National Water Account 2019

Daly: Climate and water

  • Total annual rainfall was below average and the lowest since the 1991–92 year.
  • The relatively poor rainfall during the wet season resulted in very low flows in the Daly River.
  • Groundwater levels at 30 June 2019 were very low and equivalent to levels usually observed late in the dry season.


 

For further information on the region's climate and water conditions during the 2018–19 year scroll down this page or click on the links below:

 

About the region

  • The Daly region lies within the wet–dry tropics of northern Australia. Almost all rainfall in the region occurs during the wet season (November–April). As a consequence, flow in the rivers is strongly seasonal.
  • Although most of the annual flow in the region's rivers occurs during the wet season, the Daly River system is one of the few in northern Australia to have perennial flow. The dry-season flow (May–October) is mostly dominated by input of groundwater from the two underlying aquifers—Tindall Limestone and Oolloo Dolostone.

 

Climate conditions

Rainfall

Figure C1 Annual and monthly rainfall deciles for the Daly region during the 2018–19 year

 

  • Total area-averaged rainfall for the year was 788 mm, well below the mean value of 1,001 mm.
  • The 2018–19 annual rainfall was the region's lowest since the 1991–92 year.
  • Annual rainfall was below average across almost the entire region. Large tropical low events that typically bring most of the rainfall to the region did not occur during the year.
  • Rainfall was above average in November 2018 due to seasonal thunderstorm activity at the start of the wet season. Above-average rainfall also occurred in April 2019 due to a late monsoon burst at the end of the wet season.

 


Figure C2 Total monthly rainfall for the Daly region during the 2018–19 year compared with the average and percentiles for the region

 

  • Rainfall was above average in November 2018 and April–May 2019. All other months had below-average rainfall.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Daly region during the 2018–19 year

 

  • Total area-averaged actual evapotranspiration was average to above average across most of the region.
  • Despite the relatively low water availability and dry conditions across the region, evapotranspiration was higher during the wet season months, particularly November 2018–February 2019. This is likely due to the record high temperatures experienced across the region during the wet season.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Daly region during the 2018–19 year

 

  • Soil moisture in the root zone (0–1 m depth) was below average across the region.
  • Rainfall and soil moisture are typically closely aligned. For example, below-average soil moisture during December 2018–March 2019 is due to the poor rainfall that occurred during these wet season months.
  • The poor soil moisture conditions during the latter part of the 2018 dry season (July–September) can be attributed to the low rainfall that occurred during the latter part of the 2017–18 wet season (see the 2018 Account).
  • More information on soil moisture distribution across the Daly region is available in the Australian Landscape Water Balance.

 

Flow responses

Streamflow

Figure C6  Map of key flow gauging stations along the main rivers within the Daly region
Figure C6 Key flow gauging stations along the main rivers within the Daly region

 

  • The Katherine and Daly rivers are two primary rivers within the Daly region.

 


Figure C7 Total monthly flow for major rivers in the Daly region during the 2018–19 year compared with average and percentiles

 

  • Total annual flows in the region's major rivers were well below average. For example, total annual flow in the Daly River at Mount Nancar (Station G8140040) was 1,900 GL compared to the average value of 7,386 GL.
  • Total annual flows in the Katherine and Daly rivers were the lowest in more than 25 years.
  • Streamflow in the Katherine and Daly rivers was particularly low during the typically wetter months between January–March, reflecting the poor rainfall conditions across the region for most of the wet season (see Climate conditions).

 

Groundwater level

  • The Tindall Limestone and Oolloo Dolostone aquifers are important groundwater stores providing dry season flow for parts of the river system. The aquifers are also a primary source of consumptive water supply.
  • A key groundwater level monitoring bore for the Tindall Limestone Aquifer is located near Katherine; a key bore for the Oolloo Dolostone Aquifer is located near the junction of the Douglas and Daly rivers.

 

 


Figure C8 Groundwater level in key bores within the Daly region from 2014–2019

 

  • The normal increase in groundwater levels during the wet season in the Tindall Limestone and Oolloo Dolostone aquifers did not occur in 2018–19 due to the poor rainfall conditions across the region during most of the year.
  • Except for a few minor increases in groundwater levels following rainfall events, levels in both aquifers declined for most of the year.
  • Groundwater levels at 30 June 2019 were equivalent to those typically observed late in the dry season during November–December. In the Tindall Limestone Aquifer, end of year groundwater levels were the lowest in more than 20 years (see the Bureau's Groundwater Explorer).