December 2017 as in 2016

Blooms of San Pedro Cactus at Manilla NSW

San Pedro Cactus 2017

The weather in this December was very like the weather a year ago. Even details were similar. Each had just one 40° day. Each had one night near 25°, about 9° above normal. This December had one hot spell 6.3° above normal: last December had two hot spells 4.8° and 3.6° above normal. Neither had cool spells.
This December’s highest rainfall reading, 15.5 mm (unofficial), was like last December’s 17.8 mm (also unofficial). This month had fewer rain days (5 vs. 12) and longer dry spells.

Weather log for December 2017

Comparing December months

This was one of the hottest Decembers in the new century. The mean daily maximum, at 33.7°, equals that of December 2005, but is beaten by 33.8° last December. The mean daily minimum, at 18.2°, equals that of last December, but is not as warm as the 18.6° of December 2009. By contrast, December 2011 was the coldest, with a mean maximum of only 27.0°, and a mean minimum of only 13.9°.
This month’s subsoil temperature (23.0°) was very cool; one of four December values more than a degree below normal.
Like last December, this month was not very moist, but not very sunny either.
The rainfall of 48.2 mm was practically the same as in December 2016 and 2013. It is at the 35th percentile: not high, but high enough to prevent shortages.

Climate in December months

The Year 2017 was warm and dry

In this record (2000 to 2017), Manilla’s average annual temperature this year (18.65°) shows it to be the third warmest, after 2014 (19.01°) and 2009 (18.85°). The coolest was 2008 (17.19°), which was also cool globally. (Apart from 2008, Manilla annual temperatures do not follow global temperatures closely: the hottest year globally (2016) was not a very warm year here.)
Like the previous two years, 2017 had night temperatures half a degree below the normal value. Day temperatures, which had been near normal in 2015 and 2016, became a degree warmer. This year’s subsoil temperature (19.80°) was cool, very much cooler than in 2013 (22.19°).

It was a year of very low rainfall: 517 mm, which is at the 20th percentile, and 135 mm below the average (652 mm). Three even lower rainfall totals have occurred in the last sixteen years: 366 mm in 2002 (2nd percentile), 495 mm in 2009 (16th percentile), and 447 mm in 2014 (8th percentile).
Manilla yearly rainfall history: four momentsThis unusually high ratio of very dry years agrees with other patterns seen in Manilla’s annual rainfall. That is, in the moments of the frequency distributions. Recently, Manilla’s annual rainfall has had (i) very high kurtosis, showing increased extremes (“fat tails”), and (ii) negative skewness, showing that these extremes are low extremes, not high extremes.


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, but it is not.  The gauge last reported on 24 September 2017.

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

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3-year trends to December 2017

Hot days and nights

3-year trends to December 2017

December raw anomaly data (orange)

December 2017 had hot days and hot nights, but the subsoil remained cold. Rainfall was low, while other measures of moisture were near normal.

 Fully smoothed data (red)

The latest fully-smoothed data point is for June 2017. By that time, all variables were within the normal range except for dew point. Even dew point was in the centre of the range of low values that has become “normal” since 2010. Three variables were static: daily maximum temperature, subsoil temperature, and rainfall. Cloudiness, dew point, and daily temperature range. were moving towards aridity. Daily minimum temperature was falling.


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.

Rainfall kurtosis vs. HadCRUT4 Scatterplots

These scatterplots and Connected Scatterplots support a relationship between the kurtosis of annual rainfall at Manilla NSW and the de-trended smoothed HadCRUT4 series of global temperatures.

Scatterplot rainfall kurtosis vs. HadCRUT all data

The raw data, as observed

The first scatterplot compares (y-axis) all the calculated unsmoothed values of kurtosis of annual rainfall at Manilla, NSW with (x-axis) the unsmoothed values of the HadCRUT4 series of global near-surface temperature at those dates.
[I have plotted rainfall values lagged by five years on all of the scatterplots shown. This lagging makes little difference to the first two scatterplots.]

On this first graph, the fitted linear trend barely supports a positive relation of kurtosis to temperature. The slope is low (1.05) and the R-squared only 0.16. There is an aberrant cloud of points in the top left corner.

Scatterplot rainfall kurtosis vs. HadCRUT detrended (all data)

The raw data, HadCRUT4 de-trended

This graph takes a first step towards a better model for the relationship: the secular trend of the temperature series (that is, the global warming) is removed. For comparison, I have not re-scaled the x-axis.
Although still very weak, the relation is much enhanced. The slope (2.35) is twice as steep and the R-squared (0.24) increased by 50%.

Connected Scatterplot rainfall kurtosis vs. HadCRUT all data

Smoothed data, HadCRUT4 de-trended

This third graph uses smoothed data. The HadCRUT4 series is  “decadally-smoothed” (as published) with a 21-point binomial filter to remove high frequency noise. The rainfall data, already damped by its 21-year sampling window, has been further smoothed with a 9-point Gaussian filter.
This graph is a Connected Scatterplot, that shows the trajectory of the rainfall-temperature relation with the passing of time.

Line chart rainfall kurtosis vs. HadCRUT (detrended)Smoothing both data sets has given a much closer relation. The R-squared value is almost doubled again, to 0.43, and the slope is increased to 3.70. The date labels show that the relation before 1910 was different from that at later dates. (This had also been clear in the Dual axis line chart, copied here, from the post “Rainfall Kurtosis Matches HadCRUT4”.)

Connected Scatterplot rainfall kurtosis vs. HadCRUT from 1908

Smoothed data, HadCRUT4 de-trended, from 1908 to 2002

In this final graph, I have discarded the first eleven years. The linear regression based on smoothed values from 1908 to 2002 has a steep slope of 5.21 and a respectable R-squared value of 0.84.

I had prepared similar graphs for lag values of rainfall kurtosis from zero up to nine. The lag value of five years tends to maximise the slope and the R-squared values.
Choice of a five-year lag tends to form hair-pin loops in the trace, while shorter lags give wider clockwise loops and longer lags give wider anti-clockwise loops.
The lag value of five years implies that the Manilla annual rainfall kurtosis value for a given year matches the de-trended HadCRUT value that occurs five years later.

Rainfall kurtosis matches HadCRUT4

Line chart rainfall kurtosis vs. HadCRUT (detrended)

The kurtosis of annual rainfall at Manilla NSW forms a time-series that matches the time-series of global surface temperature when de-trended.

Features of the data

Data sources, noted on the graph, are specified below. The best match is achieved by decadal smoothing, by scaling 1.0 units of kurtosis to 0.16 degrees of temperature, and by lagging the rainfall data five years.

Closeness of the match

Although both variables have irregular traces, their patterns are almost the same. They begin and end very high, have a broad peak near 1943, and are low in the 1910’s, 1920’s, 1950’s, 1960’s and 1970’s.
The match is very close for ninety years from 1915 to 2005, except for one decade (at 1972). In all this time, both the values and the slopes (as scaled) agree. [See the Note below “1991-1992”.]

Before 1915, the patterns do not match well, but they remain similar. Both traces descend rapidly together from 1903 to 1910. The initial peak in the rainfall trace at 1903 (actually 1898) is similar in height (as scaled) to a peak of the de-trended temperature trace just off the graph at 1879.

Discovering the pattern match

I was seeking a robust measure of the occurrence of extreme values in annual rainfall at Manilla, NSW. As kurtosis is just such a measure, I calculated it. I then plotted out the time-series, as shown here. It reminded me of the well-established time-series of smoothed HadCRUT4 global near-surface temperature. In particular, I recalled a locally-dominant peak near 1940.

Line chart rainfall kurtosis vs. HadCRUT
Simply reconciling the vertical scales of the two time-series gave me the second graph.
While not matching in details, the two curves remain very close from 1940 to 1995. Matching over the whole rainfall record is prevented by a difference in trend. While the rainfall kurtosis has no trend, the HadCRUT4 curve has a secular trend rising at half a degree per century (known as “global warming”).
To extend and improve the match, I subtracted the linear trend from the global temperature curve, and lagged the rainfall points by five years. The first graph is the closely-matching result.

What it means

As evidence of extreme behaviour in climate

It is said that more extremes in climate will occur as the world becomes warmer. The evidence is not strong. Most data sets are overwhelmed by noise, and “extreme” is seldom defined with rigor.
In the present case, I believe that the definition of “extreme” that I use is sound: that is, the kurtosis of a frequency-distribution. Only the instability of kurtosis when based on small samples is an issue.

My rainfall data set that displays more and less extreme behaviour is not general but local. It can merely suggest that data elsewhere may reveal functional relationships.

Connected Scatterplot rainfall kurtosis vs. HadCRUT from 1908A very strong and persistent empirical relationship is shown by the graphical logs above. In another post, “Rainfall Kurtosis vs. HadCRUT4  Scatterplots”, I show scatterplots like this in support of it.

De-trended global temperature

This strong link between local annual rainfall kurtosis and global climate has a surprising feature. Although this extreme behaviour seems to relate to global temperature, it does not relate to global warming! It relates to a temperature trace from which the global warming trend has been removed. Times of high kurtosis, denoting enhanced extremes, correspond to times when the global temperature was highest above trend. Such times occurred not only in the twenty-first century, but equally in the nineteenth century. There was another (widely-known), lower peak in de-trended global temperature near 1940: at that time also kurtosis was above normal.

Should global temperature remain static for a time, it would be falling rapidly below its rising trend. According to this data set, that should bring reduced extreme behaviour in annual rainfall at Manilla.


Data Sources

(i) Global temperature time-series

From the three available century-long time series of global near-surface temperature I have chosen to use HadCRUT4, published by the British Met Office Hadley Centre. The link is here.

I selected from the section: “HadCRUT4 time series: ensemble medians and uncertainties”.
From this, I downloaded two files:
(i) “Global (NH+SH)/2, annual”;
(ii) “Global (NH+SH)/2, decadally smoothed”.
[The “Decadally smoothed” data supplied is annual data smoothed with a 21-point binomial filter.]
From each data file, I used only the first column: the year date, and the second column: the median value.

I established the secular trend of global warming using the linear trend function in Charts for “Excel”. I found the linear trend of the whole HadCRUT4 annual series data (1850 to 2016) to be:

y = 0.005x – 0.52.

I then subtracted the annual value at the trend line from the decadally smoothed HadCRUT4 value to get the de-trended smoothed value shown on the first graph.

(ii) Kurtosis of Manilla annual rainfall

The rainfall data is that for Manilla Post Office, Station 055031 of the Australian Bureau of Meteorology. Station 055031 functioned without gaps from 1883 to March 2015. Since then, the official record is fragmentary.
I found kurtosis values for annual rainfall by using the (excess) kurtosis function in “Excel”. I used sub-populations of 21 successive years, referred to the median year. I found values for the years 1893 to 2006. I smoothed these values with a 9-point gaussian filter (yielding similar smoothing to that of HadCRUT4). Smoothing reduced the plottable years to those from 1897 to 2002.

Manilla yearly rainfall history: four momentsI posted a line graph of this kurtosis data earlier, in “Moments of Manilla’s Yearly Rainfall History”.


Note: 1991-1992

The most striking match in the graph is that both traces pause at 1991-1992 within a two-decade-long steady rapid rise. That pause in the global temperature series has been attributed with little doubt to the injection into the atmosphere of seventeen million tonnes of sulphur dioxide by the eruption of Mount Pinatubo in the Philippines. That eruption cannot have affected the rainfall kurtosis five years earlier.

Spring 2017 slightly dry

Photo of a Persian silk tree at Manilla NSW

Persian silk tree

Each year, the weather warms by about eight degrees during the three months of spring. This time, the warming came all at once. After cold nights at first, by the third week of September both days and nights were five degrees above normal. As extremes, one day reached 34° and one night 22°. After that, the temperature rose no higher through to the end of the season. By then, such temperatures are normal.

For much of the season, the air was dry, but a humid spell in October brought 63 mm of rain within four days. The season’s rainfall of 134 mm was at the 40th percentile, about 30 mm below average. Other measures of moisture were slightly low.

Graphical weather log for spring 2017

Air temperatures were near normal, with days slightly warm and nights slightly cool. Spring last year had been two degrees cooler, and spring 2014 two degrees warmer. The subsoil temperature was more than a degree below normal, as it often has been in the last two years.

Climate for spring 2017


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. That gauge failed (again) on the 25th of September 2017, and later readings are from my non-standard gauge.

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

November 2017 dry again with cold nights

Cockatoos feeding in a wattle

Corellas in Acacia decora

While day temperatures were normal, many nights were below normal, around 10°. The cold night air was extremely dry. The early morning dew point on the 1st was minus 3.6°, about 14° below normal.
My rain gauge registered seven rain days, but readings were moderate, the highest being 14.0 mm on the 30th. (The automatic gauge at the Museum remained down.)

Weather log for November 2017

Comparing November months

With a mean of 20.8°, this month was cool, but not as cool as several other November months. November 1999, at 19.4°, was the coolest. On the graph, November 2014 (25.4°) stands out as very much warmer.
The rainfall of 44.2 mm is at the 31st percentile: not high, but enough to prevent any shortages. This graph still includes November 2011, the wettest on record. At 242.9 mm, it beat a record of 226 mm that had stood for fifty years.

Climate log for November


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 gauge last reported on 24 September 2017.

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

3-year trends to November 2017

Dry with cold nights

3-year trends to November 2017

November raw anomaly data (orange)

November 2017 reverted to the anomalies of August and September: low moisture (top four graphs) and cold nights (bottom left), with continuing cold subsoil (bottom right). Day temperature (x-axes)had cooled to normal since September.

 Fully smoothed data (red)

Anomaly data for autumn 2017 (MAM) are now fully-smoothed, plotted in red. That season was near the centre for the last three years, but day temperatures fell from high towards normal (seen best on the top right graph). Meanwhile, moisture measures disagreed somewhat. Rainfall rose towards normal, cloudiness decreased towards normal, dew point fell through low values, and daily temperature range was static near normal.
Daily minimum temperature fell towards normal, and subsoil temperature rose to normal.


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.