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 1883. 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

In the first of two tables, 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

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”.

3-year trends to February 2019

February arid

3-year trends to February 2019

February raw anomaly data (orange)

By February 2019, temperatures had returned from very high to normal. Rainfall remained very low, and dew point also became very low.

 Fully smoothed data (red)

Fully smoothed data to August 2018 showed that several trends for the spring were typical of drought:

Maximum temperature anomaly was steadily falling from the record high in March.
Minimum temperature anomaly was a little high and steady.
Subsoil temperature anomaly was falling towards normal from a low peak in June.
Rainfall anomaly was near the record low (smoothed) and steady.
Cloudiness anomaly was near zero.
Dew point anomaly was near the record low (smoothed) and steady.
Temperature range anomaly peaked rather high in July, then fell.

More recent data, only partially smoothed, suggest that temperatures and rainfall have since 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.

Fully smoothed data points are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange.

Limiting values

Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

 * Normal values for rainfall are based on averages for the 125 years beginning 1883.

Driest 6 years since 1903

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”.

3-year trends to January 2019

January very hot

3-year trends to January 2019

January raw anomaly data (orange)

In January 2019, the daily maximum temperature (x-axes, all graphs) and daily minimum temperature (lower left graph) were extremely high, while the subsoil had warmed to normal. Rainfall was very low, while cloudiness, dew point and daily temperature range were near normal.

 Fully smoothed data (red)

By July 2018, the last date for which data can be fully smoothed (as described below), variables had already peaked, or were about to peak, in their contribution to an extreme drought.

More recent data, only partially smoothed, suggests that temperatures and rainfall have since 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.

Fully smoothed data points are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange.

Limiting values

Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

 * Normal values for rainfall are based on averages for the 125 years beginning 1883.