Tag Archives: extreme droughts

Is There Any Drought Now?

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

No. In Manilla just now, there is no drought of any kind: not a short drought, a medium-length drought, or a long drought; not an extreme drought, a severe drought, or even just a serious drought.

A new comprehensive graph of the severity of drought at one site.

In this graph, each line of data points is for one particular month. The middle line, joining the red squares, shows the whole rainfall drought situation for last month: September 2016.
This is a new kind of graph. (See Note 1 below.) It can show how severe a drought is, not only during the last month or two, but during the last year, and during the last many years. That is a lot of information.

How to read the graph

A month of extreme drought would have data points very low down on the graph. The scale on the left side is amount of rainfall. It must be a “percentile” value. For example: if the amount of rain that fell is just more than has been seen in the driest 5% of all months, it has a value in the 5th percentile. (See Note 2 below.)

Along the top and bottom of the graph I have plotted a number of months.
The number does not show time passing. It shows the number of months I included in a calculation. For each month on record I did many calculations. I added up the total rainfall for:
* the month itself;
* two months including the previous month;
* three months including the month before that;
* … and so on.
I found the totals for larger groups of months extending back as far as 360 months (30 years).
Using all these rainfall totals, I calculated percentile values to plot on the graph. For example, for groups of 12 months, all groups of 12 consecutive months are compared with each other, to find the percentile value of the 12-month period ending in a given month. (See Note 3 below.)

Which months had the most drought and least drought?

The worst drought there could ever have been would be one with data points along the bottom line of the graph. In such a disastrous month, all the rainfall totals would be the lowest on record, not just the one-month total, but also the two-month total and so on up to the 360-month total. Every one of them would be the lowest total on record. It has never been as bad as that.
The “best” time, in terms of being free of drought, would be a month with all its data points along the top edge of the graph. For that month, every rainfall total, for a short period or a long period, would be the wettest on record.
From the Manilla rainfall record, I have chosen to display the most drought and the least drought that actually occurred.

The most drought: August 1946

The month of August 1946 had no rain. Of course, that was the lowest rainfall for any August month (One among 13 months on record that had no rain.). As a result, the percentile rank for that month’s rainfall is zero. Most totals for groups of any number of months ending in August 1946 are also on the “zero-th” percentile, that is, the lowest on record. Thus, it was an extreme drought in the short term, medium term and long term.
For this month, percentile values that are above the third percentile occur in the totals for 48, 60, and 72 months, as shown. These figures, while not extremely low, were still well below normal (Normal is the 50th percentile.). They occur because these totals include some wet months in 1940, 1941, and 1942.

The least drought: March 1894

March 1894, with 295 mm of rain, was one of the the wettest months ever, ensuring a 100th percentile value. The rainfall totals for groups of months ending in that month included six other “wettest ever” values, and all other groups of months were also very wet. No group of months was below the 95th percentile. (See Note 4 below.)

Current drought situation (September 2016)

This month’s rainfall total of 122.4 mm puts it in the 92nd percentile of all monthly rainfall values, far above the median value marked as “normal” on the graph. The 2-month rainfall total (203 mm), and the 4-month rainfall total (350 mm) are almost as high, each in the 90th percentile.
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Manilla’s Droughts, 1884 to 1916

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

Graphical log of droughts, 1884 to 1916

The catastrophic droughts in 1902 and 1912-16 were quite different.

In the years before 1917 shown here, Manilla had several times of extreme drought. They came in 1888, 1895, 1902, and in a cluster that began in 1912.
(1.) The 1888 extreme droughts were of 2-, 3-, 4-, 5-, 6- and 9-month duration. The 2-month event was in August, and other events came later as they became longer, until the 9-month event came in December (having begun in April).
(2.) In 1895, drought was extreme only for durations of 5-months (June) and 6-months (July and August). Although droughts of 2-, 3-, 4-, and 9-month duration also occurred, they were not extreme, but merely “severe”.
(3.) Manilla’s 1902 (“Federation”) drought was phenomenal. Extreme droughts of nearly all durations from 2 months through to 96 months occurred (and ended) at practically the same time. The 2-month event plots at May 1902. The 96-month extreme drought plots at February-March 1903. None of the drought events around 1902 extended far into 1903; all ceased abruptly. The rainfall shortages began earlier according to a simple pattern; the longer the duration of the extreme event, the earlier it began. The 1902 extreme 1-year drought began in September 1901, and the extreme 8-year drought began in 1895.
(4.) The cluster of drought events extending through 1912 and 1916 was as bad as the events of 1902, but quite different. Merely “severe” short-duration events began in April 1911. Events of increasing duration came at later dates, forming a smooth curve on the graph. Beyond 12-month duration, and up to 72-month duration, there were extreme events at nearly all classes of duration. By the 72-month duration, the date of plotting had drifted forward in time to January-July 1916. The beginning of these 72-month events would have been during Continue reading →

The 2002 rainfall shortages at Manilla

Posted in 21st-century climate, Australian Climate, Climate events, Manilla NSW by

Graph of monthly percentile rainfall in a drought

In 2002, Manilla had a 6-month drought with one of the most extreme rainfall shortages on record. In nearly fifty years since 1966 there have been no other shortages like it.

I have discussed this drought in two posts: “Profile of an Extreme Drought”, and 3-year trends to August 2004 (An extreme 1-year drought).

[For an update on the longer and more extreme drought of 2018-19, see the note below.]

This post is about the rainfall record only. It compares the percentile values of rainfall totals for groups of months: one month, two months, and so on. The graph shows how the drought began, developed and faded. Other droughts may go through similar stages. I have plotted the pattern of rainfall shortages month by month, showing only even-numbered months. I have plotted them in different colours, with matching “Call-out” labels.

April 2002 (Red): no drought yet.
In April, the monthly rainfall was slightly below average: in the 40th percentile. In this month, nearly all rainfall totals up to the 42-month total were also below average. Only the 6-month total was above average. This set up the conditions for a drought. Notice that rainfall totals for periods longer than 42 months were all well above average. This hardly changed at all in this year. There had been a lot of rain in previous decades.

June 2002 (Orange): 2, 3, and 4-month droughts.
When May rainfall was in the 1st percentile and June rainfall in the 25th percentile, the June 2, 3, and 4-month totals became serious or severe shortages (below the 10th percentile).

August 2002 (Green): 2, 3, 4, 5, 6, and 9-month droughts.
With July rainfall again in the 1st percentile, and August rainfall in the 26th, the drought became extreme. The 4, 5, and 6-month totals were in the 1st percentile: few months had ever had such low figures.

October 2002 (Blue): 3, 4, 5, 6, 9, 12, 15, and 18-month droughts.
September and October both had rainfall in the 18th percentile. That relieved the short-term shortages somewhat, but not those in the medium term. Shortages in the 4, 5, and 9-month totals were in the 1st percentile, but the 6-month total was very much worse. At 76 mm, this 6-month total was the third driest on record, beaten only by August 1888 (43 mm) and September 1888 (69 mm).

December 2002 (Purple): only 9- and 12-month droughts remain.
November rainfall that was near average (40th percentile) and high December rainfall (84th percentile) broke the drought. Only some longer-term effects persisted as severe rainfall shortages in 9- and 12-month totals.

Rainfall status Jan-Feb 2019

Note added 2019.
Later such graphs in this blog have a logarithmic scale to distinguish the extreme rainfall shortages. Here is the one for the even more extreme drought of February 2019.

Extreme Droughts by Decade at Manilla

Posted in Australian Climate, Climate Change, Manilla NSW, Rainfall from 1883, World Climate by

Extreme droughts per decade at Manilla NSW

The record of extreme droughts at Manilla, NSW, relates to the Southern Oscillation only now and then, and relates to global warming not at all.

This graph shows some of the same data as I presented earlier in the post “Manilla’s Record of Droughts”. The graph there showed precise dates, but it was hard to tell when extreme droughts were more or less frequent. This graph adds up the number of months of extreme drought in each decade. (See Note below: How I count drought months.)

There are separate columns (getting progressively redder) for extreme droughts of duration 3 months, 1 year, 3 years, and 10 years.
Extreme droughts of 10-year duration occurred only in the 1920’s and 1940’s.
Extreme droughts of 3-year duration occurred in the 1910’s, 1940’s, and 1960’s.
Extreme droughts of 1-year duration occurred in the 1900’s, 1940’s, 1960’s and 2000’s.
Extreme droughts of 3-month duration occurred in the 1880’s, 1900’s, 1910’s, 1920’s, 1940’s, 1970’s and 2000’s.
No extreme droughts at all occurred in five of the fourteen decades: the 1890’s, 1930’s, 1980’s, 1990’s, and 2010’s.

[Note added August 2019.

More data for the decade beginning 2010.
This post, dated December 2014, shows no extreme droughts in the decade beginning 2010. Extreme droughts did occurr in 2018 and 2019, as shown in the post “Rain Shortage Jan 2000 – May 2019”.
By August 2019, some months of extreme drought at 3-month and 1-year duration had occurred, and a month at 3-year duration was imminent.]

Relation to the Southern Oscillation Index

I posted this graph of cumulative values of the SOI earlier.

SOI CUSUM plot

The record of the Southern Oscillation Index relates to the Manilla record of extreme rainfall deficiency only now and then. Persistent El Niños from 1911 to 1915 seem to relate to four months in the decade of the 1910’s having extreme 3-year droughts, carrying forward to two months in the 1920’s having extreme 10-year droughts. Similarly, the catastrophic droughts of short to very long duration in the 1940’s relate to El Niños that persisted from 1939 to 1942.
Other major El Niño events did not produce extreme droughts at Manilla: those of 1896, 1982, and 1997.
Long term trends in the Southern Oscillation Index do not predict Manilla’s extreme droughts at all. The 1940’s droughts Continue reading →

Manilla’s Record of Droughts

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

Graph of droughts versus time

In terms of rainfall alone, Manilla, NSW, had droughts between 1900 and 1950 that were more severe, and lasted very much longer than those of recent years.

Comparing droughts

It is hard to say how bad one drought is compared to another because some droughts last longer than others. A drought that lasts two months, and has only 10 mm of rain when it would normally have 100 mm, qualifies as “extreme”. In such a very short drought, rainfall as low as 10% of normal just qualifies as extreme. For a drought lasting twelve months, when there is normally 652 mm of rainfall at Manilla, there has never been a case of a twelve-month rainfall as low as 10% of that (65 mm). (The lowest ever was 288 mm, in 1964-65.) Clearly, using 10% of normal rainfall will not do to define longer-term droughts.
I find the severity of each drought, whether it is long or short, by its percentile rank.
The Bureau of Meteorology defines “Rainfall Deficiency” as:

Lowest on record – lowest since at least 1900 when the data analysed begin.
Severe deficiency – rainfalls in the lowest 5% of historical totals.
Serious deficiency – rainfalls in the lowest 10% of historical totals, but not in the lowest 5%.

On the graph, I use this code:

Extreme rainfall shortage: rainfall in the 1st percentile only.
Severe rainfall shortage: rainfall in the 2nd to 4th percentiles.
Serious rainfall shortage: rainfall in the 5th to 9th percentiles.

Major droughts

All of Manilla’s extreme rainfall droughts that lasted for six years or more happened in the first half of the 20th century. Extreme droughts lasting for thirty years ended during 1940, 1941 and 1947.
Since 1950, the longest extreme drought lasted only five years, ending in 1961. The next longest lasted three years, ending in 1968. The last forty-four years have brought only six extreme droughts, all of less than two years duration: 1971, 1974, 1982, 1984 (2 months!), 1994 and 2002. The twelve years since 2002 may be the longest period without an extreme drought in the whole record since 1883.
Extreme droughts had also been few and short in the earliest years, from 1883 to 1902.

Similar, but much improved graphs

[This graph gives the misleading impression that the longer the duration of rainfall shortage, the later it occurs. That is an artefact.

A shortage of a given duration observed in a particular month must have commenced earlier: earlier by the number of months of its duration, less one.
Graphs that remove this defect, and plot correctly the dates of onset, persistence, and breaking of rainfall shortages are “Rainfall Shortage History: Manilla” and “Rainfall Shortage Jan 2000 – Mar 2019”.

Droughts Elsewhere

At Lake George, in the southern highlands of NSW, extreme droughts of long duration were similarly restricted to the first half of the 20th century, as shown by rainfall records and lake levels.
The “Millennial Drought of southeastern Australia” was not a drought of long duration at either Manilla or Lake George.

[Note added May 2016

Graphical log of droughts, 1884 to 1916The post “Manilla’s Droughts, 1884 to 1916” has an enlarged graph showing more detail. Of the catastrophic droughts of 1902 (“Federation Drought”) and 1912-16, the first had a sudden termination but the second had a sudden onset.]

This blog has many more posts about drought (or rainfall deficiency) at Manilla, NSW. Please use the “Search” function at the top right.

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