Chapter 1 Introduction

The Climate of 2001-02

The Australian climate of 2001-02 reflected the two contrasting states of the El Niño - Southern Oscillation (ENSO) phenomenon as illustrated in Figure 1.5, which depicts a continent that was under the influence of both La Niña and El Niño events during these two years. In the early months of 2001, a prevailing La Niña pattern in the equatorial Pacific Ocean dominated the weather over northern and central Australia, resulting in well above average rainfall. Alice Springs received 240 mm in four days in late January, only 40 mm below its annual average rainfall, and heavy rain soaked northern and eastern New South Wales in early February. In contrast, parts of south central and southeastern Australia experienced extreme heat during the first two weeks of January, with maximum temperatures at many centres approaching those of the infamous January 1939 heatwave.

Figure 1.5 Rainfall decile map for the 24-month period January 2001 through December 2002, showing above average rainfall in the top end and western-central interior and the very dry conditions in the east and far west.

The waning of the La Niña pattern in autumn 2001 saw a return to more normal rainfall over most of the country. Southern Victoria, suffering from below average rainfall since 1996, experienced heavy, though somewhat patchy, rain in late March and again in late April. However, southern areas of Australia experienced a mostly dry winter and early spring, associated with relatively weak mid-latitude westerly flow over the Australian sector, meaning these autumn rains in the southeast had little lasting impact upon water storages. Despite a "one-off" fall of 88.6mm late in July, Perth experienced its third driest winter on record, coming on top of an extremely dry previous nine months. As a result, water restrictions were imposed in early September.

Bushfires raging in New South Wales on 3 January 2002. Many of these fires started on Christmas Eve 2001 and burnt well into January 2002. Around 170 homes were lost, with fires reaching into the outer suburbs of Sydney.

Unusually cool conditions prevailed over the southern half of the continent in the period October through December 2001, with maximum temperatures in October and December averaging up to 3-5ºC below average over south central Australia. In contrast, hot, dry north-westerly winds late in December resulted in disastrous bush-fires centred on coastal districts and adjacent ranges of eastern NSW. Fires that broke out on Christmas Eve continued to burn through the first week of January 2002, destroying over 170 homes (Figure 1.8). Hot temperatures were also recorded for eastern Queensland, with many places having their hottest Christmas-New Year period since 1903. Townsville’s record highest December minimum temperature of 28.1ºC was broken four times in the week between Christmas and New Year, while widespread coral bleaching on the Great Barrier Reef was reported.

For 2001 as a whole, rainfall was well above normal over the western two-thirds of the continent with a very wet 2000-01 summer in the north and west. Much of eastern Australia by way of contrast experienced a relatively dry 2001, and the southwestern corner was particularly dry, with record low autumn and early winter rains. For the third consecutive year Australia as a whole had close to normal temperatures: the east of the continent was generally warmer than normal while, over central and western parts, the wet conditions were accompanied by lower than normal temperatures in 2001.

The year 2002 commenced with generally normal to cooler than normal maximum temperatures over most of the continent and rainfall generally near normal. However, February brought Australia’s most intense tropical cyclone of the year. Tropical Cyclone Chris, which briefly reached Category 5 intensity with wind gusts to 290km/h, crossed the coast 160km north east of Port Hedland (Western Australia) on 6 February, bringing some record rainfall totals and local flooding. By March, warm sea surface temperature conditions had developed in the central equatorial Pacific and atmospheric pressure was anomalously high over the western half of the continent, with rainfall deficiencies over large regions. By mid-June the patterns of tropical convection and persistent westerly wind anomalies, combined with the Pacific Ocean temperature signal, confirmed that El Niño conditions had become established. These conditions persisted through the remainder of 2002 and into 2003, as evident in the consistent negative values of the Southern Oscillation Index (SOI - a measure of the atmospheric pressure gradient between the central Pacific Ocean and East Asia) (Figure 1.6).

Figure 1.6 Monthly Southern Oscillation Index (SOI) values since January 1997 associated with the transition from El Niño (1997/98) to La Niña (1998/2001) and back again.

Below normal rainfall continued throughout 2002 for much of Australia as a consequence of the El Niño event. The exceptionally dry March-December period saw 97% of the Australian continent experience below median rainfall, with 61% of the country in the lowest 10% of recorded totals (i.e. decile 1; see Figure 1.7). This was the second largest extent of decile 1 rainfall for any 10-month period on record, only marginally smaller than the decile 1 area of the 1901/02 "Federation Drought" at its peak. It is worth noting, however, that the peak Federation Drought period saw only 78% of the continent below median; compared to the 97% for the 2002 dry event.

Figure 1.7 Rainfall for the 10-month period from March 2002 through to December 2002, showing the widespread rainfall deficiencies associated with the 2002 El Niño event. Only the western half of Tasmania and isolated areas in the Pilbara region of Western Australia recorded above average totals.

The total rainfall for 2002 averaged over Australia was 340mm, well below the longterm average of 472mm, and the 4th driest since 1900, behind 1902 (317mm), 1905 (320mm) and 1961 (336mm). Such long term and widespread dry conditions translated into many local severe rainfall deficiencies. The lowest rainfall total recorded in 2002 was 21.8mm at Muloorina, north of Marree in South Australia, with notably other low totals representing approximately 10-20% of their normal annual rainfall. Winton, in Queensland, recorded only 13% of normal rainfall. In a stark example of the effects of El Niño versus La Niña on rainfall over Australia, only two years earlier, during the extended 1998-2001 period of La Niña conditions, Winton received 1171mm, or 283% of its annual mean rainfall.

The impact of these rainfall deficiencies on the development of drought conditions was exacerbated by high evaporation rates in response to the very high daytime temperatures during 2002. The Australia-wide mean maximum temperatures were the highest on record for autumn, winter and spring. (Seasonal Australia-wide mean temperature records are currently only available from 1950). In all seasons, the previous record was surpassed by a considerable margin. The three seasons (nine months) from March to November saw an all- Australia maximum temperature anomaly of +1.6°C, eclipsing the previous March to November record set in 1980 by 0.6°C (Figure 1.8). The full 2002 maximum temperature anomaly of +1.2°C was also 0.3°C warmer than the previous record (1980). The Australia-wide high maximum temperatures recorded during the year came about as a combination of the warmer than average temperatures of an El Niño event overlying a longer term warming trend. Taken as a whole, there is little doubt that the 2002-03 El Niño event was associated with one of the worst meteorological and hydrological droughts in Australia’s recorded history, despite the fact that on the basis of many of its other meteorological and oceanographic characteristics the event has been classed as moderate.

Figure 1.8 All-Australia rainfall and temperature anomaly time series for the 3-season (9-month) period March to November, 1900-2002, highlighting the very low rainfall and very high maximum temperatures recorded during 2002.

Reduced cloudiness over the continent during 2002 also allowed greater heat loss to space overnight, countering the higher than normal day temperatures, and hence minimum temperatures were much closer to normal. Interestingly, however, the minimum temperatures were considerably higher than those observed in previous strong El Niño drought years (e.g. 1982 and 1994), again reflecting the long-term warming trend.

Figure 1.9 The dust storm of October 2002 extended 1500km long, 400km wide and 2.5km deep as it traversed eastern Australia during a period of extreme drought.

Impacts of the hot and dry conditions were numerous. Dust-storms became prevalent over the interior, with one massive dust storm reaching Sydney and Brisbane on the 23 October (Figure 1.9). Large and devastating bushfires occurred in Queensland, New South Wales, Victoria, the Australian Capital Territory and Western Australia. Water restrictions and reduced irrigation allocations were introduced in many areas. Melbourne introduced water restrictions for the first time since 1982, whilst the nation’s capital, Canberra, saw its first restrictions since 1966. Many areas of the country were declared drought stricken and agriculture and associated businesses were greatly affected. Australian Bureau of Statistics projections, based upon Australian Bureau of Agricultural and Resource Economics forecasts, suggested the cut in total value of agricultural production would be approximately $5 billion for the 2002-03 financial year.