Upper Lachlan
Please note: Text or data highlighted in this colour represent an update to this indicator for the period 2008/09. All temperature figures have been updated on this page. Evaporation and Soil Moisture have also been included in this update.
Temperature Analysis
Temperature observations are taken at Taralga Post Office (Bureau of Meteorology Station No. 070080). While the temperature record at Taralga is incomplete between 1971 and 1991, due to the high correlations with Goulburn with both maximum and minimum temperatures, a complete data set has now been developed. (Refer to Appendix 3 for details).
Note that in the following analyses temperatures for individual months are compared to the long-term average (or climatology) from 1975-2004. A 30-year period is used to calculate climatological averages to conform with World Meteorological Organisation practice; this takes into account year-to-year variations and less frequent events such as El Niño or La Niña. This particular 30-year period is used in this analysis because it is the period with the best temperature data availability across the Australian Capital Region.
The annual averages of maximum temperatures for the period 2005-2008 (Table 1 and Figure 1) were on or above the long-term mean, with 2006 having the highest average maximum temperatures since 1971. The daily maximum temperature is usually measured in the early afternoon, while the minimum temperature is usually recorded just before sunrise. Mean minimum temperatures were average for 2005, below average for 2006 and 2008 and above average for 2007. Overall mean daily temperatures, calculated as the average of the maximum and minimum temperature each day, were above average for 2005-2007 and below average for 2008.
2005 |
2006 |
2007 |
2008 |
|
|---|---|---|---|---|
| Mean Daily Maximum Temperature | 19.2 |
20.0 |
19.2 |
18.3 |
| Anomaly (oC) | 0.9 |
1.7 |
0.9 |
0 |
| Anomaly (%) | 5% |
9% |
5% |
0% |
| Mean (1975-2004) | 18.3 |
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| Mean Daily Minimum Temperature | 6.5 |
5.9 |
7.1 |
5.7 |
| Anomaly (oC) | 0.2 |
-0.4 |
0.8 |
-0.6 |
| Anomaly (%) | 3% |
-6% |
13% |
-10% |
| Mean (1975-2004) | 6.3 |
|||
| Mean Daily Mean Temperature | 12.9 |
12.9 |
13.2 |
12.0 |
| Anomaly (oC) | 0.6 |
0.6 |
0.9 |
-0.3 |
| Anomaly (%) | 5% |
5% |
7% |
-2% |
| Mean (1975-2004) | 12.3 |
|||
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In the 54-month period January 2005-June 2009 there were 41 months (76%) in which the monthly maximum temperatures were above the long-term average (Figure 2). This four year period had generally warmer monthly average daytime temperatures than the long-term mean, particularly between April 2005 and November 2007 when there were only 3 months of below average temperatures. Maximum temperature anomalies were highest in October 2006 (4.2oC above the monthly average), whereas in February 2008 the average daily maximum temperature was 3.9oC below the monthly average.
For minimum temperatures, there were 30 months (57%) with temperatures above the long-term average (Figure 2), particularly between April 2005 and March 2006, and from November 2006 to January 2008. Minimum temperature anomalies were highest in August 2007 (3.0oC above the monthly average), whereas in April 2006 the average daily minimum temperature was 2.4oC below the monthly mean.
Overall, the daily mean temperatures show a warm period with fifteen months below the long-term average. Note that an El Niño event occurred in 2006/2007; temperatures tend to be above average during these events, particularly during spring and summer. Lower temperatures in 2008 coincided with a La Niña event in 2008/2009.
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Long Term Climate Trend
It is useful to compare recent climate observations with a longer record in order to assess how unusual recent events may be. While there are gaps in the temperature record at Taralga through the 1970s and 1980s, using correlations with Goulburn has resulted in a complete data set being developed. While there is no apparent trend in minimum temperatures, maximum temperatures have increased since 1991 and five of the last 7 years have been particularly warm.
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Evaporation and Soil Moisture
Evaporation and soil moisture are important components of the moisture balance in the environment. Potential evaporation (the amount of moisture evaporated from an open water surface under prevailing conditions) occurs as a consequence of a combination of factors including incoming solar radiation, temperature, wind and the humidity of the air. The balance among the factors controls the amount of potential evaporation, so that an increase in solar radiation or temperature (which would cause evaporation to increase if all other factors remained unchanged) might be offset by a decrease in wind (which would cause evaporation to decrease). Soil moisture reflects the interaction between rainfall and evaporation, and provides an indication of the amount of moisture available for plant growth.
The variation in potential evaporation at Taralga for the period 2000-2008 is illustrated in Figure 4. There is strong seasonal variation between summer and winter, with low values in winter and high values in summer. Potential evaporation over this period shows little overall trend or change from year to year, except during the 2008-9 summer when potential evaporation increased.
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Soil moisture variations at Taralga in the upper and lower layers in the period 2000-2008 are illustrated in Figure 5. The impact of rainfall on the upper level soil moisture profile is evident in the relatively large and rapid fluctuations within the time period, which closely mirror the variability of rainfall at Taralga. The lower level soil moisture shows the effects of the extended dry period since 2000; there is an overall decline in the lower soil moisture, with any increases in moisture being relatively abrupt (following larger rainfall events) followed by longer periods of drying. The time lag in changes to the lower level soil moisture following rain events is also evident.
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About the data
Evaporation and soil moisture data were extracted from the Australian Water Availability Project (AWAP) dataset, a jointly funded project developed by CSIRO Marine and Atmospheric Research (CMAR), the Bureau of Meteorology (BoM) and the Bureau of Rural Science (BRS) to monitor the terrestrial water balance of Australia. Upper level soil depth is considered to be to a depth of 0.2m while lower level soil depth is considered to be to between 0.2m and 1.5 m.
References
M.R. Raupach, P.R. Briggs, V. Haverd, E.A. King, M. Paget and C.M. Trudinger, 2009 Australian Water Availability Project (AWAP): CSIRO Marine and Atmospheric Research Component: Final Report for Phase 3. CAWCR Technical Report No. 013. 67 pp.
