Melbourne Urban Heat Island Contamination of Temperature Trend Maps in Victoria, Australia
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Nonlinear Engineering, Vol. 2 (2013), pp. 39–62 Copyright © 2013 De Gruyter. DOI 10.1515/nleng-2013-0006 Melbourne urban heat island contamination of temperature trend maps in Victoria, Australia 1; Albert Parker activities, and the thermal inertia is also increased by the presence of industrial materials such as roads and buildings 1 RMIT University, PO Box 71 Bundoora VIC 3083, Mel- (the heat island effect). bourne, Australia Abstract. The paper presents a regression analysis of the temperature data measured by the Australian Bureau of Me- teorology in their historical measuring stations in Victoria. All the downloaded data was free of quality issues and re- ferred to specific geographical locations, with only minor gaps in the recorded data. Temperatures at stations located in regional Victoria show no growth in the long, medium and short term. Temperatures in the greater Melbourne area show growth biased by the establishment of a metropolitan heat island. Corrected for the heat island effect, the temper- ature changes are minimal. Keywords. pattern recognition, temperature records, heat island effect, Victoria, Australia. 1 Trend maps and local temperature results The population of Australia is estimated to be more than 22.5 million over an area of 7,617,930 km2. The population is concentrated mainly in urban areas, with Melbourne and Sydney accounting for about 4 million each. Victoria is the second most populous state in Australia and geographically the smallest mainland state, with a population estimated to be more than 5.5 million over an area of 237,629 km2. Aus- tralia has an extensive network of meteorological measur- ing stations many of which have been operational for more Figure 1. Australian Government Bureau of Meteorol- than a century; some measuring stations have started oper- ogy. Australian climate variability & change Trend maps ation very recently, and others have been discontinued [1- (from [1]). 4]. Most of the newly established stations are located in fast growing areas, while most of the stations with longer The Australian Government Bureau of Meteorology [1] records disconnected were located in remote country areas. presents trend maps of generalized warming for Australia The relative weight of measuring stations in fast growing as presented in Figure 1. The maps are available for periods urban areas vs. stations in country areas has been dramati- 1910-present to 1970-present every 10 years. cally increased recently. It has been shown already [23] that for the specific loca- In measuring stations located in fast growing urban ar- tion of the Northern Territory these trend maps show strong eas, an increasing amount of thermal energy is being re- warming especially in the central Australian desert, where leased because of the increasing population and productive Alice Springs is the only established measuring station, a conclusion that is not supported by the actual thermometer Corresponding author: measurements. There is a similar lack of experimental evi- Albert Parker, E-mail: [email protected]. dence for the warming depicted on these summary maps in Received: 18 March 2013. Accepted: 4 June 2013. Victoria also, as shown in this paper. 40 A. Parker Heat island build-up is a well-known bias that occurs in region has a growing population now in excess of 4 million recorded temperatures of urban areas [5-18]. The urban people and with a long-term population growth projected at heat island (UHI) of Melbourne is analyzed in details in 1.3 per cent a year. When the Melbourne regional office [16-17]. The analysis of [17] concludes “it appears to be station commenced operation in 1908, the thermal inertia very difficult to make allowances for any UHI effects when of the area surrounding the measurement location as well analyzing temperatures and therefore difficult to dismiss the as the amount of energy being released about the measure- possibility that UHI effects are creating a false impression ment location, were definitively negligible by comparison of global warming.” Small towns in regional Victoria also with today, and this heat build-up will certainly have af- display an UHI [18], even if obviously less significant. At fected the reading of the thermometer. the same time that temperatures recorded in the greater Mel- bourne metropolitan area show a warming, the temperatures recorded in regional Victoria show no long term warming 2 Local temperature regression analyses with various trend. time windows This statement is supported by the temperature database of historical measuring stations used by the Australian Bu- To better understand the warming trends it is therefore nec- reau of Meteorology [5] in their synthetic statistical and essary to consider individually all the stations with a sig- yearly averaged temperatures. The data available in this nificant number of years of operation, and correct the data compilation are the historical highest and lowest and 2010 for all possible biasing factors, first and foremost of which values, plus the yearly averaged maximum and minimum is the heat island effect. Of all 14 high quality historical mean temperatures. These data are described in the sup- measuring stations with longer records of Victoria [3] con- porting material. The stations considered in detail in this sidered, ECHUCA, BALLARAT, MELBOURNE, CAPE paper are listed in Table 1. OTWAY and WILSON PROMONTORY are selected here For most of the locations considered the mean maximum analysis in order to provide a more accurate regional tem- and minimum temperatures lie near the mean values over perature record. Each station is first analysed individually all the years [5], and the time series of yearly averaged tem- in order to understand the individual trends at stations with peratures do not show any warming. The heat island effect little heat island effect. appears to be significant especially in the downtown Mel- From the list of Australian meteorology stations open bourne location, where the temperatures are always above for more than 50 years [3] those still operational in Vic- the mean local values over all the years. toria are used to serve as a good basis for estimating the From the synthetic statistical and yearly averaged tem- average trend for temperature across in the whole state. peratures proposed by the Australian Bureau of Meteorol- To show the influence of the heat island build up on the ogy [5], the temperature changes at specific station loca- measured temperature and also to assess better the current tions over the available times of record are as follows: MIL- trends for temperature in Victoria, the raw data of monthly DURA is marginally warming in the mean maximum and mean maximum and minimum temperatures have therefore almost unchanged in the mean minimum. HORSHAM and been downloaded from the Australian Bureau of Meteorol- RUTHERGLEN are slightly cooling in both temperatures. ogy [4] and analyzed with different statistics. ORBOST is slightly warming in both mean temperatures. WILSONS PROMONTORY is warming in the mean min- 2.1 Long term (100-150 years) statistic imum and steady in the mean maximum. MELBOURNE is warming significantly especially in the mean minimum The last 100-150 years raw monthly mean maximum temperature. BALLARAT is cooling in the mean minimum and minimum temperatures for the Ballarat Aerodrome, and unchanged in the mean maximum. CAPE OTWAY Cape Otway Lighthouse, Melbourne regional office, Wilson is cooling in the mean maximum and unchanged in the Promontory Lighthouse and Echuca Aerodrome measuring mean minimum. CASTERTON is marginally warming in stations are presented in Figure 2. The 12 months moving the mean maximum and unchanged in the mean minimum. average is also superimposed to the raw data to understand LAVERTON (within the greater Melbourne metropolitan the trends. Linear (solid black line) and second order poly- area) is warming. SALE is marginally warming in the mean nomial (dotted line) fittings are also applied. These results maximum and unchanged in the mean minimum. OUYEN show clearly that temperatures are not increasing at Bal- is unchanged in both mean temperatures. GABO ISLAND larat, Cape Otway, Wilson Promontory and Echuca, while is unchanged in both mean temperatures. ECHUCA is in Melbourne the temperatures, especially the mean mini- slightly cooling in the mean minimum and unchanged in mum temperature, are slightly higher now than in the past. the mean maximum. The long term linear statistics tell us that: The null hypothesis for the warming shown at Mel- In Ballarat the maximum temperature is slightly in- bourne is that it results from the build-up of an urban heat creasing (0.00778°C/year) but the minimum temper- island around the measurement location. The Melbourne ature is slightly decreasing ( 0:0050°C/year); Melbourne urban heat island contamination of temperature trend maps in Victoria, Australia 41 (a) BALLARAT AERODROME. Commenced: 1908; Latitude: 37.51ı S; Longitude: 143.79ı E; Elevation: 435 m. (b) CAPE OTWAY LIGHTHOUSE. Commenced: 1861; Latitude 38.86ı S; Longitude: 143.51ı E; Elevation: 82 m. (c) MELBOURNE REGIONAL OFFICE. Commenced: 1908; Latitude: 37.81ı S; Longitude: 144.97ı E; Elevation: 31 m. (d) WILSONS PROMONTORY LIGHTHOUSE. Commenced: 1872; Latitude: 39.13ı S; Longitude: 146.42ı E; Eleva- tion: 95 m. (e) ECHUCA AERODROME. Commenced: 1859; Latitude: 36.16ı S; Longitude: 144.76ı E; Elevation: 96 m. Figure 2. Last 100-150 years raw data for monthly mean maximum and minimum temperatures for selected historical measuring stations