New South Wales Monthly Climate Summary: October 2006
Hottest and driest October on record

Wednesday 1 November, 2006

In Brief

Main points:

• Hottest October on record for statewide average maximum temperatures
• 60 of the past 70 months have seen above average maximum temperatures across the state
• Above average minimum temperatures over large areas, especially in the north and west
• Below average minimum temperatures in the south east
• Driest October on record for NSW exceeding that of the 2002 El Niño and 1900 Federation Droughts
• Driest October on record for the Murray Darling Basin which received only half the rainfall of the previous driest October on record (Federation drought - 1900)
• 6th driest of any month on record for Murray Darling Basin (records since 1900)
  

October 2006

Temperatures:

October 2006 was by far the hottest October on record for NSW with the statewide average maximum temperature more than 3.2ºC above the historical average¹of 24.4ºC (records since 1950). A vast area stretching from the Upper Western to the ACT and Riverina experienced the hottest October maximum temperatures on record (Figure 1). The greatest departures from average temperatures were in the central and southern slopes of the Great Divide and into the Riverina. In these areas temperatures were more than 5 degrees above the October average (Figure 2).

On several days during October strong hot and dry NW winds from the interior of the continent pushed across NSW. Many new daily maximum temperature records were set across the state, especially in the period 13−14 October (see records table below). Early bushfires broke out across the state on these days of extreme fire danger.

The extraordinary heat of this past month is also part of a longer sequence of above average maximum temperatures affecting the state. In the past 70 months 60 have been above the historic average for statewide maximum temperatures. Twelve of the last 24 months have been ranked in the top 10 warmest of their respective calendar month and 4 were the warmest ever recorded since statewide area averaged records began in 1950.  Of the last 24 months only 3 have been cooler than average across the state. Whilst 2002 and 2006 temperatures have been enhanced by El Niño events the exceptional warmth through the entire period (2001−2006) is consistent with global rising temperatures due to anthropogenic climate change.

Minimum temperatures were also above average in the north west of the state with the statewide average temperature more than 0.7ºC above the historical average of 10.5ºC. The far north west of the state and an area around Cobar experienced the warmest October nights on record. In contrast the southeast of the state experienced below average minimum temperatures during October (Figure 3). The area of below average minimum temperatures also extended north to the Central Coast. The colder than average nights in the southeast were caused by frequent dry cool southerly changes pushing along the border and north along the coast from Victoria. Without the commonly associated cloud cover these wind changes merely enhanced diurnal cooling and allowed overnight temperatures to fall below the October average. In some alpine areas new lowest October daily minimum records have been set (see records table below).

Rainfall:

NSW recorded its lowest statewide averaged October rainfall on record (records since 1900). Only 6.6 mm fell across the state compared to the October average of 48.9 mm. This monthly total is lower than that of the 2002 drought (8.0 mm) and even lower than that of the Federation Drought year 1900 (7.0 mm). Conditions in the Murray Darling Basin (MDB) were particularly severe during October. The MDB recorded its lowest October rainfall on record with an average of only 3.2 mm compared to the October average of 44.0 mm. The October rainfall in the MDB was half that of previous driest October in the Federation Drought year 1900 (6.9 mm). This October also ranks at the 6th driest of any month on record for the MDB.

Large tracts of southern NSW experienced lowest October rainfall totals on record. Almost the entire state recorded below to very much below average falls. Only the far north west and areas of the Mid North Coast and Northern Rivers received close to average monthly rainfall (Figure 4). Very much below average rainfall across NSW is expected during El Niño events. This impact of this El Niño event is exceptionally severe with large areas of the eastern half of the continent experiencing lowest October rainfall on record (Figure 5).

The extraordinarily dry month of October is a continuation of the El Niño induced drought which began across much of the state in February. Almost the entire state has received below average falls during this period with the southeast worst affected. A large area encompassing the central and southern slopes of the Great Divide has received lowest February to October totals on record (Figure 6). The extreme dry of this year is also an extension of a protracted dry period which has affected the state since 2001.