Archive for the ‘Rainfall’ Category

Drought and Climate Change Part 2: Rainfall deficiency

September 7, 2018

In my last post, I looked at long term rainfall trends across Southern, South Eastern, and South Western Australia, and found no cause for alarm at recent rainfall decline.  Droughts can occur at any time and cause much hardship across wide parts of the country.  Global Warming Enthusiasts are gnashing their teeth, believing man-made climate change is making droughts worse.  Greg Jericho in the Guardian wrote last Thursday 30th August, “If you are a prime minister going out to the rural areas and you’re not talking about climate change, and you’re not suggesting that droughts are more likely to occur and thus farmers need to take greater responsibility, then you are failing in your job.”

Are droughts really “more likely to occur” with climate change, and is there any evidence they are becoming more frequent, more intense, and more widespread with global warming?

The Bureau of Meteorology says:

Drought in general means acute water shortage.

The Bureau’s drought maps highlight areas considered to be suffering from a serious or severe rainfall deficiency…. for three months or more….

……

  • 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.”

This map of meteorological drought (areas in the lowest ten and five percent of 12 months rainfall to 31 August) shows the extent across Australia:

Fig. 1:  Recent 12 month Rainfall Deficiency Australia

12m drought map

Parts of central and southern inland Queensland, parts of eastern South Australia, many parts of New South Wales, and small areas of Victoria are in drought.  Notice that the droughted areas are separated by areas that are not in drought.

But, but… all of NSW is in drought, isn’t it?

100% of NSW has been drought declared, and 54.7% of Queensland, and indeed some parts are in a very bad way.   But “drought declaration” is the term the media, politicians, and general public don’t understand.  They assume that because 100% of NSW is drought declared, this means all of NSW is in drought.  Not so.  Drought declaration is a political or at best administrative instrument for giving drought assistance to farmers and communities.  Some areas of Queensland that have not yet been drought declared really are in the grip of drought; some “drought declared” areas of NSW are not in drought, as this map of NSW (6 months March to August) shows:

Fig. 2: 6 month Rainfall deficiency NSW

NSW map 6m

Of course the blank areas have had below average rainfall, which may turn into full blown drought, so the NSW government is being proactive.  However, they are not at this time in meteorological drought with serious or severe rainfall deficiency.

Trends in Drought Incidence

In the bigger picture, how widespread, how intense, how long lasting, and how frequent are droughts becoming in Australia?  For this analysis I use monthly rainfall data from 1900 to July 2018 from the Bureau of Meteorology at their Climate Change page, and calculate the number of months where the rainfall total of the previous 12, 18, 24, or 36 months shows severe deficiency (in the lowest 5 percent of all months since 1900) or serious deficiency (in the lowest 10 percent).  (I am looking at droughts that last at least 12 months, not just short dry spells, and 12 months total rainfall includes rain in all seasons.)

I do this for various regions, as shown on the map below.

Fig. 3:  Australian Regions

Climate regions

I have plotted the number of consecutive months where the 12, 18, 24, and 36 month totals are in the lowest 5% and 10% of their respective values since 1900, and calculated the trend in months per century of increase or decrease. There are 96 plots, so I will only show a couple of examples, and summarise the results in Table 1 below.

Table 1:  Trends in Drought Incidence (Months per 100 Years) for various Australian Regions

Trend table

A negative trend indicates decreasing drought incidence, shaded green; a positive trend indicates increasing incidence, shaded pink.

Australia wide, and in the regions of Northern and Southern Australia and the Murray Darling Basin, and South Australia as a whole, since 1900 droughts of all lengths have become less frequent, and because these are broad regions, less widespread.  There is no evidence that climate change is making droughts more likely to occur, except for smaller areas (Victoria, Tasmania, and SW Australia) which have an increasing frequency of droughts of all lengths.

36 month dry periods are more frequent in SW Australia, SE Australia, Eastern Australia, Tasmania, Victoria, (and interestingly Queensland, but only for <10% deficiency).

Some examples will illustrate the complexity of the picture.

Fig. 4:  Number of consecutive months per calendar year of 12 months severe rain deficiency: Australia

12m 5% Aust

Fig. 5:  Periods of 36 months serious rain deficiency: Australia

36m 10% Aust

In the past droughts of all lengths and severity were more widespread across Australia.

Fig. 6:  Periods of 36 months severe rain deficiency: Southern Australia

36m 5% Sthn Aust

Similarly, multi-year periods of severe rain deficiency were much more frequent and widespread across Southern Australia before 1950.  In the last 50 years there has been only one month where the 36 month total was in the lowest 5th percentile.

Fig. 7:  Periods of 12 months severe rain deficiency: New South Wales

12m 5% NSW

Fig. 8:  Periods of 36 months severe rain deficiency: New South Wales

36m 5% NSW

Fig. 9:  Periods of 12 months serious rain deficiency: New South Wales

12m 10% MDB

Fig. 10:  Periods of 36 months serious rain deficiency: New South Wales

36m 10% NSW

Across NSW, 4 months of 2018 had 12 month totals in the serious deficiency range, but none in the severe range.  Droughts of all severity and duration have become less frequent and widespread.  The Millennium Drought lasted longer but was less severe than the Federation Drought.

The Murray-Darling Basin lies across four states including most of NSW, and is Australia’s premier food and fibre producing region.  The current drought is affecting many areas in this region.

Fig. 10:  Periods of 12 months severe rain deficiency: Murray-Darling Basin

12m 5% MDB

Fig. 11:  Periods of 12 months serious rain deficiency: Murray-Darling Basin

12m 10% MDB

Fig. 12:  Periods of 36 months serious rain deficiency: Murray-Darling Basin

36m 10% MDB

We can conclude from these plots of the Murray-Darling Basin that this drought is patchy, and while nasty, is not the most intense or long lasting even in living memory, let alone on record, and that droughts are becoming less frequent and less widespread.

Fig. 13:  Periods of 36 months severe rain deficiency: Queensland

36m 5% Qld

Fig. 14:  Periods of 36 months serious rain deficiency: Queensland

36m 10% Qld

Queensland has little trend in frequency of drought with severe deficiency over three years but less severe droughts have been more frequent- due to the droughts of the 1990s and the Millennium drought.

Fig. 15:  Periods of 36 months serious rain deficiency: Victoria

36m 10% Vic

The Millennium Drought stands out as the longest period of widespread serious rain deficiency.

Fig. 16:  Periods of 36 months serious rain deficiency: South-West Australia

36m 10% SW Oz

Here we see that all but one month of all the 36 month periods of serious rain deficiency have occurred since 1970, reflecting the marked drying trend.  This really is an example of climate changing.

Winter rainfall

Fig. 17:  Winter Rainfall Deciles across Australia, 2018

winter rain 2018

According to the Climate Council, “Climate change has contributed to a southward shift in weather systems that typically bring cool season rainfall to southern Australia.”  However the usual areas affected by this southwards shift, Tasmania, south-west Victoria, southern South Australia, and most of the south-west of Western Australia, have had an average to above average winter.  Droughted areas are to the north.   The southwards shift of weather systems caused by Climate Change cannot be claimed to have any part in this drought.

Drought is a dreadful calamity wherever and whenever it occurs.  And on top of other difficulties in Queensland is the bureaucratic approval process under Vegetation Management regulations before graziers can push mulga to feed starving stock.

This drought may get worse if a full El Nino develops.  It is unlikely to break before six months or even 18 months.  By then it will be much more severe and widespread.  However, climate change has not caused this drought.  While there is evidence for increasing drought frequency and thus likelihood of more drought in the future in Tasmania, southern Victoria, southern South Australia, and the south-west of Western Australia, across the rest of Australia there is strong evidence that droughts have become less frequent, less severe, less widespread, and shorter.  If climate change is claimed as the cause of increasing droughts in the far southern regions, then climate change must also be causing less frequent droughts across the vast bulk of Australia, where droughts are always “likely to occur”, but not “more likely”.

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Drought and Climate Change Part 1: Long Term Rainfall

September 1, 2018

The current drought conditions in New South Wales and large parts of Queensland are getting a lot of media attention, and of course the usual suspects are linking it to climate change and our apparently “unambitious” emissions targets in the NEG.  But are droughts really becoming “the new normal”, and are they becoming more frequent, more intense, and more widespread with global warming?

There are two aspects to consider: long term rainfall trends in various regions, and periods of rainfall deficiency.  In this post I will look at long term rainfall, and Part 2 will look at rainfall deficiency i.e. drought incidence.

Long term rainfall trends

Everyone “knows” southern Australia is getting drier.  Paul West in Feeding Australia Pt 2 on the ABC says there has been a 28% decrease in rainfall over the past 30 years.  The Climate Council says “Over the past 30 years, there has been a discernible decrease in rainfall across southern Australia.” That’s their headline; in the details the Climate Council’s June 2018 Fact Sheet says:

“Climate change has contributed to a southward shift in weather systems that typically bring cool season rainfall to southern Australia. Since the 1970s late autumn and early winter rainfall has decreased by 15 percent in southeast Australia, and Western Australia’s southwest region has experienced a 15 percent decline in cool season rainfall.”

Both are true, but both are only half true, and in fact the ABC and the Climate Council as usual lie by omission.

The whole story is more complex but shows a completely different, and much less dramatic picture.  Using data for cool season (April- September) rainfall from the Bureau of Meteorology we can check on different time periods.

Fig. 1:  Cool season rainfall, Southern Australia, 1988-2017

Cool rain Sth Oz 19882017

Yes, if this is what Paul West based his statement on, 2017 had about 28% less rain than in 1988.  I hope he didn’t- comparing single years would be pretty bad science.  However there has been a marked decrease in cool season rainfall over this period, so the Climate Council is quite correct.

However, Figure 2 shows the big picture- since 1900.

Fig. 2: Cool season rainfall, Southern Australia, 1900-2017

Cool rain Sth Oz 19002017

Oops! Rainfall has in fact increased over southern Australia.

The reason for the current gnashing of teeth is that “living memory” only goes back about 70 years, and we are comparing current conditions with those of a few decades ago.  Figure 3 shows the average rainfall for the 10 year periods up to 2017.

Fig. 3: 10 year average Cool season rainfall, Southern Australia, 1900-2017

Cool rain Sth Oz 19002017 10yrs

As you can see, the average rainfall of the 10 years 2008 to 2017 was about 7% less than in the 1950s, 1970s, 1980s, and 1990s, but more than the 1920s and 1930s, and nearly 10% more than the 10 years to 1947.  Of the 10 decades before this one, five had less rain and five had more.  Southern Australian cool season rainfall is not “the new normal”, it is in fact “the old normal”.

Let’s now look at South-East Australia, below 33 degrees South and east of 135 degrees East.

Fig. 4: Cool season rainfall, South-Eastern Australia, 1988-2017

Cool rain SE Oz 19882017

Again there is an obvious decrease in rain over the last 30 years.

Fig. 5: Cool season rainfall, South-Eastern Australia, 1900-2017

Cool rain SE Oz 19002017

There has been a small decrease in cool season rainfall over the whole 118 years.  Again there was a marked step up in rainfall from the mid-1940s.  The plot of 10 year averages shows this more clearly:

Fig. 6: 10 year average cool season rainfall, South-Eastern Australia, 1900-2017

Cool rain SE Oz 19002017 10yrs

There was a decreasing trend up to the 1940s, and a decreasing trend from the 1950s to now.  The current 30 to 40 year decrease is nothing new.

However, rainfall records for individual sites go back much longer.  What do these show?  Here is a plot of monthly rainfall for all months at Penola, in South Australia, starting in 1863:

Fig. 7: Monthly rainfall (all months January 1863 – December 2017) at Penola, S.A.

Penola rain monthly

A very long term decreasing trend.  Running 12 month totals show wetter and drier periods:

Fig. 8: 12 month running total rainfall (all months January 1863 – December 2017) at Penola, S.A.

Penola rain 12m

There were very severe droughts around World War 1 and the late 1960s, but a big step up in the 1950s.  This is more obvious in a plot of 10 year totals:

Fig. 8: 120 month running total rainfall (all months January 1863 – December 2017) at Penola, S.A.

Penola rain 120m

This site shows a very long term rainfall decrease, complicated by droughts and strings of wetter years, and a huge step up in the middle of last century.  This site is one of many of varying lengths in the High Quality Rainfall dataset.  Nearly all show the mid-century step up, some show a small long term increase, some show a small long term decrease.

I amalgamated all 84 stations, and here are the plots for all months. Firstly, the number of stations reporting:

Fig. 9: Count of all stations in S.E. Australia reporting, all months

All SE sites Count

There are a number of long term sites.  There were 50 sites in 1898, as in 2017 (several had not yet reported January 2018).

Note: the following plots are of naïve means: there is no area averaging.

Fig. 10: S.E. Australia monthly rainfall (all months)

SE Oz all months

Note a small increase.  Now 12 month running totals of these means:

Fig. 11:  S.E. Australia 12 month rainfall (all months)

SE Oz 12 months

Now the 10 year running total of monthly means, but since 1898 when the number of stations was the same as now:

Fig. 12:  S.E. Australia 120 month rainfall (all months)

SE Oz 120 months 1898

The mid-century step up is obvious, with a decline since then.  The 10 year rainfall to December 2017 is about what it was a century ago.

I now turn to South West Australia.

Fig. 13: Cool season rainfall, South-Western Australia, 1988-2017

Cool rain SW Oz 19882017

A very serious decline since 1988.

Fig. 14: Cool season rainfall, South-Western Australia, 1900-2017

Cool rain Sw Oz 19002017

As you can see, the decline has been around since 1900, but with a marked step down starting in 1968, with a steep but uneven decline since then.  10 year averages show this clearly.

Fig. 14: 10 year average cool season rainfall, South-Western Australia, 1900-2017

Cool rain SW Oz 19002017 10yrs

Conclusion:

The long term data show a complex picture of long term cool season rainfall decline in south-west and some parts of south-east Australia, while southern Australia as a whole shows a very small increase.  It is true that rainfall has declined, as the Climate Council and ABC claim, over the past 30 and 40 years in many parts, but that is only half the story.  The whole story is much less dramatic.  Rainfall has been declining for a long time in WA, and in south-east Australia has been declining in two stages, separated by a large step up in rainfall in the middle of last century.

The current low rainfall is not “the new normal” but entirely consistent with “the old normal” and should be seen as just plain “normal”.  This is Australia.  Get used to it.

Unprecedented South Australian Weather!

January 22, 2017

(and it has been like that for 178 years!)

There were more blackouts in South Australia a couple of days ago following a wild storm.  In a report in the Adelaide Advertiser, SA Power Networks spokesperson Paul Roberts is quoted:

“This is just another example of the unprecedented weather in the last six months,” Mr Roberts said, referring to bouts of wild weather that have hit power supplies hard this summer and the preceding spring.

21mm of rain was measured at the Kent Town gauge.

Just how “unprecedented” is Adelaide’s weather over the past few months?  I couldn’t find any records for the number of severe storms, so for a proxy I have made do with rainfall data from West Terrace and Kent Town in Adelaide.  The overlap period has very similar rainfall recordings so I joined the two series to give a record starting on 1 January 1839.  That’s 178 years of data.

When thinking about “unprecedented”, we need to check amount, intensity, and frequency.

Firstly, a few plots to give some context.  How unprecedented was Thursday’s storm?

Fig. 1: Rainfall for the first 21 days of January compared with Days 1 – 21 of every year

adelaide-rain-21-jan

Note Thursday’s rainfall had less rain than four previous occasions on this day alone, and 20 or so in previous Januarys.

Fig. 2: Rainfall for each day of 2016 compared with each day of every year:

adelaide-rain-2016

Note the December storm had extreme rain (for Adelaide) but not a record.

Amount and intensity has been higher in many previous years.  141.5mm was recorded on 7 February 1925.

Fig. 3: 7 day average rainfall over the years:

adelaide-rain-2016-7d-avg

The topmost dot shows the maximum 7 day average for each year.  2016 got to 13.4mm on 4 October- multiply by 7 to get the weekly total rain.  Note there were many wet and dry periods all through the record.

21mm of rain fell in a severe storm on Thursday, so I arbitrarily chose 20mm as my criterion for heavy rainfall in one day as a probable indicator of stormy weather.  I am the first to admit that 20mm might fall steadily all day and not be at all associated with wild winds, and wild winds can occur without any rain, but bear with me.

Fig. 4: Rain over 20mm throughout the year:

adelaide-rain-2016-above-20

There seems to be no increase in amount or intensity of rain at any time of the year.

Fig. 5: Frequency:

adelaide-rain-2016-cnt-above-20

Note 2016 had 7 days with above 20mm in 24 hours.  That’s the most since… 2000, when there were 8 days- and many previous years had 7 or 8 days, and 1889 had 9.  So no increase in frequency.

However, Mr Roberts was referring to the last six months, spring and summer.  So let’s look at rain events over 20mm from July to December, firstly amounts recorded:

Fig. 6: July to December Rain over 20mm:

adelaide-rain-above-20-last-6m

Nothing unusual about 2016.

Fig. 7:  Frequency of heavy rain July – December:

adelaide-rain-2016-cnt-above-20-last-6m

1973, 1978, and 1992 had the same or more days with over 20mm.

I now restrict the count to spring and summer only:

Fig. 8:  Spring and Summer frequency:

adelaide-rain-2016-cnt-above-20-last-4m

Not unprecedented: 1992 had one more.  Add in last Thursday’s event to make them equal.

Conclusion

Adelaide has a long climate record, showing daily rainfall has varied greatly over the years.  There is no recent increase in amount, intensity, or frequency for the whole year, or for the last six months or four months.  Spring and summer rainfall in 2016 was not unprecedented, and to the extent that spring and summer falls over 20mm are a proxy for storms, there is no evidence for an increase in wild weather.  This is normal.  Get used to it, Mr Roberts, and make sure the electricity network can cope.

 

Land and Sea Temperature: South West Australia

November 29, 2016

This year, the south-west of Western Australia has recorded some unexpectedly low temperatures.  Has this been due to rainfall, cloud, winds, or the cooler than normal Leeuwin Current and Sea Surface Temperatures in the South West Region?

In this post I examine maximum temperature and rainfall data for Winter in South-Western Australia, and Sea Surface Temperature data for the South West Region, all straight from the Bureau of Meteorology’s Climate Change time series page .

All temperature data are in degrees Celsius anomalies from the 1961-90 average.

Figure 1 is a map showing the various Sea Surface Temperature monitoring regions around Australia.

Fig. 1

sst-regions

The Southwest Region is just to the west and southwest of the Southwest climate region, and winter south westerlies impact this part of the continent first.  2016’s winter has seen maxima drop sharply.  In fact, it was the coldest winter since 1993:

Fig. 2:  Southwestern Australia Winter TMax Anomalies

sw-tmax

There is a relationship between rainfall and Tmax- as rain goes up, Tmax goes down, so here south west rainfall is inverted and scaled down by 100:

Fig. 3:  TMax and Rain:

sw-tmax-rain

The next plot shows TMax and the South West Region’s Sea Surface Temperature anomalies (SST):

Fig. 4:  TMax & SST:

sw-tmax-sst

Again, related: both have strong warming from the 1970s.  Next I check for whether there was a real change in direction in the 1970s, and if so, when.  To do this I use CuSums.

Fig. 5:  CuSums of Winter TMax and SST compared:

sw-tmax-sst-cusums

Both have a distinct change point: 1975, with SST warming since, but TMax appears to have a step up, with another change point at 1993 with strong warming since.  Rainfall however shows a different picture:

Fig. 6:  CuSums of Winter Rainfall

sw-rain-cusums

Note the major change at 1968 (a step down: see Figure 3), another at 1975 with increasing rain to the next change point at 2000, after which rain rapidly decreases.

I now plot TMax against rainfall and SST to see which has the greater influence.  First, Rain:

Fig. 7:  TMax vs Rain:

sw-tmax-vs-rain

100mm more rain is associated with about 0.5C lower TMax, but R-squared is only 0.22.

Fig. 8:  TMax vs SST:

sw-tmax-vs-sst

A one degree increase in SST is associated with more than 1.1C increase in TMax, and R-squared is above 0.51- a much closer fit, but still little better than fifty-fifty.

TMax is affected by rain, but more by SSTs.

I now look at data since the major change points in the 1975 winter.  The next three figures show trends in SST, Rain, and TMax.

Fig. 9:  Trends in SST:

sw-sst-trends

Warming since 1975 of +1.48C/ 100 years.

Fig. 10:  Trends in Rainfall:

sw-rain-trends

Decreasing since 1975 at 89mm per 100 years (and much more from 2000).

Fig. 11:  Trends in TMax:

sw-tmax-trends

Warming since 1975 at +2.14C per 100 years.

Detrending the data allows us to see where any of the winters “bucks the trend”.  In the following plots, the line at zero represents the trend as shown above.

Fig. 12:  SST Detrended:

sw-sst-detrended-75-to-16

Fig. 13:  Rainfall Detrended:

sw-rain-detrended-75-to-16

Fig. 14:  TMax Detrended:

sw-tmax-detrended-75-to-16

Note that SST in 2016 is just below trend, but still above the 1961-90 average.  Rainfall is only slightly above trend, and still below average.  However TMax is well below trend, and well below average, showing the greatest 12 month drop in temperatures of any winter since 1975.

My conclusions (and you are welcome to comment, dispute, and suggest your own):

  • Maximum temperatures in winter in Southwestern Australia are affected by rainfall, but to a much larger extent by Sea Surface Temperature of the South West Region.
  • The large decrease in winter temperature this year cannot be explained by rainfall or sea surface temperature.  Cloudiness may be a factor, but no 2016 data are publicly available.  Stronger winds blowing from further south may be responsible.

DTR, Cloud, and Rainfall

September 19, 2016

In my last brief post I showed how Diurnal Temperature Range is related to rainfall in Northern and Southern Australia in Northern and Southern wet seasons (which correspond roughly to summer and winter).

In this post I show the relationship between DTR and daytime cloud, and between rainfall and daytime cloud, and something very peculiar about South-Western Australia.

All data are taken straight from the Bureau’s Climate Change Time Series page.

DTR is affected by rainfall through Tmax being cooled by cloud albedo, evaporation and transpiration, and Tmin warmed by night cloud and humidity.  There must be a relationship between clouds and rain, although it is (rarely) possible to have rain falling from a clear sky with no visible cloud.  Rain is easily measured in standard rain gauges.  Cloud is calculated by trained observers, and we only have data for 9 a.m., 3 p.m., and daytime cloud.  The data give no indication of cloud type, thickness, or altitude, just amount of sky covered (in oktas, or eighths).

Here I show scatterplots for Australia as a whole annually, and for Northern, South-Eastern, and South-Western Australia in summer and winter.  I calculate both rainfall and cloud as percentage differences from their means.

Fig. 1:  DTR vs Rain for Australia annually:

dtr-vs-rain-oz-ann

Fig. 2:  DTR vs Cloud for Australia annually:

dtr-vs-cloud-oz-ann

Notice much better correlation between DTR and Cloud.

Now let’s look at the relationship between rainfall and daytime cloud.

Fig. 3:  Percentage difference in Rainfall vs percentage difference in Cloud for Australia annually:

rain-v-cloud-oz-ann

Note a 10% increase in cloud cover could be expected to be associated with a 25% increase in rainfall.

Fig. 4: Percentage difference in Rainfall vs percentage difference in Cloud North Australian summers:

rain-v-cloud-n-oz-summ

Fig. 5: Percentage difference in Rainfall vs percentage difference in Cloud North Australian winters:

Note how rainfall in the North Australian dry season varies proportionally more, but has a slightly lower correlation (>0.8 vs 0.9).

Fig. 6: Percentage difference in Rainfall vs percentage difference in Cloud South-East Australian summers:

rain-v-cloud-se-oz-summ

Note the much greater effect of cloud on rainfall in the southern dry season.

Fig. 7: Percentage difference in Rainfall vs percentage difference in Cloud South-East Australian winters:

rain-v-cloud-se-oz-wint

Now, get ready for a surprise.

Fig. 8: Percentage difference in Rainfall vs percentage difference in Cloud South-West Australian summers:

rain-v-cloud-sw-oz-summ

Fig. 9: Percentage difference in Rainfall vs percentage difference in Cloud South-West Australian winters:

rain-v-cloud-sw-oz-wint

What’s going on in the south-west?

Here’s how DTR compares:

Fig. 10:  DTR vs percentage difference in rainfall: South-west Australia

dtr-vs-rain-sw-oz-ann

Similar relationship to everywhere else.

Fig. 11:  DTR vs percentage difference in cloud cover: South-west Australia

dtr-vs-cloud-sw-oz-ann

And this graph clearly shows the relationship between rain and cloud is closer in the wet seasons, but also clearly shows that South-west Australia is an extreme outlier.

Fig. 12:  R-squared comparison between rain and cloud in wet and dry seasons

chart-seasonal-r2

Why the huge difference?  There is no relationship between cloud and rain in south-west Australia, unlike everywhere else.  The South-West has seen a marked decline in rainfall since the late 1960s, but an increase in cloud cover.  It seems counter intuitive, but there you go.

Any suggestions are welcome.