Inland basin frost anomalies and the Taieri Plain

[Richard]

Waiau at the top and of the Amuri plains recorded -4.1, -4.1 and -2.4 over the last three mornings. Culverden -4, -4.8 and -2.
Wasnt to many years ago this area received colder frosts than the Canterbury plains, nowadays not so. The climate here was 20 years ago was closer to the likes of Alexander. When comparing the Taieri plains to the Amuri plains, both surrounded by hill ranges, the Taieri is closer to sea level and to the sea, yet had a -8 deg. Why has the Amuri warmed so much, has it anything to do with dairy farming?

[Dean.]

Waiau at the top and of the Amuri plains recorded -4.1, -4.1 and -2.4 over the last three mornings. Culverden -4, -4.8 and -2.
Wasnt to many years ago this area received colder frosts than the Canterbury plains, nowadays not so. The climate here was 20 years ago was closer to the likes of Alexander. When comparing the Taieri plains to the Amuri plains, both surrounded by hill ranges, the Taieri is closer to sea level and to the sea, yet had a -8 deg. Why has the Amuri warmed so much, has it anything to do with dairy farming?

More wind....

[spwill]

Waiau at the top and of the Amuri plains recorded -4.1, -4.1 and -2.4 over the last three mornings. Culverden -4, -4.8 and -2.
Wasnt to many years ago this area received colder frosts than the Canterbury plains, nowadays not so. The climate here was 20 years ago was closer to the likes of Alexander. When comparing the Taieri plains to the Amuri plains, both surrounded by hill ranges, the Taieri is closer to sea level and to the sea, yet had a -8 deg. Why has the Amuri warmed so much, has it anything to do with dairy farming?

There is always the question of how accurate are the temperature readings from the Taieri .
The Taieri Plains near Dunedin airport are 2 metres below sea level, the lowest point in NZ.

Some parts of NZ that have been marginal for frost occurrence in the past will be becoming frost free. No frost recorded here this Winter yet.

[TonyT]

Why has the Amuri warmed so much, has it anything to do with dairy farming?

Yes, higher humidity from greater soil moisture due to irrigation and denser grass cover.

[Richard]

Why has the Amuri warmed so much, has it anything to do with dairy farming?

Yes, higher humidity from greater soil moisture due to irrigation and denser grass cover.

I think your points raised are more relevant to the growing season Tony, not winter, this time of year with rape grazing, by Aug there would be 100's hectares of mud/bare soil, so there would be less grass cover now than before the dairy boom.

[Richard]

Waiau at the top and of the Amuri plains recorded -4.1, -4.1 and -2.4 over the last three mornings. Culverden -4, -4.8 and -2.
Wasnt to many years ago this area received colder frosts than the Canterbury plains, nowadays not so. The climate here was 20 years ago was closer to the likes of Alexander. When comparing the Taieri plains to the Amuri plains, both surrounded by hill ranges, the Taieri is closer to sea level and to the sea, yet had a -8 deg. Why has the Amuri warmed so much, has it anything to do with dairy farming?

More wind....

No dont think so, frosty nights are always nearly calm

[Richard]

There is always the question of how accurate are the temperature readings from the Taieri .
The Taieri Plains near Dunedin airport are 2 metres below sea level, the lowest point in NZ.

How does accumulating rainfall drain way if its below sea level, do they pump it out.

Some parts of NZ that have been marginal for frost occurrence in the past will be becoming frost free. No frost recorded here this Winter yet.

Its likely the frosts temps in some areas are warming more than others, areas west of CHCH/ Rangiora/ Oxford dont appear to be to the same extent. Be interesting to compare 30 years ago to now, maybe Nev could find these stats

[spwill]

The lowest point on the Taieri Plains sits above the low tide level so water can get away then. During heavy rain events ponding will occur particularly around Henley. I think it was 1980 when Dunedin airport was out of action for quite some time due to flooding. Building the airport at that location was possibly a mistake although it has not flooded since.

[Richard]

Mods may want to split off into Off Topic

What I'm I missing here, parts of the land surface on the Taieri's are 2m below sea level, yet at times tide heights at the mouth can be 1.7m, could be wrong but I didn't think the Taieri/Waipori river was tidal up as far as the plains, I know they say it is but go look on google map street view from the bridges, all 15 photos from 4 different bridges all show the same river level, remarkable timing for the google car to pass over the bridge right at high tide.

It doesn't add up

[Richard]

... thinking more about whether the Taieri river does have tides, if it does have tides low enough to be able to drain land 2m below sealevel then lakes Waihola and Waipori would be tidal also, if that were the case there would be huge amounts of water surging up and down the Waipori river from the mouth, the mouth itself would a lot deeper because of massive flows in and out. The Waihola and Waipori would be estuaries and not lakes

[snowstormwatcher]

... thinking more about whether the Taieri river does have tides, if it does have tides low enough to be able to drain land 2m below sealevel then lakes Waihola and Waipori would be tidal also, if that were the case there would be huge amounts of water surging up and down the Waipori river from the mouth, the mouth itself would a lot deeper because of massive flows in and out. The Waihola and Waipori would be estuaries and not lakes

Lake Waihola is definitely tidal,I've seen Yellow eyed Mullet in there which I'm sure require at least some saltwater to survive, also caught a Kahawai while fishing the Taieri river near Henley so again definitely some tidal influence.

[Richard]

... thinking more about whether the Taieri river does have tides, if it does have tides low enough to be able to drain land 2m below sealevel then lakes Waihola and Waipori would be tidal also, if that were the case there would be huge amounts of water surging up and down the Waipori river from the mouth, the mouth itself would a lot deeper because of massive flows in and out. The Waihola and Waipori would be estuaries and not lakes

Lake Waihola is definitely tidal,I've seen Yellow eyed Mullet in there which I'm sure require at least some saltwater to survive, also caught a Kahawai while fishing the Taieri river near Henley so again definitely some tidal influence.

I just spoke to the owner of the Waihola motor camp and he said there is a small tide, he reckons i goes up and down by about 30-40cm, not 2m needed to drain that below sea level land.

[Nev]

Mods may want to split off into Off Topic

Mod Note: For want of a better title, I've split this thread from the 'Frosts 2022' thread.

[spwill]

... thinking more about whether the Taieri river does have tides, if it does have tides low enough to be able to drain land 2m below sealevel then lakes Waihola and Waipori would be tidal also, if that were the case there would be huge amounts of water surging up and down the Waipori river from the mouth, the mouth itself would a lot deeper because of massive flows in and out. The Waihola and Waipori would be estuaries and not lakes

Swampland was drained to create very fertile farming land with stopbanks to protect lowest areas from flooding. The area does flood easily during the big rain events, mostly from water coming down the Taieri river from the hill country to the west/NW.

[Richard]

Yes agree, stop banks protect during floods, during normal river flows the tides arent low enough to drain 2m below sea. Its either that its pumped out or its not correct that some of the land is as low as claimed.

[spwill]

Yes agree, stop banks protect during floods, during normal river flows the tides arent low enough to drain 2m below sea. Its either that its pumped out or its not correct that some of the land is as low as claimed.

They do use pumps. I think at low tide much of it is above the actual sea level

[Richard]

Yes agree, stop banks protect during floods, during normal river flows the tides arent low enough to drain 2m below sea. Its either that its pumped out or its not correct that some of the land is as low as claimed.

I think at low tide much of it is above the actual sea level

But it cant be, if its 2m below

[kiwisk8er]

I live in Mosgiel, we had three frosts last week that were colder than -5. A number of things come into play with the Taieri plain. Even though we are close to the sea, the hills and mountain ranges completely cut off Mosgiel and the airport from the sea. On foggy days in Dunedin, the sea fog doesn't reach Mosgiel at all, the hills and mountains protect us.

Taieri Plains are always hotter than Dunedin in summer, and colder and frostier in winter. Mosgiel tends to be sunnier than Dunedin.

During the cold weather this week Mosgiel and the Taieri plains were trapped under an inversion layer quite low to the ground. We live in a two story house and we could look out over Mosgiel and see how low the inversion layer was thanks to everyone's fires going. The cold air was trapped underneath it. During the day anything in the shade just wouldn't defrost.

The thing about the airport is that it is in line with the Maungatua range which is 895 m above sea level. The cold air from the top of the mountain sinks directly onto the airport. When there is snow on top it makes the airport and Momona super cold.

Personally I use the local weather stations to get an idea of Mosgiel's weather, rather than the airport as they are always colder than in Mosgiel. The sun coming up over Flagstaff to the east doesn't happen until around 9 am at the moment so the local weather stations are pretty reliable with temperatures overnight.

[Simon Culling]

Minimums of -8°C/-9*C without a snow cover at 45 degrees south and close to the coast is pretty impressive. For southern England, which is at around 51 degrees north, the likely minimum without a snow cover and for most rural locations (but not frost hollows) is around -10*C as a comparison.

Two questions - how low might the temperature go if there was a decent snow cover? and what is the average monthly minimum at the airport for the three winter months? The figures on the Dunedin wikipedia page are around 3*C/4*C, so I am guessing this is for the city.

[Nev]

Two questions - how low might the temperature go if there was a decent snow cover? and what is the average monthly minimum at the airport for the three winter months? The figures on the Dunedin wikipedia page are around 3*C/4*C, so I am guessing this is for the city.

Dunedin Aero's 1981-2010 average T-min for June, July and August are 0.5C, -0.6C and 0.9C respectively. Its lowest all time temp of -8.8C was recorded on 27 May 2021, 08 July 2007 and 28 May 1988, since records began in 1963. No record of snow for the May events, but there was snow for the July event.

[spwill]

I think at low tide much of it is above the actual sea level

But it cant be, if its 2m below

I guess it comes down the definition of sea level high tide, mid tide or low tide.

[spwill]

Minimums of -8°C/-9*C without a snow cover at 45 degrees south and close to the coast is pretty impressive. For southern England, which is at around 51 degrees north, the likely minimum without a snow cover and for most rural locations (but not frost hollows) is around -10*C as a comparison.

Two questions - how low might the temperature go if there was a decent snow cover? and what is the average monthly minimum at the airport for the three winter months? The figures on the Dunedin wikipedia page are around 3*C/4*C, so I am guessing this is for the city.

Snow wont hang around like it can do in England at low levels, snow at Dunedin airport is nearly always gone within two days.

Perhaps the clean atmosphere this part of the world allows for more cooling.

[Richard]

But it cant be, if its 2m below

I guess it comes down the definition of sea level high tide, mid tide or low tide.

I thought sea level was the halfway point between the highs and lows, averaged out.
Looking on google maps, no pump stations can be seen, only a flood gate. I'm now convinced there's no land below sea level on the Taieri's.

[spwill]

I guess it comes down the definition of sea level high tide, mid tide or low tide.

I thought sea level was the halfway point between the highs and lows, averaged out.
Looking on google maps, no pump stations can be seen, only a flood gate. I'm now convinced there's no land below sea level on the Taieri's.

This might be worth looking at, there is an elevation map here.. https://www.orc.govt.nz/media/5009/natu ... report.pdf

[einzack]

This might be worth looking at, there is an elevation map here.. https://www.orc.govt.nz/media/5009/natu ... report.pdf

Thanks, great doc. One of many interesting and relevant figures attached for speed.