The Murray Darling Basin Authority puts out a weekly report on what is happening within the basin area in term of water flows, storage levels and water allocations for the various bodies that seek water from the basin.
For the first week of each new month, usually the first paragraph is a summary of the climate for the previous month.
This weeks report starts with the following"
I have a number of questions about this statement.
1. Why is the comparison between the average temperature with a 30 year period from 1961-to 1990. One might argue that the period prior to 1961 contained not enough datapoints perhaps, but why stop at 1990? Why is that 30 year period chosen as the Average Australian temperature?
2. Secondly, why compare a mean temperature for September to an average..
The writers do not define which mean they refer to, as apart from the arithmetic mean, a dataset also has an harmonic mean and geometric mean.
The arithmetic mean of a set of numbers is the same as the average of the set of numbers, so one can only assume they are talking about the arithmetic mean. So why not use the word average? They did not use the word mean in the statement about the values from 1960 to 1990.
3. For the basin itself, which he minimum temperatures were mostly average to above average, whilst maximum temperatures were mostly below average to to very much below average, it would seem logical that the average temperature then was somewhat below average, but they do not provide how much below average.the MBA takes in a tad over 14% of the OZ land mass, so for the rest of Australia, there must have been some pretty hot places to get the average up to 0.69 above the 30 year average.
4. The concept of an average temperature is contentious.
I would suggest that if you asked a 100 Australians how the average temperature for Australia is derived, they would say that you add up all the maximum temperatures for the day, and divide it by the number of recording stations. However, if one looks at the
September BOM Report , one can see that the average is actually average of the days highest and lowest temperatures. So when the BOm says that the daily, weekly or monthly temperature is 0.69 above the long term average, that result can be achieved by having a higher Max, a higher minimum, or a combination of both. if we are told that the earth is warming at rate X, one needs to ask is it because the maximum temperatures have increased, or because the minimum temperatures have increased. Either can achieve the average anomaly increase, but your average punter would see the outcome entirely differently.
Mick