Record low rainfalls for 72-months and 84-months, which had appeared during 2019, got steadily lower. The earlier records had stood for more than a century, (Feb, Mar 1903) but are now beaten by about 100 mm.

The latest four months

September’s low rainfall has dragged down the totals for 2-, 3-, and 4-months. The 4-month total of 22 mm is the 2nd lowest ever.

The pattern of this drought

Two features of this drought are now clear from this data:

  • It is an extreme drought of two to three-year duration: one of Manilla’s six great droughts.
  • Record-breaking rainfall shortages at 72-month and 84-month duration show that the summer droughts of 2012-13 and 2013-14 still have an effect, not compensated by the wet winter of 2016.

Table of lowest-ever rainfalls

In a post of July 2018, I tabulated the lowest-ever rainfall for selected durations up to 360 months.

I commented that such records are rarely broken, and all had stood for at least forty-six years at that date.
The current drought has now broken most of those records for durations between 12-months and 84-months


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

New drought records in August 2019

Rainfall status July-August 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 August, 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.]

Record low rainfall values

August rainfall of only 5.6 mm at Manilla has brought more drought records. The rainfall totals for 18-, 24-, 36-, 72-, and 84-months are new record lows.
The record-low 36-month total is remarkable. Only the great droughts of 1947, 1914, and 1967 had rainfall nearly so low for so long, but the current 36-month total (1283 mm) is more than 50 mm lower than in those great droughts. Given that Manilla’s mean  annual rainfall is 652 mm, 1283 mm represents less than two years of rainfall in three years.

Severe and extreme rainfall shortages

For plotted durations longer than four months, only the very longest (30 years) is not a severe or extreme rainfall shortage. For durations beyond 84 months (including 30 years) every total is lower than has been seen since 1954, 65 years ago.


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

Drought worse in July.

At Manilla, most rainfall totals just got lower.
Rainfall status June and July 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 July, 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.]

Results for July

Rainfall totals for months to July 2019 are the lowest ever registered here for six of the twenty-five chosen rainfall durations: 15-, 18-, 24-, 30-, 72- and 84-months.
Only three of the chosen durations do not have serious rainfall shortages below the 10th percentile: 1-month, 3-months and 360-months. Even those three values are far below normal, at the 12th, 14th, and 14th percentiles.

Weatherzone forum closed

I posted a provisional version of this graph to catch the final deadline for posting to the weatherzone forum. My first post was nearly 16 years ago.
That forum is now closed to postings and will close completely in November. It closed due to lack of public interest in climate and weather in Australia.


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

June breaks more drought records

Rainfall status May-June 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 June, 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.]

Changes from May to June

The June rainfall of only 4.8 mm took Manilla’s rainfall status curve back to where it was in April.
Five records for low rainfall totals have been broken yet again: the totals for 15-, 18-, 24-, 30-and 72-months. The 84-month total at June (3660 mm) is also extremely low, but ranks second-driest to April 2019.
The record for a 15-month dry spell, which had stood at 404 mm since 1912, has been broken four times in this drought, and now stands at 367 mm. That is down by 37 mm, or nearly 10% below the 1912 figure. The 24-month record had stood at 766 mm since 1966 when it was broken this April, May, and June. It now stands 73 mm lower, at 693 mm.


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

May 2019 rain gives some relief

Rainfall status Apr-May 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 May, 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.]

Changes from April to May

Above-average rainfall in May relieved the drought situation in some ways. Rainfall shortages of 3-, 4-, 5-, and 6-month duration are no longer serious. The 9-month shortage is reduced from severe to serious, and the 12-month shortage from extreme to severe.

May rain did not prevent the rainfall total for 15 months falling to the record low value of 388 mm. The record, which had been set at 404 mm in 1912, has been broken three times in this drought: to 400 mm in September, 397 mm in April, and 388 mm in May.

Nearly all rainfall shortages at long and very long durations have been reduced to some extent. However, extreme shortages persist not only at 15-months, but also at 18-, 24-, 30-, 72- and 84-months.


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

April 2019: 7 lowest rainfall totals

In April 2019, rainfall totals were the lowest-ever values for 1 month and for 15, 18, 24, 30, 72, and 84 months.

Rainfall status Mar-Apr 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 April, 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.]

Record and near-record low rainfall totals

There never has been a month at Manilla when rainfall totals have included so many record or near-record low values.

  • The 1-month total for April is zero (as in April 1912, 1925, 1942, and 1971).
  • The 12-month total of 283 mm is second-lowest after February 2019 (271 mm).
  • The 15-month total of 397 mm is a new record, beating September 2018 (400 mm).
  • The 18-month total of 510 mm is a new record, beating April 1966 (514 mm).
  • The 24-month total of 745 mm is a new record, beating July 1966 (766 mm).
  • The 30-month total of 1005 mm is a new record, beating March 2019 (1078 mm).
  • The 72-month total of 3060 mm is equal-lowest with February 1903.
  • The 84-month total of 3653 mm is a new record, beating February 2019 (3672 mm).

Other changes from March to April

When rainfall in April was 55 mm less than in March, the short-duration totals for 3, 4, 5, and 6 months became serious shortages again.
New severe rainfall shortages appeared at the very long durations of 144 months (12 years) and 240 months (20 years). Such shortages have not been seen in half a century: not since 1969 in the case of 144 months duration, and not since 1950 in the case of 240 months duration.

May and June 2019 data

Data for the following month, May 2019, is plotted in the same way in the post “May 2019 rain gives some relief“. See also “June breaks more drought records”.


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