Dry and Mild September 2018

Eucalypts dying in drought

White Box Trees Die

Temperatures were near normal, with a number of warm nights. There was just one very cool day that reached only 14.8°. The first 30° day of spring came on the 14th. The early morning dew point on the 17th, minus 10.5°, was the lowest September value, but far from the lowest recorded recently.
There were eight rain days, but the highest reading was only 3.6 mm, on the first day of the month.

Weather log September 2018

Comparing September months

Despite being within an extreme drought, moisture measures this month were not very low; not as low as in September 2017. While the mean temperature was normal, the daily temperature range was low, which is unusual in a drought.
The rainfall total of 12.5 mm (estimated) is at the 18th percentile for September.
I have reported the shortage of rainfall in another post: “Record 15-Month Drought in 2018”.

Climate in September months


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.  The record was again defective in September 2018. No 9am readings were recorded. 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.

3-year trends to September 2018

Equable, less sunny

3-year trends to September 2018

September raw anomaly data (orange)

Like last month, climate anomalies were in retreat from drought. All moisture measures, except rainfall, moved lower on the graphs. Both the daily temperature range and the percent of cloudy mornings recovered from extreme values.

 Fully smoothed data (red)

Fully smoothed data for March 2018 broke the previous month’s record for daily maximum temperature anomaly (x-axis), advancing from +1.58 to +1.63 degrees. The March smoothed rainfall anomaly of −27.1 mm (top left graph) equaled the 20th-century record minus value set in July 2002. Both these records may be broken by fully-smoothed figures for April 2018.
By March 2018, the trend for decreasing rainfall with increasing daily maximum temperature (top left graph) had lasted eight months. Other variables had different patterns. Most were just beginning to move towards drought after several months with little change.
Daily minimum temperature, after six months of sustained rise, then began to fall. Subsoil temperature anomaly was rising, lagging daily maximum temperature anomaly by five months.


Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.
Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

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.

Record 15-month Drought in 2018

The 15 months to date is the driest 15 months in the Manilla rainfall record from 1883.

Rainfall shortages August and September 2018

Graph of Rainfall Shortages

This graph shows all the present rainfall shortages at Manilla, short term and long term, in terms of percentile values. The latest values, as at the end of September, are shown by a black line with black circles. Those from one month earlier, at the end of August, are shown by a thinner line with smaller white circles.

Changes this month

The September rainfall total of 12.5 mm was at the 18th percentile. That raised short-term totals (2-, 3-, and 4-month totals) compared with those of a month ago. However, totals fell very much lower for 5-, 6-, 9-, 15-, 18-, and 24-months.

Extreme shortages

Extreme shortages, seen less than 1% of the time since 1883, are now seen for the durations of 5, 6, 9, 15 and 18 months. This drought is now worse than the drought of 2002. In that drought the longest duration of extreme shortage was only 12 months: 307 mm (at the 0.2th percentile) from December 2001 to November 2002.

A record rainfall shortage

The 15-month total of 400 mm is the lowest in the 136-year record. It is a rate of 26.7 mm per month, 49% of normal, and at the 0.06th percentile. It beats the previous lowest 15-month total of 404 mm that was set in May 1912.
The last time that records for low rainfall were set at Manilla was nearly 50 years ago. Those records were: only 1 mm rainfall in the two months to April 1971, and only 14 mm in the four months to June 1971.

Long-term shortages

The 6-year rainfall total (3244 mm) is a severe shortage, unchanged for three months. These values are lower than any 6-year rainfall totals since 1962. When rainfall shortages of such long duration persist, rainfall does not maintain the groundwater levels or river flows required for irrigation or town supply.
A serious 20-year shortage (9.7th percentile) has developed in this month. Such a very long-term shortage has not been seen since 1949. Up to that date, the Namoi River had suffered decades of low flow, which was followed later by much higher flows. Manilla’s mean annual rainfall has been above normal from 1949 until recently.


Classes of rainfall shortage

I have adopted two classes of rainfall shortage from the classes of “Rainfall deficiency” defined by the Bureau of Meteorology in their Climate Glossary as follows:

“Serious rainfall deficiency: rainfall lies above the lowest five per cent of recorded rainfall but below the lowest ten per cent (decile range 1) for the period in question,
“Severe rainfall deficiency: rainfall is among the lowest five per cent for the period in question.
“Areas where the rainfall is lowest on record for the given time period are also shown.”

The Manilla rainfall record allows me to be more exact than the Bureau. Because the record extends back 134 years, it includes more than 1200 cumulative monthly rainfall values. I can identify percentile ranks even below the 0.1th percentile.
To the Bureau’s two classes of deficiency I add a third:

“Extreme deficiency (or extreme shortage): rainfall lies below the lowest one percent for the period in question.”


Manilla rainfall records

Manilla Post Office rain gauge, Station 055031, was read daily from 1883 to 26 March 2015. Then, for 15 months there was no official Manilla rain gauge. A Bureau of Meteorology automatic rain gauge was re-located to the museum yard and operated as Station 055031 from 23 May 2016 to 7 October 2016 (4 months). It failed, and did not operate for 5 months. After repair, the gauge was read automatically at 9 am daily as Station 055312: Manilla (Museum). It failed again after 6 months, on 24 September 2017. The web-page for Station 055312 shows that, since its repair on 15 March 2018, the gauge has been unreliable, with readings frequently missed. No readings were recorded in September 2018.
Since April 2015, I have read my rain gauge in Monash Street Manilla daily. I have used these readings when official readings are lacking. The gauge is not precise, the site does not meet specifications, and it is 1 km from the Post Office. However, the daily readings are seldom more than 3 mm higher or lower than available official Manilla readings.

Winter 2018 had the driest air

A gum-tree blowing in the wind

Wind-blown Gum-tree

Temperatures varied widely, especially at night. In both mid-July and mid-August, the weekly mean night temperatures were more than 4° low. At these times, the air was extremely dry.
Early in July night temperatures were nearly 4° high, while late in July it was the day temperatures that were more than 4° high. The daily temperature range was almost 21° in mid-July, having been less than 13° in mid-June.
There were 16 rain days, but the highest reading (estimated) was only 10.2 mm.

Weather log for winter 2018

Last winter’s report had been headlined: “Dry air in winter 2017”. This winter was even drier by all measures. In particular, the mean early morning dew point set a new record of -3.0°. The best match in this century is the winter of 2002. Both had warm days, cold nights, wide daily temperature range, little cloud and low dew point.
The total rainfall of 42 mm makes this the 9th driest winter on record, displacing winter 2002, which had 44 mm. (The year 1888 had the lowest winter rainfall total: 6 mm. However, daily readings are missing. The next lowest was 1946, with 29 mm, then 1972 and 1982, both with 32 mm.)

Climate for winter 2018


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. During this winter season 20 daily readings were missed, including several days with significant falls of rain. I have used my own readings for the whole season.

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

Driest Air in August 2018

Tree with a face painted on it.

Painted Box Tree

Temperatures were not far from normal during the month, except that the weekly mean was 3.2° low about the 20th. There were 20 frosts (normally 15), but the coldest morning fell only to -2.7°.
Some rain fell early in the month. Later, with the cold nights, the air became extremely dry, reaching a new record early morning dew point of -12.1°. Abruptly, the 25th brought overcast and high humidity, then rain and fog. Estimated rain was 9.0 mm on the 26th, 10.2 mm on the 27th, and 0.8 mm on the 28th.

Weather log August 2018.

Comparing August months

The month was rather cool, with a mean (10.7°) that was 0.4° below normal, and cold nights (2.0°), 1.1° below normal. Measures of moisture were only slightly low, except that humidity was extremely low, setting a new record mean early morning dew point of -4.2°.
Moderate falls of rain totalled 28.2 mm (estimated), which is at the 40th percentile for August.
I have reported the shortage of rainfall separately ( “Drought Sixth Month: August 2018”) .

Climate in August months.


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.  The record was again defective in August 2018. Seven daily readings were missing. On one of the missing days (the 27th) my rain gauge showed 10.2 mm, the highest daily reading for the month. I have substituted my non-standard gauge readings for all days of both July and August.

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

Drought Sixth Month: August 2018

Rainfall status, July and August 2018.

Graph of Rainfall Shortages

This graph shows all the present rainfall shortages at Manilla, short term and long term, in terms of percentile values. The latest values, as at the end of August, are shown by a black line with black circles. Those from one month earlier, at the end of July, are shown by a thinner line with smaller white circles.
The classes of rainfall shortage are:
• Serious shortage: below the 10th percentile;
• Severe shortage: below the 5th percentile;
• Extreme shortage: below the 1st percentile. [See note below on my usage “Extreme shortage”.]

Changes this month

Rain late in August raised the one month and two month rainfall totals out of the class of “serious shortage”. The total for August (28.2 mm) is at the 40th percentile for the month, and the total for July and August is at the 10th percentile. The three-month total, which had been an extreme shortage, fell to become only a severe shortage.

Extreme shortages

Extreme shortages, seen less than 1% of the time since 1883, are now seen for the durations of 4, 5, 6, and 15 months. Without last week’s rain, the 6 month total would have been one of the lowest ever recorded.
There is an extreme shortage at 15 months, due to low rainfall in mid-2017, in the months of July (13.2 mm), August (13.8 mm), and September (5.5 mm).

Long-term shortages

The 6-year rainfall total for August (3252 mm) is a severe shortage, only slightly above that of July (3234 mm). Both these values are lower than any 6-year rainfall totals since 1962. When rainfall shortages of such long duration persist, rainfall does not maintain the groundwater levels or river flows required for irrigation or town supply.

[A graph showing rainfall shortages to the end of September 2018 is in the later post: “Record 15-month Drought in 2018”.]


Note: The term “Extreme shortage”

I have adopted classes of rainfall shortage from the classes of “Rainfall deficiency” defined by the Bureau of Meteorology in their Climate Glossary as follows:

“Serious rainfall deficiency: rainfall lies above the lowest five per cent of recorded rainfall but below the lowest ten per cent (decile range 1) for the period in question,
“Severe rainfall deficiency: rainfall is among the lowest five per cent for the period in question.
“Areas where the rainfall is lowest on record for the given time period are also shown.”

The Manilla rainfall record allows me to be more exact than the Bureau. Because the record extends back 134 years, it includes more than 1200 cumulative monthly rainfall values. I can identify percentile ranks even below the 0.1th percentile.
To the Bureau’s two classes of deficiency I add a third:

“Extreme deficiency (or extreme shortage): rainfall lies below the lowest one percent for the period in question.”

3-year trends to August 2018

Cooler and Moister

3-year trends to August 2018

August raw anomaly data (orange)

For now, a retreat from drought is shown by lower temperature, particularly at night, and more rain. Dew point remains very low.

 Fully smoothed data (red)

The summer season, ending in February 2018, can now be fully smoothed. February has a new 21st century record [in blue] for smoothed daily maximum temperature anomaly of +1.58° [x-axis all graphs]. This is bound to be broken by smoothed values for March, and perhaps for April. The record for negative rainfall anomaly (set in the drought of July 2002) is also likely to be broken in March.

Through the summer, all three temperatures rose, and rainfall fell. Other variables were static.


Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.
Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

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.