Rainfall shortage: series of contour plots

This graph is one of a series. All are copied here.

Sequence of rainfall shortages to May 2019

Twenty-five months to May 2019.

The above graph is described here.

Sequence of raiinfall shortages to April 2019

Twenty-five months to April 2019.

The above graph is described here.

Sequence of raiinfall shortages to March 2019

Twenty-five months to March 2019.

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Another warm autumn, 2019

Lake Keepit very low

Keepit Dam at 0.9%

This season had a series of warm spells separated by normal autumn temperatures. The warmest, about 4° above normal, came in early March, late April and late May. Dry air came at cooler times, near the 1st of March and the 12th of April. Most of the rain came in two very wet days: the 30th of March and the 4th of May (61 mm).

Weather log autumn 2019

Comparing autumn seasons

As in 2018 and 2016, autumn was very warm. Although autumn 2016 had the highest mean temperature of the new century, this autumn had the warmest nights: 12.7°.
Despite the on-going drought, measures of moisture were near normal for the season. Cloudy days reached 37%, the daily temperature range (14.3°) was quite narrow, and the early morning dew point (7.2°) not low. The rainfall total, 117 mm (est.), was at the median value, not far below the mean of 134 mm.

Manilla clmate for autumn

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 autumn. I used my own readings for the whole season.

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

Rain Shortage Jan 2000 – May 2019

Record of rain shortages Jan 2000 May 2019

The current drought now has a severe rainfall shortage of 240 months duration that must have commenced in 1999.

[For explanation of this graph, see below: “About drought duration graphs”.]

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 longer-term extreme shortages from 9 months up to 30-months.
In months since November 2018 none of the short-term rainfall totals for durations from two months to six months has been even a severe shortage. In other respects, the drought has deepened. Because recent monthly rainfall values have seldom risen above normal, periods of severe or extreme shortage have become longer and longer. As at May 2019, extreme shortages prevail at 15-, 18-, 24-, 30-, 72- and 84-month durations.
Severe shortages have developed at even longer durations, at 96-, 120-, 150- and 240-months. As is clear from the graph, the 240-month severe shortage incorporates the 2002 drought into the 2018 drought. This was not evident until now.
As shown, the severe shortages of 150- and 240-month duration, current in April 2019, did not persist in observations for May. They could resume if later months do not have much rain.

Drought record to May 2019

Compete record updated to May

When the graph of the complete record of months of rainfall shortage at Manilla is updated to May 2019 it is obvious that the current drought is one of the great droughts in history.
Although this drought seemed to have a sudden onset, shortages of longer duration actually began earlier: the longer the duration concerned, the earlier its time of onset.. The 2018 pattern is like the droughts of 1902, 1940 and 1946. Droughts that actually had a sudden onset were those of 1912, 1957 and 1966.

About drought duration graphs

These graphs show the onset, persistence, and breaking of episodes of extreme and severe rainfall shortage (droughts) at Manilla. The first shows detail since 2000. The second shows the complete historical record from 1884. 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 of observed cumulative rainfall deficiency. Future observations may make any point to the right of this line more extreme.

Rainfall Shortage Sequence 05/2019

Sequence of rainfall shortages to May 2019

Black shows the driest or second-driest rainfall totals. In a record of more than 1600 months, they fall below the 0.1th percentile.

This contour plot shows the progress of the drought at Manilla up to May 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)

This month (May 2019) like March, had rainfall above normal, but April had no rain. Months of serious rainfall shortage (light brown) had come much earlier, in May, June and July 2018, and also in 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. March 2019 included no shortages (not even “serious” ones) for durations from 2 months up to 6 months. April saw some serious shortages return, but they were gone by May.

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 at that time (400 mm). In January 2019, extreme shortages were current at 15-, 18-, and 24-months. By that time, some dry months in 2017 were excluded from the totals, but dry months in the current summer were included.
In February 2019, as the extreme shortages of the previous month persisted, the 12-month total became the driest ever (271 mm). March also had four extreme shortages in this group, but now they were at 12, 15, 24 and 30 months.
April saw lowest-ever or second-lowest values for all durations from 12 months to 30 months. In May, they persisted for 15-, 24-, and 30-month durations.
New lowest-ever values increased the percentile ranks of several earlier values that had been lowest-ever. For example, the 15-month total in September 2018 began as a lowest-ever value with percentile rank below 0.04% but, being replaced by new lowest-ever values in April and May, became third-lowest, with percentile rank 0.12%.

A line graph for May 2019

A profile of the rainfall status for May 2019 reveals that extreme shortages also exist at durations much longer than shown in this contour graph: 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 a recent line graph (April 2019) I have described my method of analysis and its limitations.

May 2019 had the warmest nights

Keepit Dam boom, May 2019

The month began warm, with the night of the 2nd being, at 18.0°, the warmest May night of the new century. There was a second warm spell nearly four degrees above normal about the 20th.
The first frost (by my reading) came on the 12th of May this year, and on the 15th of May last year. The middle date of first frost is May 13th.
There were three rain days (usually four) but nearly all the rain (61 mm) was recorded on the 4th.

Weather log May 2019

Comparing May months

The mean temperature this month (14.6°) was high, but not as high as in May 2007 (15.1°). However, the mean daily minimum temperature (8.1°) was the warmest for May in the new century: above normal by 2.3°.
A rather narrow daily temperature range (13.1°) and high percentage of cloudy days (45%) showed moisture above normal.
The (estimated) rainfall total of 61.8 mm was very high, in the 75th percentile. Because no rain at all had fallen in April, the total for the two months together reached only to the 26th percentile.

Climate for May 2019


The on-going unprecedented drought is reported in another post.

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 2018, 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.

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

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3-year trends to May 2019

May days not warm

3-year trends to May 2019

May raw anomaly data (orange)

In May 2019, the anomaly of daily maximum temperature returned to zero after years of positive values. Both daily minimum temperature and subsoil temperature anomalies were very high. Moisture anomalies, reflecting the high rainfall value (+21 mm), were low on the graphs (away from drought), but dew point was not as far down as “normal”.

 Fully smoothed data (red)

Fully-smoothed data now include the spring season ending November 2018.
Both daily maximum and daily minimum temperature anomalies were very high and rising. The minimum was rising faster and broke the record of +1.65°. Subsoil temperature anomaly, due to a phase lag, was normal and still slowly falling.
Moisture indicators in this spring were inconsistent. Rainfall anomaly decreased slowly to a new (20th century) record of minus 29.7 mm. The dew point anomaly was also low, but rapidly increasing. Both the cloudiness and the daily temperature range were normal.


January data points are marked by squares.


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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