A visit to Genoa etc

 I decided to go to Genoa on 22 June to check for Cattle Egrets and (being very hopeful) the Emu.  I also went out on the new bridge to check the water level in the River.  Quite a good flow, but still plenty of sand visible.

The BoM shows that water level at the flood gauge (about 12km upstream) is well below any of the flood levels.

My birding started on the far side of the village looking out over the paddocks for the Emu. it wasn't there, and hasn't been seen for some time.  However a pair (making a few judgements about their level of friendliness) of Brown Falcons were perched on the windmill.

After checking the River I crossed the highway and spotted a single Cattle Egret with some Herefords.

Pulling into the gravel patch there were a lot of waterfowl  on the main pool.  I counted 218 Pacific Black Ducks, which was not well received by the eBird tolerance monitor until I put in a comment.  My full checklist is here.  The white breasts of the 33 Masked Lapwings stood out well.

It is not unusual to find a few Australian Shelduck here but a count of 21 was higher than normal.  It seemed that various forms of pair bonding (and aggression between the males) were going on.

On the Sunday I went to the airport.  It was a swamp: I spent quite a bit of time in 4WD on the basis that prophylaxis is more efficient than therapy!  Best bird was a Tawny-crowned Honeyeater on the fence near the terminal.

Cumulative rainfall

 This post is an approach to stating the bleedin' obvious: 2022 was a very damp year.

On 31 December the ABC published an article showing the progress of rainfall year-to-date through 2022.  The driver of this was that for some locations 2022 ended with record rainfall.  This snip shows the chart for Melbourne.

A more spectacular, and thus more beloved by journalists, example is offered by the Chart for Sydney.

I have had an attempt at creating a similar chart for Mallacoota.  I have melded data from my weather station (WS) commencing in February 2019 with BoM data recorded at the Mallacoota Airport site for 39 years over the period  January 1975 to January 2019 (4 years in the 1980s are excluded due to missing data. In the past I have found the BoM data and my WS data to be highly correlated so believe this merger is acceptable, especially in view of the amount of 'fiddling about' that would be required to get the BoM data into the same format.

The basic approach was to assemble a table showing the rainfall for each day for each year and compile from this the cumulative rainfall for each year.  I then calculated the mean cumulative rainfall for each day and the standard deviation for that mean.  Consulting a table showing the areas under a normal curve showed that plotting the lines for Mean+/- (1.288 SD) would show a range equivalent to an 80% probability of the rainfall falling within that area. That is the space between the blue and orange lines in this chart. The grey line is the record for 2022, clearly above the upper bound of the 80% range from day 69 (8 March) onwards.  The big leap for 2022 is on days 93-94 (2nd and 3rd April).

A technical issue at this point is that the probabilities are based on the data showing a normal distribution - the famous bell shaped curve.  That is certainly not the case when looking at cumulative rainfall year to date.  So I go back to the (what I think is) ABC approach of looking at the values recorded in 80% of years: I assume they have removed the top 10% and bottom 10% of records.  Learning a few things about EXCEL along the way I applied the PERCENTILE function to plot the values the 90% and 10% percentiles giving the following chart.

I have added to the chart a maximum line plotting the highest cumulation recorded: this overlies the 2022 line for a couple of months but then the maximum line moves away due to heavier falls in June 1978 and October-November 1985.

My final chart includes the median cumulant for each day.  That measure is the value with half values above it and half below: it avoids the biasing impact of large outliers that boost the arithmetic mean, and is my preferred measure of "average" for rainfall.

Rain event 15-16 August

 Last weekend the BoM forecast Floodmageddon and we scored a total of 5.4 mm.  This weekend the forecast was more restrained so I was expecting zip.  However Hughie has been sending 'er down.  Yesterday we ended with 40.4 mm and today thus far (to 1500 hrs my Weather Station has recorded 35.8 mm.

The BoM site has recorded somewhat more as the system sending the moisture is to our West and we, and the Gabo Island site, are just getting the edge of it.

I was beginning to suffer from cabin fever so went for a drive to see what was occurring.  Its a reverse of a few weeks ago when the water was coming up from the Inlet.  Today it's definitely going the other way.

Mullet Creek usually has no flow: its got a bit today.

A paddock on Sunny Corner.  Not too sunny today!

Distant run-off on the edge of the Park, seen dimly through the rain.

Closer run off!

In part my outing was inspired by a video of water running across Bastion Beach.  Here is the deluge coming under the new steps.

And here is the source of the deluge,  I now understand the comment on FB about needing to unblock the drain!

While out at Bucklands I noticed a lot of Gastrodia sesamoides, also know as Potato Vine.

The raindrops were also quite artistic!

On the Monday 17 August the level of the Inlet was obviously up soI checked the depth gauge at the wharf.  It was basically back to where it was before the big rise which led to the opening.

Measures of rain at Mallacoota

I noticed on 23 May that the rainfall recorded at the BoM site for Mallacoota was a lot less each hour than I was recording at home.  Several members of the Mallacoota community provided me with their cumulative readings and they were very consistent with my readings.  I drove to some spots near the BoM site and the amount of water lying in ditches and the beach erosion by a small creek draining the area near the BoM site suggested to me that the BoM installation was well under-recordng the rain.

I was thus surprised to find that by early on 24 May the BoM had "caught up".  This led me to investigate the falls for various times and I find the BoM readings to be extremely strange.  I then included the readings from a wunderground site in the centre of Mallacoota under the name of Putz (the nickname of the site owner).  The location of the three sites is shown here.

A chart of the three series for the period 0100 hrs on 23 May to 0500 hrs on 24 May ....

... gives a very strange picture.  There is very close agreement between my Weather Station and Putz but the pattern shown by the BoM site is very different.  Were this during a period of thunderstorms or small intense rain cells I could understand the differences.  However this event was very staedy gentle rain over several hours.  Also the ground evidence of significant rain represented by the images linked above suggests the BoM record is well understated.

The final straw in the wind (straw in the rain?) is theat the wind direction through the day was consistently SW-WSW at my site so the weather was coming amost in a straight line from the BoM over Putz to my site!

I shall raise this with BoM.

Rain event 22-2? May 2020

A signal that things were going to get damp came in the forecasts earlier in the week.

As knowledgeable meteorologists have pointed out it is theoretically wrong to add up these percentiles, but I can't see how else to estimate the event total from available data.

A chronology of musings early in the day of 23 May.

On the morning of 23 May it was evident that bizarreness is going on with rainfall measuring. My weather station has recorded 45 mm of rain in the last 24 hours (to 0500, 23 May). Another station near the Medical Centre has recorded 42 mm to that time. (20.2 mm fell on the 22nd, while 23.8 filled up the gauge before 0500 on the 23rd. Another 4 mm has arrived between 0500 and 0600 on the 23rd.)

BoM, near the airport has recorded 8.2 mm and Gabo Island 28.8.

Looking at the radar image

... suggests that this area is right on the extreme of the rain area, but such a marked difference, for what appears to be steady rain is surprising.

My WS was up to 56.4 mm for the event (36.2 mm since midnight). With a month to date fall of 74.4 mm we are well past the median fall for May (68 mm) and closing in on the mean (80.8 mm).

At around that time  I posted a message on various Facebook groups seeking other people's observations.  We then went for our morning walk walk noting that there was a fair run-off in places.

Reports from elsewhere in Mallacoota

A resident from Betka Rd noted " I was just looking at bomb, thinking noooo way, 13mls, my pond flooded tells me it was a good drop. "

Another resident on Intervale Drive noted 59mm up to 0800.

68 mm at Karbeethong

Later in the day a local identity posted a photo from Bastion Point noting 59 mm which drew a response from near the Narrows of  "We are up to about 70 m l s"

In summary it seems that most people, covering the town area quite well, were recording somewhat over 65 mm.  Or, as expressed to me by a traditionalist, close to 3 inches.

Following up

The rain continued steadily, around 5mm/hr up until about 1400 hrs.

By that time my WS was up to 57.8 mm for the day and the event was  at 81 mm at home.  BoM were still at 29.2mm for the event.

So I took myself for a drive to the mid-West, which in terms of Mallacoota is Betka Beach, Quarry Beach and the Airport.  In effect circling the BoM site.  The beach at Betka was rather damp and the kelp had been hurled up on top of the bar but, despite the helpful surf, it didn't look as though the sea was about to break through.

 Surf was also up a Quarry Beach and there was fair evidence that the Creek beside the car, which drains the paddock in which the BoM site is located had had fair run off.

 On the far side of the Airport a drain was replete.  I think it would have taken more than 28 mm to have achieved that!

 My final stop was at the official depth gauge for the Inlet.  That is currently sitting at 0.46 m. 

It will be interesting to see how far it rises.  Had the rain gone inland and soaked the whole catchment a significant rise might have occurred.  However Bombala AWS had recorded no rain, so I would be surprised if the event causes much of a rise in the level of the Inlet.  A low rise would also be indicted by the steady, soaking nature of the rain.  Excellent for recharging the soil and growing plants!

Rainy days

Back in the day a meteorologist commented that it took 5 mm of rain to do more than lay the dust.  This was in the context of trying to maintain a vegetable garden in Canberra under level 3 water restrictions.  I thought it might be interesting to look at BoM records for Mallacoota to assess the number of days per year with falls of 5mm or more.  That is summarised in the following chart.

There is no trend in the data but the downward tendency of the last 4 years is quite obvious.  I have included the data for Gabo Island as a crude form of quality assurance and as the series have a correlation coefficient of 0.76 the pattern can be rated as quite similar.  This also "plugs the gap" in the mainland data from 1979-83 where several months are either totally missing or - in the case of 1979 and 1983 - monthly totals are given but many daily totals are missing.  Interestingly, where daily totals are given in 1980 and 1983 a high proportion are well over 20 mm: given the appearance of an arrow symbol in the table above many of these I believe them to be the situation described by BoM as

"For observations of daily rainfall which span more than one day it indicates that there is some uncertainty associated with the exact date on which the daily rainfall occurred."

This illustrates the need to look at the detail of the data and not just the numbers.

I also compared the number of days with falls >5 mm with the number >0.2 mm (the latter being to exclude days with a heavy fog rather than rain).

This illustrates the problem as being lack of sustained rainfall >5mm: the number of days with falls between 0.4 and 4.8 mm is about normal.

How dry is it?

On the Mallacoota Community Facebook group a few members have been asking questions along the lines of "Why is this year different in terms of fire risk?".  Robin Bryant has answered this by quoting the CFA assessment (emphasis added):

The CFA assessment of 16 December is ... The outlook suggests that above-normal bushfire activity will continue across the coastal and foothill areas of East and West Gippsland, across to the Great Dividing Range, however this now extends west to also includes the Central Goldfields, which takes in parts of the Wimmera and Mallee.

This is due to above average temperatures drying out grasslands and forests over the last three months coupled with three years of significant rainfall deficit in much of East Gippsland and across the Divide. While there has been spring rain in the south, much of inland Victoria received insufficient rainfall and as a result, soil moisture is lower compared to the long-term average.

When grasses and crops are close to fully dry, there is a very high potential for fire behavior to rapidly escalate under elevated fire weather conditions.

I thought it worthwhile illustrating the rainfall deficit.  These data are from the BoM site out near the airport, beginning with the annual totals (I have assumed that we are going to get no more rain in the last three days of December).

Its a pity that there are a few years missing, but such is life.  The decline in the last three years is very evident ending with 2019 being the lowest on record at 595 mm.  (There are only two other years below 700 mm.)

The missing years place difficulties in getting a 3 year series with a lot of observations but it is a good bit smoother than the annual data. This show a high plateau early on, followed by a lower plateau and then the drop-off in the last three years.

Further insights can be gained by looking at the data recorded by BoM for Timbillica, just across the NSW border. This typically has an orographic component to its falls as the air from coast rises as it meets the hills.  This site has very good data with only 1 year missing back to 1910.  (December data for 2019 is not yet available for this site so I have estimated it as 50% more than the December fall for Mallacoota.)  The annual values show a lot of variation and I have cut to the chase with triennial data.

The trend line is essentially flat due to variation over time.  However the three year total ending in 2019 is very low: only the years 1981-82 are lower.  So, again, this period is unusually dry.