Inland Eastern Australia Droughts

Synopsis: A severe drought is at present (March 2020) affecting the eastern region of Australia, particularly the inland region of northern New South Wales and southern Queensland. An analysis has been made of rainfall data at eight locations with records extending over between 133 and 148 years. The most severe droughts at each location were identified. Droughts (and floods) are a feature of the Australian climate and seven major droughts were identified that were of similar or greater severity than the present drought. The analysis only examined the rainfall data although it is recognised that other factors such as temperature, wind and non-meteorological matters (eg farming practices and the economic situation) may also affect drought severity.

The region covered is west of the coastal range with mean annual rainfalls varying from about 250 mm to 650 mm. The region experiences hot summers and mild (in the north) or cool (in the south) winters. In the north much of the rainfall occurs, on average, during the summer months but in the south it is more evenly distributed throughout the year.

The area covered by the analysis is huge with a North-South dimension of about 1,500 km and an East-West dimension of about 800 km.

DATA USED

Monthly rainfall data at eight long-term stations were obtained from the website of the Australian Bureau of Meteorology http://www.bom.gov.au/climate/data/ The latest data used were for December 2019.

DETAILED ANALYSES

Detailed analyses have been made for the eight individual locations and are only summarised here. Links to these analyses are listed below.

Drought Intensity. Rainfall totals were extracted for five periods (12, 24, 36, 48 and 60 months) continuously over the full records. These totals were ranked to determine the dates with minimum (drought) rainfalls. The rainfalls identified are for the period up to the specified date. The five most intense droughts were identified for each period.

Drought Duration. For the purpose of these analyses a drought was deemed to have occurred if the x-month preceding rainfall (ie the total rainfall for the preceding x months (x = 12, 24, 36, 48 or 60)) was less than the mean annual minimum value. The five longest droughts were identified for each period.

REGIONAL COMPARISONS

The individual analyses identified seven major droughts that had occurred at one or more location. The duration of these droughts varied with the period analysed (12 to 60 months) and the individual location, so the following dates are indicative only: 1880-1887, 1895-1906 (or 1895-1918), 1922-1950, 1962-1973, 1985-1998 (or 1991-1997), 2001-2011 and 2013-2019.

It is seen that all eight locations experienced severe droughts for many of the years 1895-1906 and for many of the following years up to 1950.

Three of the southern locations (Dubbo, Balranald and Tarcutta) were free of major droughts in many of the years 1950-2000. However, the same three locations experienced major droughts in many of the years 1880-1890.

Five of the northern locations (Barcaldine, Miles, Cunnamulla, Collarenebri and Wilcannia) experienced major droughts in many of the years 1962-1973.

Six locations (Miles, Cunnamulla, Collarenebri, Wilcannia, Dubbo and Tarcutta) experienced major droughts in many of the years 2000-2010.

Three locations (Cunnamulla, Collarenebri and Tarcutta) experienced major droughts in many of the years 2013-2019.

The overall time distribution of severe droughts is seen in the following figure which shows the approximate number of severe droughts in each decade extending over three or more years.

EXAMPLES OF DROUGHT GRAPHICS

Examples of 12, 36 and 60 month droughts at three locations (Barcaldine, Dubbo, Balranald) are as follows:

 

LINKS TO DETAILED ANALYSES

Links to the detailed analyses at the eight individual locations are:

Barcaldine              Miles               Cunnamulla             Collarenebri    

Wilcannia               Dubbo            Balranald                   Tarcutta

 

COMMENTS

Seven major droughts were identified to have occurred in the inland New South Wales and Queensland over the 140 years since 1880. Some of these droughts affected only part of the region.

The duration of the droughts varied depending on the period (12-60 months) being analysed, but the indicative enveloping dates of the seven major droughts identified are: 1880-1887, 1895-1906 (or 1895-1918), 1922-1950, 1962-1973, 1985-1998 (or 1991-1997), 2001-2011 and 2013-2019.

Many of the droughts extended over many years. The “Federation Drought”, approximately 1895-1906, affected the whole of the study area.

Apart from the years 1950-1960 and 1975-2000 major droughts have occurred throughout the study area since 1880.

The current drought, which commenced in about 2013, was still continuing up to December 2019 and in many cases is comparable in severity to several historic droughts.

The analysis involves the study of only rainfall data. Although rainfall is the primary factor affecting the severity of droughts, other meteorological factors (such as temperature, wind and humidity) and non-meteorological factors (such as farming practices and economic conditions) also affect the severity of droughts. Even with rainfall, the drought effect will be different depending on the seasonal distribution and intensity of rainfall.

The severity of a drought has different significance for different situations. For example, the different impact of a given drought on dry-land livestock farmers, irrigation farmers, town water supplies, horticulturists or environmental interests.

 

POSTSCRIPT

During January and February 2020 there was rainfall throughout the study are, but were probably insufficient to end the present drought. The largest rainfalls (Jan/Feb) were at Miles (76/192 mm) and Collarenebri (83/191 mm).

 

Please let me know what you think of my analysis.
brigun (at) westnet.com.au

 

The Author:

   This article was written by Brian Gunter of Narooma, NSW, Australia. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.