Daly: Climate and water

  • Total annual rainfall for the 2021–22 year was below average following a poor wet season.
  • Streamflows were below average for most of the year.
  • Groundwater levels decreased in both the Tindall Limestone and Oolloo Dolostone aquifers.

Schematic representation of the Daly region. In 2021–22, rainfall was 902 mm, below average. Streamflow in Daly River in 2021–22 was 7,143 GL compared to the average value of 3,956 GL. Groundwater levels decreased by more than 2 metres.

For further information on the region's climate and water conditions during the 2021-22 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 2021–22 year

  • Area averaged rainfall for the 2021-22 year was 902 mm, 13% below the annual mean of 1,036 mm.
  • In July 2021, a negative Indian Ocean Dipole (IOD) event was declared and remained active until December 2021, while a La Niña was active between November 2021 and April 2022. Both a negative IOD and La Niña tend to enhance rainfall across the region.
  • Area averaged pre-wet season rainfall (July to October 2021) was around 50mm in total, about 30% above average for this time of year.
  • Tropical Cyclone Seth brought heavy rainfall over the Top End in late December.
  • There were only four significant periods of monsoon activity: early-November 2021, late-December 2021, mid-January 2022, and late-April 2022, with only December 2021 and April 2022 recording above-average rainfall.
  • More information on Australia's climate and water over the 2021-22 year can be found at: Financial year climate and water statement 2021-22.

 

Figure C2 Total monthly rainfall for the Daly region during the 2021–22 year compared with the average and percentiles for the region

  • Pre-wet season rainfall (July to October 2022) was 30% above average.
  • A lack of monsoonal activity resulted in below average rainfall for the 2021-22 wet season. 
  • December 2021 and April 2022 recorded above average rainfall.
  • February and March were significantly drier than average (close to the 10th percentile for rainfall).

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Daly region during the 2021–22 year

  • Total area averaged actual evapotranspiration was above average in the western half and below average in the eastern half of the region during the 2021-22 year.
  • Evapotranspiration was average to above average over most of the region in the months leading up to the 2021-22 wet season (July to October 2021) and remained above average into the start of the wet season (November 2021 to February 2022) with higher water availability from early season rainfall events.
  • From March to June 2022, evapotranspiration decreased to below average, particularly in the northeastern corner of the region, due to low monsoonal activity and the associated reduction in water availability.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Daly region during the 2021–22 year

  • Soil moisture in the root zone (0–1 m depth) was predominantly average to below average during the 2021-22 year.
  • By the start of the 2021-22 wet season, soil moisture was average to above average across the region following above average rainfall during October 2021.
  • Monsoonal bursts in early-November, late-December, and mid-January maintained average to above average soil moisture from November 2021 to January 2022.
  • From February 2022 onwards, a lack of rainfall events resulted in soil moisture drying significantly and remaining below average to very much below average through to the end of the 2021-22 year. The northeast was particularly dry, with some areas experiencing their lowest soil moisture on record from March to May 2022.
  • More information on soil moisture distribution across the Daly region is available in the Australian Water Outlook.

 

Flow responses

Streamflow

Map of key gauging stations. Katherine River at the Railway Bridge, station number G8140001, in the central part of the region near Katherine. Daly River at Mount Nancar, station number G8140040, in the region's northwest near Nauiyu.
Figure C5 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 C6 Total monthly flow for major rivers in the Daly region during the 2021–22 year compared with the average and percentiles

  • Total annual flows in the region's major rivers were below average, reflecting the below-average rainfall during the 2021-22 season.
  • For example, total annual flow in the Daly River at Mount Nancar (station G8140040) was 3,956 GL compared to the annual average of 7,942 GL, around 50% below the annual average. Total annual flow in the Katherine River at the Railway Bridge (Station G8140001) was also about 50% below the annual average.
  • Streamflows peaked in January 2022 following heavier rainfall events in late December and mid-January. 
  • Without further significant rainfall in the catchment areas, streamflows were below average for the remainder of the 2021-22 wet season and into the 2022 dry season.

 

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 C7 Groundwater level in key bores within the Daly region from 2014–2022

  • At 30 June 2022, groundwater levels in the Tindall Limestone and Oolloo Dolostone aquifers were below the observed levels at the same time last year due to below average rainfall during the wet season.
  • Groundwater levels at the Tindall Limestone and Oolloo Dolostone aquifers decreased by almost two metres from July 2021 to January 2022.
  • Following a monsoonal burst in mid-January, both aquifers rebounded by at least one metre over the next four to six weeks, peaking in late-February 2022.
  • Without further significant recharge events from March 2022 onwards, the water level decreased in both aquifers, finishing the 2021-22 year 2.49 metres lower than last year.

Note: Data at the Oolloo Dolostone Aquifer was only available until the 14th of March, 2023