Archive for the ‘weather forecasts’ Category

TC Debbie

March 29, 2017

TC Debbie hit the Whitsunday coast and areas to the south and inland yesterday.  As I spent nearly half my life in places not far from Mackay and have many friends in the region, I was very interested to see what was happening.   I began checking online from 5 a.m. Tuesday morning.

Here is some initial analysis of TC Debbie.  Firstly, here is the table of cyclone intensities as found at http://www.bom.gov.au/cyclone/faq/index.shtml#definitions .

Fig. 1:  Cyclone Intensity

TC Intensity

I began checking online from 5 a.m. Tuesday morning.

Fig. 2:  0500 forecast cyclone track map.

Debbie 5am

How accurate was the Bureau’s forecast?  Here is the forecast 22 hours later, at 0300 Wednesday morning.

Fig. 3:  Wednesday 0300 forecast cyclone track map.

Ex TC Debbie

The track forecast was pretty good.

The next images show Debbie’s progress across the Whitsunday Islands until the eyewall crossed the coast near Airlie Beach.

Fig. 4:  0720 Eyewall about to hit Hamilton Island

radar 720am debbie hayman is eye

Fig. 5:  0910  Hamilton Island near the eyewall, Hayman Island in the eye

radar 910am debbie hamilton eyewall

Fig. 6:  10.30  Hamilton Island near the eyewall, Hayman Island in the eye, and the eyewall about to pass over Airlie Beach

radar 1030am debbie hamilton eyewall

And four and a half hours later, the worst is over at Hamilton and Hayman Island and the eye is collapsing over Proserpine.

Fig. 7:  1510  Debbie weakening near Proserpine

radar 310pm eye breakup

Note the “gap” in the image in the northwest sector.  The Bowen radar failed and the Mackay radar was blocked by high mountains to the west.

What about forecasts of the cyclone’s intensity?

The next figures show plots of wind gusts, pressure, temperature, and rain at Hamilton Island, Proserpine, and Bowen, the closest stations to the cyclone’s track.

Fig. 8:  Wind gusts at Hamilton Island

wind hamilton

The black line shows the period from just before 8.00 a.m. until about 2.30 p.m. during which Hamilton Island was close to the eyewall, the area of maximum wind strength.   For nine hours from before 6.00 a.m. until nearly 3.00 p.m. wind gusts were of Category 3 strength.  From 8.00 a.m. until 12.30 p.m. gusts approached or exceeded 225 km/hr, bordering on category 4, and between 10.35 and 10.30 reached 263 km/hr three times at least- and the Bureau had forecast winds up to 270 km/hr.  While the station at Hamilton Island is too high to be completely reliable, these data are indicative that winds at 10 metres were at cat 4 level for some time.

Fig. 9:  Air Pressure at Hamilton Island

pressure hamilton

The red line shows the period from just before 8.00 a.m. until about 2.30 p.m. during which Hamilton Island was near the eyewall, the area of maximum wind strength.    From 2.00 a.m. until 5.00 p.m.  pressure was below 985 hPa (Cat, 2) and from 10.00 a.m. until 1.30 p.m. was below 970 hPa (Cat.3) but did not reach 955 hPa (Cat. 4).  Remember however that Hamilton Island was some 50 km from the centre of the eye, so 955 hPa is quite possible for central pressure.

On the basis of wind gusts and pressure at Hamilton Island, I believe Debbie was a strong Category 3, weak Category 4 system.

Fig. 10:  Air temperature at Hamilton Island

T hamilton

Note the sudden jump in temperature from 8.12 a.m.- 3 degrees in 3 minutes- coinciding with a wind gust of 212 km/hr, and kept climbing to unbelievable values.  (Compare with Proserpine below.)  It is likely that the AWS probe malfunctioned, and failed altogether at 12.00 noon.

Fig. 11:  Rain at Hamilton Island

rain hamilton

Rain measurement is unlikely to be accurate in such ferocious winds.  Note how rainfall levelled off from 11.00 a.m until 2.00 p.m., then increased after 3.00 p.m.

Fig. 12:  Wind gusts at Proserpine

wind proserpine

Proserpine Airport is some 20 km inland, 41 km west of Hamilton Island and 56 km from Bowen.  As the cyclone arrived over land it began losing strength and the eye began to shrink.  From 10.00 a.m. until 2.00 p.m. gusts were at Category 2 strength and at 1.00 p.m. reached the magic 165 km/hr of Cat 3 strength.  They were very probably much stronger in the town itself 9.1 km north.

Fig. 13:  Pressure at Proserpine Airport

pressure proserpine

From 12.30 p.m. until 5.00 p.m. the pressure at the airport, some 20-30 km from the centre, was below the Category 3 value of 970 hPa.

Wind gust and pressure data indicate Debbie was very likely still Category 3 as it passed over Proserpine town.

Fig. 14:  Air temperature at Proserpine

T proserpine

Fairly stable temperature with only about 1.5C range all day.

Fig. 15:  Rain at Proserpine

rain proserpine

Steady rain all day, fairly typical of cyclonic conditions.  At Strathdickie not far from Proserpine, 193mm fell in one hour that morning, and at Dalrymple Heights about 50km south 814mm fell in 24 hours.

Fig. 16:  Wind gusts at Bowen

wind bowen

For four and a half hours wind gusts reached Category 2 strength, and were above 100 km/hr from 9.00 a.m. to 8.00 p.m.

Fig. 17:  Pressure at Bowen

pressure bowen

Pressure was at Category 2 levels from 9.00 a.m.

Fig. 18:  Air temperature at Bowen

T bowen

Winds were west south west most of the day, but as Debbie passed and winds turned northwest (over the ocean), the temperature climbed.

Fig. 19:  Rain at Bowen

rain bowen

Steady rain all day: 12 inches in 12 hours.

While no stations were directly in the cyclone’s path, nearby station data indicate that Debbie was a large Category 3 to Category 4 tropical cyclone when it hit the coast and brought very strong winds, very heavy rainfall, and widespread destruction.  It is still lingering as a tropical low 300 km inland, bringing more strong winds and very heavy rain, and will head south over the next couple of days.  The clean up begins.  We await the report from James Cook University engineers who will provide their assessment of damage and wind loadings in a few weeks’ time.

Give credit where credit is due: the Bureau of Meteorology got this one pretty right.

Heatwaves: From One Extreme To Another

August 8, 2015

When Is A Heatwave Not A Heatwave?

When the Bureau of Meteorology defines it out of existence.

In his reply to me on behalf of Dr Vertessy, Bob Baldwin wrote:

“The Bureau has adopted a particular operational heatwave definition motivated by human health considerations, defined as a period of at least three days where the combined effect of high temperatures and excess heat is unusual within the local climate.  ……….The bulk of heatwaves at each location are low intensity with local communities expected to have adequate adaptation strategies for this level of thermal stress.  Less frequent, higher intensity heatwaves are classified as severe and will challenge some adaptation strategies, especially for vulnerable sectors such as the aged or the chronically ill.”

After some digging, I found this paper which describes the Bureau’s methodology used in their Pilot Heatwave Forecast:

The Excess Heat Factor: A Metric for Heatwave Intensity and Its Use in Classifying Heatwave Severity, John R. Nairn and Robert J. B. Fawcett (2015)

The method is quite easy to follow and implement, and I was able to replicate results for the 2014 Melbourne heatwave exactly and use it successfully for other single locations.   It is designed for use with AWAP gridded data of course to give forecast maps.  Note this is raw data, not homogenised.  I downloaded all data from Climate Data Online.

There are several steps.  Readers should read the paper for full details.  Briefly, using a daily mean temperature calculated by averaging the day’s maximum and the following night’s minimum, three-day means are calculated.  These are then compared by subtracting the previous 30 days’ daily means (as people acclimatise to changed temperatures in this period).  Differences that exceed the 95th percentile of all three-day means from 1971 to 2000 are multiplied by the three-day mean to give the Excess Heat Factor, which indicates heatwave.  This is then compared with the 85th percentile of all positive EHFs from 1958 to 2011 to give a severity index, and if it exceeds 3 times the 85th percentile this becomes an extreme heatwave event.

From the paper:

The intent of these definitions is to create a heatwave intensity index and classification scheme which is relative to the local climate. Such an approach is clearly necessary given the abundant evidence that people and supporting infrastructure are largely adapted to the local climate, in physiology, culture and engineered supporting infrastructure.”

Here are the results for Melbourne- with all its UHI effect of course.

Fig. 1: Decadal (running 3653 day) count of positive Excess Heat Factor (heatwave) days in Melbourne

Decadal cnt pos EHF days Melbourne

Fig.2: Decadal count of Severe Heatwave Days

Decadal cnt severe HW days Melbourne

Fig.3:  Decadal Count of Extreme Heatwave Days

Decadal cnt extreme HW days Melbourne

Notice how Melbourne heatwaves of all types have been increasing and extreme events are currently at the highest level “ever”.

How does this apply to various other Australian locations?  I decided to check with the extremes- the hottest and the coldest Australian locations, Marble Bar in the north west of W.A. and Mawson Base in Australia’s Antarctic Territory.

Fig. 4:

Map

The old Marble Bar station closed in 2006.  I have concatenated the old Marble Bar data with the new, from 2003. This makes very little difference to the calculations but extends the record to the present.

Fig. 5: As for Melbourne, decadal count of heatwave days

pos EHF days marble bar 2

Fig. 6:  Severe heatwaves

count severe HW days marble bar 2

Fig. 7:

count  extreme HW days marble bar 2

It is clear that local climate does make a big difference to heatwaves by this definition.  In fact, Melbourne has more extreme heatwave days than Marble Bar!

How does this method of detecting and measuring heatwaves deal with Marble Bar’s record heatwave of 1923-24?

According to the Australian Government’s website, Disaster Resilience Education for Schools at

https://schools.aemi.edu.au/heatwave/real-life-heatwave-stories

“Marble Bar in Western Australia holds the record for the longest number of hot days in a row: the temperature was above 37.8°C for 160 days in 1923-24.”

I count 158 days consecutively from daily data at Climate Data Online.  The total for the 1923-24 summer from 13 October to 19 April was 174 days.  That is indeed a long period of very hot weather.

Surprisingly, the BOM does not class that as a long or extreme heatwave.  Apparently, according to this metric, there were only four short heatwaves, one of them severe, and none extreme.  For the entire period, there was only one severe heatwave day – 3 February.

Fig. 8:  Marble Bar 1923-24 summer.  I have marked in the old “ton”, 100 F, or 37.8C.  Squint hard to see the “severe’ heatwave around 3 February, but the heatwave around 22 February is invisible to the naked eye.

EHF Marb Bar 1923 1924 2

Yes, the old timers at Marble Bar were pretty tough and would be used to hot conditions.  But not to recognise this old record heatwave when every day in over five months was considerably above body temperature is laughable.

For comparison, Figure 9 shows 182 day counts of days that were over 100 degrees Fahrenheit, or 37.8 degrees Celsius.  (The old record finishes in 2006.)

Fig. 9:  Running 182 day counts of days over 100 F.  1923-24 is circled.

Days 100F Marb Bar

Note there were two other years when there were more than 170 days over 100F.

Figure 10 is from Figure 16 in the Nairn and Fawcett paper, and is a map of the level of Excess Heat Factor across Australia during the heatwave of January-February 2009.

Fig. 10:  Figure 16 from Nairn and Fawcett (2014)- Excess Heat levels across Australia 21 January – 11 February 2009.

Fig16 from paper max ehf 2009

The area around Marble Bar has a level of between 0 and 10.  My calculations show this is correct- EHF reached 0.08 on 23 January- a mild heatwave.  Readers may be interested to know that maximum temperature was above 40 degrees Celsius from 1 January to 24 January, and minima were not below 24.3.

The authors, and their employer, the Bureau, are in effect telling Marble Bar locals their heatwaves don’t rate because they’re used to the heat.

Now I shall turn to the other extreme- Mawson.

Firstly, plots of the range of minima for each day of the year:

Fig. 11:  Scatterplot of minima for each day of the year at Mawson Base

minima v day Mawson

Fig. 12: maxima:

maxima v day Mawson

Fig. 13:  Decadal count (running 3653 day count) of days with positive Excess Heat Factor, i.e., by definition, heatwave days

Decadal cnt pos EHF days Mawson

Fig. 14:  Decadal count of days in severe heatwave:

Decadal cnt severe HW days Mawson

Fig. 15:  Decadal count of days in Extreme heatwave:

Decadal cnt extreme HW days Mawson

Apparently, Antarctica gets more extreme heatwave days than Melbourne, or Marble Bar!

Of course, critics will say this metric was never intended for use in Antarctica, and I agree: no one would seriously claim there are heatwaves there.  However, if heatwaves are to be defined as “a period of at least three days where the combined effect of high temperatures and excess heat is unusual within the local climate”, and NOT by comparison with any absolute threshold, then this analysis of its use there is valid.  “High” temperature by this definition is relative to the local climate, wherever “local” is. If this metric fails in Antarctica, it fails everywhere.

Conclusion:

The Bureau of Meteorology’s metric for heatwaves is a joke.  It may accurately detect heatwaves in the southern fringe of Australia, and a further use may be to support Dr Vertessy’s outlandish claims.  However, it fails to cope with different climates, particularly extremes.  A methodology that fails to detect heatwaves at Marble Bar, and creates them in Antarctica, is worse than useless- it is dangerous.

An “Eye Witness” Account of TC Marcia

February 28, 2015

A week after the event, now that our power has been restored, internet seems back to normal, and our cleanup is mostly complete, I can turn to an analysis of Tropical Cyclone Marcia.  Much initial analysis has been done, especially by Jen Marohasy at http://jennifermarohasy.com/jenns-blog/  who was in contact with me soon after the cyclone, and also by the Cyclone Testing Station of James Cook University.

However, perhaps I can add to the discussion with some additional suggestions and some personal observations.  I was there.  The eye passed over our house for about 25 to 30 minutes.  I have felt the impact in Rockhampton, experienced the electricity supply loss for 6 days and 6 hours, and cleaned up tree damage to our own 1.5 acre block, the local Heritage Village and a nursing home where a family member is resident.  Close family members were also without power.  I can also relate the experience to previous cyclones when I lived in the Mackay area.

Tropical Cyclone Marcia was a very small, intense, and short lived Complex Cyclone, with maximum winds about 30 – 40 km away from the centre, and well outside the eye wall.  At all times the Bureau of Meteorology was reporting its strength as at least one Category (more likely two) above what ground observations showed.  There is no surface evidence to show it was ever Category 5.  The only surface observation available indicates Category 3.

I watched on various websites the approach of TC Marcia throughout the day on Thursday 19th, and every couple of hours that night (few people got much sleep), and for as long as I had landline and then mobile internet connection (and power in my laptop) on Friday 20th.

Marcia rapidly intensified during Thursday.  By 5.30pm it was near Creal Reef and about 175 km  northeast of Mackay with a clearly visible eye on weather radar.

marci 17301902

The Tropical Cyclone Technical Bulletin reported it as having central pressure 958 hPa, 10 minute winds of 155 kmh and gusts to 220 kmh.  By 10.22pm it had central pressure 940hPa, winds 195 kmh with gusts to 270 kmh, and had slowed to 7 kmh but heading southwest, straight for Mackay.

By 3.20 am on Friday it was just to the east of the Percy Islands, where Middle Percy Island recorded winds from the south at 145 kmh gusting to 180 kmh.  The maximum winds here were reached between 4.00 and 4.30 am when winds reached 156 kmh gusting to 208 kmh.  Central pressure was 971.6 hPa.  It is interesting to note that the apparent temperature was 1.3 degrees C- it is very cold in a cyclone if exposed to the wind.

marci 03002002

Strongest winds and heaviest rainfall are usually in the eyewall.  Notice that the heaviest rain in the above image (yellow) is to the west of the eye- in the vicinity of Middle Percy Island.  This is what made me strongly doubt the forecast strength.  The Technical Bulletin reported it as having central pressure 929 hPa, winds 205 kmh gusting to 285 kmh, moving south at 13 kmh- straight towards Rockhampton.

The next image is from 6.00 am, about two hours before landfall, travelling south at 30 kmh.

 marci 06000220

Again note the heaviest rain outside and to the west of the eye wall.  The eye is about 25 km across.

Here is an interesting model of winds around Marcia when close to crossing the coast at 7.00 am on http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=143.66,-20.38,1821.

 winds 07002002

Strongest winds are shaded red.  Interestingly, they are to the northwest and northeast of the eye.  (Note also the deep trough from the Sunshine Coast to the border.)

After this I was busily checking final preparations, having breakfast, and making and receiving phone calls, as well as watching the websites.  By 10.00 am the wind was becoming much stronger, and the Bureau was still saying it was Cat 5 and heading straight for Rocky.

marcia forecast 10000220

Here is the radar image:

marci 10100220

Note the yellow area of heavy rain (and presumably strongest winds) south of Samuel Hill and close to Byfield.

The wind strengthened and was at its strongest by about 12.30 pm, consistently from the east.  There was one final prolonged gust, the strongest, at about 12.35 and then from about 12.50 the wind died away to nothing by 12.55 pm.  Like many others I went outside and had a look around, but didn’t go far.  It was raining lightly, heavily overcast, with puffs of wind from different directions.  At 1.25 pm we could hear the wind coming, and it picked up again over about five minutes, blowing directly from the west, but didn’t reach the same strength as before.  At a speed of 22 kmh, the eye was about 11 km across at this stage.  This screenshot shows the eye right over us at about 1.10 pm.

marci 12500220

The eye is just visible, and strongest rain and winds are to the south and east.

But this one shows it just 10 minutes later:

 marci 13000220 eye collapse

Note the eye has disappeared- it collapsed while over us.

Rockhampton Airport is about 12km south-southwest, so 30 minutes later the eye should have reached there.  But it didn’t.  Here is a screenshot of observations at Rocky Aero from 12.41 to 4.30 pm.

rocky eye

I have circled key information.  At 12.50 pm the wind was ESE at 72 kmh, with a gust to 113 kmh.  Between 1.13 and 1.52 (arrowed) the wind swung from SE to WSW, but never dropped below 24 kmh.  Lowest pressure was 975.7 hPa.  The wind steadily picked up and was strongest around 2.45 to 3.00 pm, reaching 82 kmh with a gust to 113 kmh.  This was different from my experience, where the wind was consistently from the east, then very light and variable, then directly from the west, but not as a strong.  The eye had collapsed before the centre was near the airport, and the remnants passed a couple of kilometres to the east.  The cyclone was rapidly degrading.

My last screenshot before the internet died and my battery went flat, shows the BOM forecast at 2.12pm:

marci forecast 14120220

It shows Marcia still Cat 3 at 2.00 pm.  But Rocky Aero data show winds were no more than Category 1 at this time.  At our place, the winds at this time were from the west and still damaging trees but not nearly as strong as before the eye passed.  By 3.00pm the winds were light and we were out in the street talking with the neighbours.

On eastern slopes or hills, and closer to the coast, winds would have been much higher.  I estimate gusts at our place, funnelled up a gully on an east facing slope, were around 120 – 130 kmh- similar to our experience of TC Ului at Sarina some years ago.

The Cyclone Testing Station of James Cook University has released a preliminary report at https://www.dropbox.com/s/9y8hdb74ycgemfi/TC%20Marcia%20Rapid%20Assessment%20Report%2020_02_2015.pdf?dl=0 .  They will produce more definitive analysis in a few weeks.

To summarise, this report states Yeppoon experienced Category 2 winds, and Rockhampton Category 1.  The report goes on to state:

“A community that receives an over-represented wind speed report may have potential for complacency in preparation or building standards in the future. Further research is required to determine if this is an issue.”

But was TC Marcia a Complex Cyclone, one in which maximum winds are concentrated away from the eye?  All radar images show heaviest rain, and therefore probably winds, away from the eye wall.

Byfield community is 30 km northwest of Yeppoon, half way between Yeppoon and Samuel Hill.  There are reports of every tree stripped for kilometres, which appears to indicate strong Cat 3 to Cat 4 winds.  Radar image at 10.10 am shows heaviest rain just to the west of Byfield and just to the south of Samuel Hill.  Yet Samuel Hill did not experience winds of this strength.

And here’s a photo of part of our block taken at 3.30 on the afternoon Marcia passed.

OLYMPUS DIGITAL CAMERA

Note every tree has at least 50% of its leaves stripped and several branches off, and several were completely uprooted, and these are tough old ironbarks.  So allowing for 30 km closer to the sea and two hours earlier, I wouldn’t be surprised if winds were 150 – 160 kmh at Byfield- but not 200 kmh.

Until JCU can do their complete assessment, we will not know exactly what happened.  No doubt their engineers will also visit Stanage Bay, where Marcia crossed the coast.  Tropical Cyclone Marcia was a very small, intense, and short lived Complex Cyclone, with maximum winds about 30 – 40 km away from the centre, and well outside the eye wall.  At no time was it Category 5.  Despite its relative weakness compared to some other cyclones, Marcia did tremendous damage in Central Queensland.

The main thing is no one was hurt.

Rain, clouds, and temperature

November 19, 2014

Looking at the continent of Australia as a whole, and using 12 month running means to smooth the very noisy data, we can see some intriguing patterns.

Firstly, here is a comparison of tropospheric temperatures above Australia from the University of Alabama- Huntsville (UAH), with surface air temperatures from the Bureau of Meteorology’s ACORN-SAT database.   To be comparable, both datasets are in anomalies from their 1981 – 2010 means.  The data are monthly since December 1978, with a 12 month running mean.

Fig. 1

uah v mean

Both datasets show concurrent rises and falls and are very similar (though not always).  Note how Acorn means were very much cooler in 2011 -2012 and much hotter in 2013.  Note also that 2014 has Buckley’s of being the hottest year on record.

Mean equals the average of maximum and minimum, so let’s look at maxima and minima.

Fig. 2

uah v max & min

Note that UAH usually tracks Acorn maxima, except when it doesn’t- shown above by the Xes.

Perhaps it has something to do with rainfall, or lack of it.  In the next plot, rainfall is inverted, so dry is at the top, wet at the bottom.

Fig. 3

uah v rain inv

Incidentally, the Bureau also has 9 a.m. and 3 p.m. cloud data available.  Note how closely both cloud datasets match, and how rainfall largely corresponds.

Fig. 4

rain v cloud

And the Southern Oscillation Index runs in close partnership with rainfall- sometimes SOI leads rain, sometimes rain leads SOI.

Fig. 5

rain v soi

Which is why I don’t take a lot of notice of predictions based on SOI.

Now see what happens when we plot inverted rainfall (dry at the top, wet at the bottom) and maxima.

Fig. 6

rain v max

Only once does 12 month mean maximum temperature precede 12 month rainfall (1991-1992).  At all other times, rainfall peaks or troughs occur before maxima (or at most, simultaneously).

With minima, the lead is even more obvious, however there are apparent exceptions in 1982 and 1994-1995, although these may be further examples of rain leading minima by more than a year (marked with “?”).

Fig. 7

rain v min

When we compare maxima with minima, the pattern is clear.

Fig. 8

max v min

Only in the summer of 1994-1995 do the records diverge.

Generalisations (and farmers have known about these rules of thumb for years):

  1. Climate is cyclical.  Rain and temperature rise and fall in roughly two or three year cycles.
  2. It always rains after a drought.
  3. Dry years are followed by spikes in maximum and minimum temperatures, from one to several months later.
  4. Wet years, with heavy cloud and rain, cause sharp drops in minimum and maximum temperatures, from one to several months later.
  5. Maximum temperatures lead minimum temperatures by several months in wet years, and by a shorter period in dry years.
  6. There are exceptions to all of the above.

Next step: Australia is a large continent with several distinct climatic regions.  I will next look at smaller regions to see if the above generalisations hold true and indeed may be modified or enhanced.

IPCC Dud Rainfall Predictions for the Murray-Darling Basin

April 4, 2014

The IPCC’s recently released 5th Assessment Report (AR5) dedicated Chapter 25 to impacts of climate change on Australasia. There was wide media reporting of these impacts, including that of decreasing rainfall- more droughts and floods. The relevant part of Chapter 25 outlines eight regional key risks, including:

For some impacts, severity depends on changes in climate variables that span a particularly large range, even for a given global temperature change. The most severe changes would present major challenges if realized:

……. significant reduction in agricultural production in the Murray-Darling Basin and far south-eastern and south-western Australia if scenarios of severe drying are realised; more efficient water use, allocation and trading would increase the resilience of systems in the near term but cannot prevent significant reductions in agricultural production and severe consequences for ecosystems and some rural communities at the dry end of the projected changes.

Section 25.2, Observed and Projected Climate Change, gives the details:

This pattern of projected rainfall change is reflected in annual average CMIP5 model results (Figure 25-1), but with important additional dimensions relating to seasonal changes and spread across models (seealso WGI Atlas, AI.70-71). Examples of the magnitude of projected annual change from 1990 to 2090 (percent model mean change +/- intermodel standard deviation) under RCP8.5 from CMIP5 are -20±13% in south-western Australia, -2±21% in the Murray Darling Basin, and -5±22% in southeast Queensland (Irving et al., 2012). Projected changes during winter and spring are more pronounced and/or consistent across models than the annual changes, e.g. drying in southwestern Australia (-32±11%, June to August), the Murray Darling Basin (-16±22%, June to August), and southeast Queensland (-15±26%, September to November), whereas there are increases of 15% or more in the west and south of the South Island of New Zealand (Irving et al., 2012). Downscaled CMIP3 model projections for New Zealand indicate a stronger drying pattern in the south-east of the South Island and eastern and northern regions of the North Island in winter and spring (Reisinger et al., 2010) than seen in the raw CMIP5 data; based on similar broader scale changes this pattern is expected to hold once CMIP5 data are also downscaled (Irving et al., 2012).

As the Murray-Darling Basin (MDB) is the nation’s major food bowl, contributing a very large proportion of our agricultural production, a Reality Check on these claims is in order.

The Murray-Darling Basin is the largest catchment in Australia, and is one of the Bureau of Meteorology’s climate regions:

Fig.1: MDBRegions

First, annual rainfall. The IPCC projects an annual change of -2% +/-16% from 1990 to 2090. Here are the rainfall anomalies for the MDB straight from the Bureau’s Climate Change page:

Fig.2: MDB Annual Rainfall Anomalies, 1900-2013:MDB annual anoms

Linear trends have limited use in such a manifestly non-linear dataset as rainfall, however I put one in just in case someone says rainfall is decreasing. Even with 2010 deleted the trend is still positive. Let’s now look at the 10 year means:

Fig.3: MDB Annual Decadal Means:MDB annual anoms 10yrs

Note that for the entire period before the 1950s, the 10 year mean was below the 1961-1990 mean, and in 1946 was 94mm below. While in 2009 the 10 year average was 69mm below the mean, this being the first time in six decades it had been below -60mm, for most of the 1940s it was more than 60mm below the mean. It is entirely possible that rainfall will be below average in the MDB for several more decades, and this would be completely normal.

I shall now project this historical trend through to 2090, with a 2090 rainfall of 512.35mm, 2% below that of 1990 (522.81mm).

Fig.4: MDB Annual Rain to 2090:MDB annual rain to 2090

So that’s what a decrease in rainfall looks like! Note the uncertainty range- well within historical norms, and the low figure (404.76mm) is in the below average (lowest 30% of years) rainfall category by less than 4mm.

Next, winter rainfall (-16% +/-22%, June to August). From BOM Climate Change,

Fig.5: MDB Winter Anomalies 1900-2013MDB winter anoms
There you can see the declining trend (BOM says -0.57mm per decade)- but note the size of the trend compared with the variability.

Interestingly, consider the same data for the last 54 years.

Fig.6: MDB Winter Anomalies 1960-2013MDB winter anoms 1960-2013
But of course, the authors have detected the drying trend since the 1990s!

Now, decadal means:

Fig.7: MDB winter decadal means:MDB winter anoms 10yrs

Note the 10 year mean about -10mm in past decade, but -15mm in the 1970s and -19mm in the 1940s. Note also that the 10 year average was below zero for the better part of two decades, twice, in the past. Below average winter rain for the next few years would be completely normal, if the past is anything to go by.

Here is a chart showing the number of dry winters per 10 year period in the MDB.

Fig.8: 10 year count of below average winters.MDB winter anoms  under30%10yrs

Below average winters were more frequent in the past.

Projecting the winter anomalies into the future, with a decrease of -16±22%, June to August, we get:

Fig.9: MDB Winter Rain to 2090:MDB winter rain to 2090

109.74mm is almost exactly the 1961-1990 mean (111.1mm). The low end of the uncertainties, 85.6mm, is in the below average range but well outside the severe deficiency or even serious deficiency level. Yet this will cause “significant reductions in agricultural production and severe consequences for ecosystems and some rural communities”?

Note: these projections are based on continued warming by up to 2 degrees. Consider that we have already seen warming in the MDB of about +0.8 C since 1910 (according to BOM analysis based on ACORN-SAT).

It appears that the IPCC can’t be wrong, whether rainfall is higher, lower, or stays the same. They’re having two bob each way.

In discussing agricultural production, I would have been less underwhelmed if rainfall in other seasons had been considered. If winter rain is down (marginally), but annual rain is up, when did it fall?
Briefly, autumn, like winter, is almost flat (-0.59mm per decade), spring is up by 1.61mm per decade, but summer rain has increased 3.86mm per decade. If heavy rain falls before the wheat harvest is off, the crop is seriously downgraded, so late spring- early summer rainfall increasing would be of concern.

Fig.10: MDB Summer Rain AnomaliesMDB summer anoms

Fig.11: MDB Decadal Summer RainMDB summer anoms 10yrs

Note that summer rain increase is all since 1950. For 60 years farmers have been contending with this. It’s nothing new. Farmers adapt farming methods to changing conditions and with new technology. Moreover, the recent decadal peak is about the same as the 1960s and 1990s. Note also that the low decadal mean of the Millennium Drought is nowhere near the levels of past dry periods.

The warming to now has ‘resulted’ in increased annual rain, made up mostly of stronger summer rains since 1950, and marginally less winter and autumn rain which is less variable than in the early decades of last century.  The IPCC’s projections are thus the result of climate models and not historic observation, are subject to large uncertainty, and not greatly different from patterns of the past 114 years.

The AR5 prediction of dire consequences for the Murray-Darling Basin, based on rainfall projections that are essentially no different from historical observations, is nonsense. It is beyond parody, beyond ridicule. It treats the citizens and farmers of Australia with contempt.

What did Chris Turney expect?

January 5, 2014

Professor Turney did not have to take an unsuitable ship full of “climate tourists” to Antarctica.  He could have just checked the Bureau of Meteorology’s website.

As the Aurora Australis will be calling at Casey base to deliver delayed supplies before returning the hapless Turney and the rest of the expedition to Australia, I thought I’d help with what conditions to expect at Casey.  I used official ACORN-SAT monthly data to 2011 and Climate Data Online daily temperatures since then.

Here are the actual monthly maximum temperatures at Casey for 2013:Casey max 2013

As you can see, temperatures were below the mean (calculated from 1970-1990) for most of the year, and the monthly mean maximum temperatures were above freezing (the straight blue line) only in January and December.  Monthly mean minimum temperatures never get above freezing.   (The highest daily minimum in 2013 was +1.7 C on 15 January.  The warmest minima this summer were on 29 and 30 December.  It got to +0.3.)

And has there been recent warming?

This graph is of maximum and minimum anomalies from the 1970-1990 means, smoothed with running 12 month means:Casey 1970-2013

Australia has three bases on the Antarctic coast, Casey, Davis, and Mawson.  Davis and Mawson show some slight warming:Davis 1958-2013Mawson 1958-2013

The mean anomalies of all three sites:Antarctic means

show a linear trend of about  +0.15 C- but the rise (such as it is)  is by no means steady.

To show how insignificant the warming is in Antarctica, here are annual mean anomalies compared with those of Australia:Antarctic-Oz comp

Remember, one of the so-called “fingerprints of greenhouse warming” is that warming should be greater towards the poles.

Professor Turney could have saved himself a lot of time, trouble, and embarrassment.

BOM’s Annual Climate Statement

January 3, 2014

This is just a quick comment on the 2013 Annual Climate Statement released today by the Bureau.

I have checked only minimum temperatures, and my calculation I released yesterday for the 2013 annual mean for minima was +0.82 C.  The Bureau has reported  an annual average of +0.94 C.

The BOM’s figures are derived from the Acorn dataset.  They acknowledge in the small print that:

Note that all values in this statement are as compiled from data available on 2 January 2014. Subsequent quality control and the availability of additional data may result in minor changes to final values.

What they really mean is that Acorn won’t be updated with 2013 data for several weeks, and that nearly all Acorn sites have many months of daily data that has not yet been quality controlled.  This means that the values they give can not be checked for several weeks.

As well, three Acorn sites in Western Australia ceased reporting in August 2012.  Bridgetown has years of data that is out by two days, and Rutherglen has years of data out by one day.   And on some 800 occasions the minimum temperature is higher than the maximum.  Quality checking is not as rigorous as you might expect.

Any changes may be only minor, but rushing to publish before the data can be checked is not a good look.

Weather predictions- final check

January 3, 2014

This is the final post in my series of checking a hunch that temperature change indicates a weather change 160 days later.

Back on November 3, I predicted:

“December
2 to 10 unstable; 12-13-14; 16-17-18-19; 22-23-24; 26 to 31 unstable.”

I did not change this in December.

This is how  I went:

Dec2013 predictions check

I’ve marked with green bars the predicted dates of unsettled weather as above.  Red bars show the actual times.  They match.

And finally, here’s my graph showing predicted weather events for April to June.  Again, green bars indicate dates when weather events may be expected.Apr-June 2014

I will leave this topic for now, not because the method doesn’t work (it does!), but to concentrate on other interests.

Weather predictions: December

December 1, 2013

At the start of November, I said:

“November
5 to 10 unstable; 13 to 21 unstable with several events; 26-27-28-29-30 unstable.”

All correct, 1 miss.  Instability with some very wild storms marked much of November especially in the South-East of the state.

Now I suppose anyone could have predicted storms for November.  But remember, back in August I had said:

“November

5-6-7, 9-10, 13-14-15, 17-18-19-20, 27-28-29.”

Here’s a chart showing August predictions in light green and early November predictions in dark green.octdec13resultsnov

5 right, I miss.  I should have stuck with my original predictions!

So the method is holding.

Predictions for December to 31 March remain the same as I predicted last month.  As well, I expect weather events around these dates in April and May (+/- 1 day):

2,4,7,11,15,20,23,25, May 1, 8,11.

April should have unstable weather, and I would not be surprised if we get significant rain.

 

Weather Predictions November – March

November 3, 2013

At the start of October, I made the following predictions:

October
Sep 30- 1-2, 8-9-10, 14-15-16, 20-21-22-23, 25?, 28-29-30-31-Nov 1 (possibly 2 events).

Changes were detected on:- 2-3, 8-9, 13-14, 17-18, 22-23- 24, 28- 29-30-31 (the”possibly 2 events” was true indeed with a series of storm fronts that persisted.)Oct 13 results & pred

Dark red is Tmin, pink is Tmax, black is inverted pressure, blue is rain, green is the 160 day lagged Tmin, yellow is 40 day lagged pressure.  I may try 40 day lagged temperature in future.   November and December predictions are shown as red ovals.  So there were 5 correct predictions, 1 wrong, and 1 miss (although the wrong event would have been a “correct” if it had been a day earlier).  Not bad for 160 days out, I console myself.  I also suspect there has been a slight acceleration of weather systems, so perhaps I should be looking at events around 158 days ahead instead of 160.  No matter for now but I will keep an eye on it.

Predictions for November and December (slightly adjusted from last month):

November
5 to 10 unstable; 13 to 21 unstable with several events; 26-27-28-29-30 unstable.
December
2 to 10 unstable; 12-13-14; 16-17-18-19; 22-23-24; 26 to 31 unstable.

 January to March:

Here is the graph I use for predicting weather changes, which shows 2nd derivative, or acceleration/deceleration, of minimum temperature.

jan-mar 2014 predictions

Think of a cool change moving through from the west.  A large temperature differential, or a fast moving change, both have the same effect.  When the green line goes below zero, the temperature has decelerated, and a change (or unsettled weather) occurs in the time period indicated.  Several rapid oscillations appear to relate to unsettled weather.  My only problem is I am averaging over a very wide region, and the time lag may be changing.

There is always something to learn.