Issue: Climate and Climate Variability in Tumut Shire

| Assessment | Implications | Background | Indicators used to assess this issue |

Assessment

Tumut was drier than average in1997 and 1998, with rainfall at the monitoring station showing results below the mean. Rainfall was about average in 1999.

March 1998 was the driest month in the three year period at Tumut, with 1mm of normal rainfall during the month. The wettest month in absolute terms was December 1999 with rainfall 127% above average (see Rainfall and its variability).

A high degree of year-to-year variation in rainfall is typical of the Tumut area. The Southern Oscillation Index (SOI), which is calculated from atmospheric pressure measurements and other parameters, indicates the state of the El Niño–La Niña Southern Oscillation. When negative, it usually implies a greater likelihood of reduced rainfall in the region. The SOI over the past decade was lower than the values in the remainder of the twentieth century as a whole, reflecting a higher prevalence of dry conditions in eastern Australia. However, during the reporting period, the SOI changed towards the positive.

The official Bureau of Meteorology station in Tumut closed in 1994, so recent temperature data are not available for this Shire (see Temperature and its variability).

Now that records and research have revealed some detail of how naturally variable our climate can be, we should avoid being fooled by periods of lush and pleasant conditions—even if they last many years. Adjusting to long periods without rain and to the energy demands on days of extreme heat must be integral to all planning decisions.

Implications

The rainfall record since 1886 has allowed us to form some idea of Tumut's long-term climate. An accurate assessment of climate is essential for two main reasons:

• planning purposes—for example, to find out how often and thus how likely is a severe deluge, drought or hailstorm—which is important in the design of buildings and infrastructure and for agriculture
• detecting climate change. We cannot be sure if, and in what direction, the climate is changing unless we know what it was to start with.

We now know that Tumut has a natural degree of climate variability and that periods of reduced or increased rainfall can occur partly as a result of the El Niño-Southern Oscillation (ENSO). However, analysis has shown that ENSO is not such a major influence on our climate as it is for other regions. Using various statistical filters it is possible to describe and measure the extent of variability. Regularly comparing the latest climatic data against long-term records can reveal small changes in the recent climate. However, it is unclear whether changes are themselves part of the natural picture—i.e., whether natural oscillations in temperature and rainfall may occur over periods too long to be detected.

However, far more data, over a much longer period, would be needed before an unambiguous Greenhouse signal would be detectable in the local records. Global atmospheric temperature data and satellite-measured sea surface temperatures make a more telling case for Greenhouse-induced climate change. But even with this, it is still not completely clear whether observed changes in global climate are part of the natural variability or not.

This does not mean that we should not take the enhanced Greenhouse effect seriously. The 'no-regrets' position is that action should be taken before absolute proof is available, because such proof could be a long time coming. The NSW Government established the Sustainable Energy Development Authority in 1996 with the aim of reducing greenhouse gases by investing in the commercialisation and use of sustainable energy technologies.

Climate remains of importance to all who live in the Region. Occasional floods or rainfall deficits, the number of frosts or of days above 30°C, all affect resource consumption, agriculture and our quality of life but are beyond our power to change.

If changes in the planet's heat budget brought about by human activities are warming all climates and increasing the likelihood of extreme climatic events, then it is in our interest to try to stop this, and to adjust to what we think is coming. Clearly, Tumut cannot alter global warming but we are under a moral obligation, as well as a legal one by international agreement, to do our 'bit' to reduce Greenhouse emissions.

The question is 'How can the public be encouraged to be better environmental citizens?' Some suggestions have been:

• Establish Government programs that offer incentives to bring about change rather than expecting people to pay more for alternative energy through schemes such as Greenpower or Earthsaver. Such incentives could take the form of subsidies, zero-interest loans or deferred payment schemes. Increasing prices for conventional energy, in relation to the tonnes of carbon dioxide equivalents released per unit of energy, would act as a disincentive, or stick. This would also be a way of paying for the incentives.
• Establish a Regional approach to weather monitoring because of the importance of collecting thorough, reliable and consistent records in as many places as practicable, to establish an accurate record of climate in the Region.
• Governments should encourage research into renewable energy sources such as sun, wind, biomass and water flow.

Reductions in the level of production and emission of Greenhouse gases may well bring improved air quality, and human health benefits, as well as the projected arrest of the enhanced Greenhouse effect.

Background

Climate is hard to define. Different from weather, although made up of it, climate is taken to be a generalisation of the weather in an area over a very long timespan. But although climate is the synthesis of day-to-day weather, it does not consist merely of means or averages. This is because a flood and a drought do not cancel each other out—each one is a climatic event. Just because, over many years, the excess rain of a deluge and the deficit of a drought may be equal in amount is of little comfort.

Climate must therefore take account of variability and the extent of the extremes. Quoting an average rainfall figure of, say, 600 mm per year, is meaningless without knowing whether the rain falls regularly in small doses, throughout the year, or tends to come in just a few major events, leaving the country dry the rest of the time.

Some climates are warmer, colder, wetter or drier than others. In the same way, some are inherently more variable than others. Tumut's rainfall is naturally erratic, with considerable variation between years. These 'droughts and flooding rains' are typical of our climate type.

The main determinants of climate are latitude, elevation, air and ocean currents, landmass, relief and other topographic features, and distance from the sea.

Climatologists have described and classified the Earth's major climatic zones. However, any description of a climate must always be somewhat 'fuzzy' because it is only through records over long periods of time that climate is revealed. This is especially true when trying to assess natural variation. A visit to a temperate region for a month in winter gives little idea of its climate in summer. In the same way, a few decades of records is far too short a time to assess natural climatic variability.

Indicators used to assess this issue