Tag Archives: Manilla

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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October 2014 hot and dry

Posted in Manilla NSW, Monthly weather by
Blooms of Melia azedarach

Fragrant white cedar blooms

The month began with a warm spell, which was followed by a cool spell about the 15th. It ended with a long hot spell, 4.8 degrees above normal, including the hottest October day this century (38.1°) on the 26th. As usual, there were no frosts.

Of three rain days (usually seven), only the 14th had much rain: 26.4 mm, with heavy showers.
Half the mornings had no cloud at all, and nine days had very wide temperature ranges, greater than 20°.

Weather log October 2014

 Comparing October months

This was the hottest October month at Manilla in this 16-year record. Maximum, mean and minimum temperatures were all highest values, but the maximum was no higher than in October 2007. The subsoil temperature returned to a value below normal.
As indicators of low moisture, the daily temperature range was very high and cloudiness and dew point were very low, as in the last two October months. Even less cloud had been seen in 2002 and 2004.
Recently, lower rainfall occurred in October 2002 (15.0 mm), 2012 (12.6 mm), and 2013 (15.0 mm). However, this month’s total of 27.0 mm is well below the October average of 58 mm, in the 21st percentile. Since last month, little has changed in rainfall totals for periods of more than one month. There is still a serious shortage in the 6-month total (8th percentile) but not now in the 9-month total (10th percentile). The 15-month total has advanced to severe (4th percentile), while the 18-month total has retreated to serious (5th percentile). A serious shortage has also appeared in the 30-month total (8th percentile).

Climate October 2014  

Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Temperatures, including subsoil at 750 mm, and other data are from 3 Monash  Street, Manilla.

3-year trends to October 2014

Posted in 3-year climate trends, Manilla NSW by

Parametric plots of smoothed climate variables at Manilla
“October 2014 droughty”

Trends to October 2014

October data (orange)

All raw anomaly values for October, except subsoil temperature, moved suddenly to drought: high temperatures and little moisture. Subsoil temperature, which had been at a record high value fifteen months earlier, became very low.

Fully smoothed data (red)

The latest fully-smoothed data (April 2014), like that of the previous month, continued the trends established in summer. All (except daily minimum temperature) moved away from drought. A movement back towards drought came only later.
Since the major “flooding rains” episode of summer 2011-12, (lower left corner on the graphs)  Manilla’s climate has swung towards drought three times:
(i) a very mild drought in October 2012, returning to normal by March 2013;
(ii) a moderate drought that was very hot in October 2013 and dry in January 2014, returning to normal about May 2014;
(iii) perhaps a further drought about October 2014 (to be identified later).

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.

October Climate Anomalies Log

Posted in 21st-century climate, Calendar month anomalies, Climate Change, Manilla NSW by

Heat Indicators log for October months

This post is the eighth in a set for the 12 calendar months that began with March. Graphs are sixteen-year logs of the monthly mean anomaly values of nine climate variables for Manilla, NSW, with fitted trend lines. I have explained the method in notes at the foot of the page.

This series of posts gets more than its share of views. This is strange, as they contain little information. Comparing graphs for adjacent months shows widely different values and trends. In due course, I will compare all twelve months with each other. Perhaps that will yield interesting results, or perhaps not.

Raw anomaly values for October

Extreme values of October anomalies in this period were all in the “Moisture Indicators” group:

Cloudy days % anomalies (2) +31%: October 2010, 2011;
Dew Point Anomalies (5) +3.9°: October 1999, -3.9°: October 2002, -6.6°: October 2012, -7.8°: October 2013, -5.9°: October 2014.
Moisture Index (2) -3.1°: October 2012, -3.2°: October 2013.

Trend lines for October

Heat Indicators

The trend lines of daily maximum, mean and minimum temperature anomalies all had an early trough in 2001, a peak near 2006, and a trough near 2011. The daily minimum trend had the longer period and the larger amplitude. The subsoil temperature trend peaked early, in 2001, and had a very broad trough around 2009.

Moisture Indicators log for October months

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Decadal and Inter-decadal changes in rainfall: III.

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

Summer rainfall anomalies and trends

Part 3 of 3: A growth and collapse model for summer rainfall

(See Notes below for data and plotting details.)

I have put this October 2014  post up on the front page as a “sticky” (5/1/15) because I have just found a relevant scientific article. See “Note added January 2015” below.

A linear trend

In Part II, I showed that a linear trend fits well (R-squared = 0.54) to smoothed summer rainfall at Manilla, NSW from 1897 to 1976. This trend-line rises extremely steeply: 156 mm per century.
(See also the Duodecadal Means graph below.)

Implications of the extreme trend

Such an extreme trend cannot extend more than a short time into the past or the future without reaching physical limits. Extremely high values must be followed by lower values and vice versa. The oscillation between higher and lower values in nature is often modeled as a smooth harmonic curve. That does not fit well here. Not only does the rise from 1897 to 1976 fail to curve down approaching the final peak, the falls from 1892 to 1900 and from 1975 to 1987 are extremely sharp. They are collapses.
It seems to me that a model of steady growth followed by sudden collapse may perhaps reflect the processes involved. On the graph I have added speculative trend lines of the same rising slope as that observed for 1897 to 1976. The constant for the first speculative trend line is 130 mm higher and leads to a 130 mm collapse from 1896 to 1899. A 90 mm collapse from 1978 to 1981 then leads to a renewed rising trend that is 90 mm lower.

Note added January 2015.

The sudden collapse in summer rainfall here at the beginning of the twentieth century was studied sixty years ago by E.B. Kraus (Snowy Mountains Authority!): “Secular changes of east-coast rainfall regimes” (1955).
“The mean rainfall along the east coasts of North America and Australia is shown to have decreased abruptly at the end of the 19th century… A simultaneous decrease of the rainfall in the Continue reading →