Century trends in Victorian temperatures

There are a dozen or so rural Victorian weather stations, of the 255 listed as reporting maximum temperature data to the Australian Bureau of Meteorology, that have records stretching back to years before 1900. I have found them by skimming through the listings on this page at the BOM website. It has a helpful graphic that dynamically displays the record length.

I thought it might be interesting to see the trend of maximum temperatures in these rural locations. The graphic (click the thumbnail) shows that in eight of these twelve sites, including one NSW site—Deniliquin, almost on the Victorian border—the temperature trend is negative or flat. The trend estimate is a simple, linear least-squares trend over the longest period available in each record with 1-sigma bands as indicated. The idea for this experiment came from a post at the Carbon-Sense Coalition website.

It is difficult to vouch for the quality of these records. The lighthouses at Gabo Island, Wilson's Promontory and Cape Ottway are isolated locations where there is no danger of urban heat island distortion. Other records, such as that from Maryborough, have been made at stations that once may have been located on the edge of a large town but are now engulfed by it. Still others, such as Ballarat Aerodrome appear from satellite images to be in open spaces, but still on the margins of a rural city.

It is also difficult to tell from the records or the site information provided by the BOM whether the records for each station are from a single location or a moveable location. Some—such as Ballarat Aerodrome—seem likely to represent a series cobbled together from different locations over the course of a century. Others, such as Gabo Island Lighthouse or Wilson's Promontory Lighthouse could easily be from a single location.

The full list of stations, in the row-order of the graphic, is

1. Ballarat Aerodrome
2. Cape Ottway Lighthouse
3. Deniliquin (NSW)
4. Durdidwarrah
5. Gabo Island Lighthouse
6. Horsham
7. Kerang
8. Longeranong
9. Maryborough
10. Omeo
11. Rutherglen
12. Wilson's Promontory Lighthouse

I used the following simple R script to graph the data from CSV files available here

 # data from http://www.bom.gov.au/climate/data/weather-data.shtml

 library(ggplot2)

 file<-("~/BallaratAerodrome.csv")

 df <- read.table(file, header=TRUE, sep=",", na.strings="null")

 df <- df[,3:4]

 p<-qplot(Year, Jan, data=df, main="Montly mean maximum temperature: Ballarat Aerodrome, Vic")

 p + geom_point() + geom_smooth(method = "lm")

 

Tags for this entry: climate data temperature victoria