Daly: Climate and water

For the water account period 01 July 2022 - 30 June 2023

  • Total annual rainfall was above average with 2022-23 being the eighth wettest year on record and the wettest since 2010-11.
  • Soil moisture in the root zone (0-1m depth) was above average for most of the region due to the above average wet season rainfall.
  • Total annual streamflows were above average in the Daly River, but below average in the Katherine River despite above average rainfall during the 2022-23 wet season.
  • High recharge rates resulted in an increase in groundwater levels for 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 2022-23 year scroll down this page or click on the links below:

 

About the region

  • The Daly region has a tropical climate, characterised by a hot and humid summers, and warm and dry winters.
  • Almost all of the region's rainfall occurs during the northern Australian wet season (October to April).
  • Although most of the annual flow occurs during the wet season (October to April), the Daly River system is one of the few in northern Australia to have perennial flow. The dry season flow is mostly dominated by input from the two underlying groundwater aquifers (Tindall Limestone and Oolloo Dolostone).

 

Climate conditions

Rainfall

Figure C1 Annual and monthly rainfall deciles for the Daly region during the 2022-23 year

  • Total area-averaged rainfall for the 2022-23 year was 1,414 mm, 37% above the mean value of 1,035 mm. It was the region's eighth wettest year and wettest September to November period on record.
  • Though typically dry, an unseasonable rainband during July 2022 resulted in the fourth wettest July on record for the area.
  • In September 2022, a third consecutive La Niña event was declared active in the tropical Pacific Ocean and remained active through to March 2023. La Niña events tend to increase the chance of above-average rainfall during the northern wet season.
  • A relatively wet September and October saw an earlier than usual Northern Rainfall Onset (defined as the date when the cumulative rainfall after the 1st of September reaches 50mm and considered to be the approximate amount of rainfall required to stimulate plant growth).
  • Widespread storm activity and monsoonal bursts contributed to much higher than average rainfall during the wet season. In late December, Tropical Cyclone Ellie crossed the coast just south of the mouth of the Daly River and delivered heavy rainfall over subsequent days as a slow moving tropical low. 
  • February had the highest rainfall (nearly 60% above average) due to monsoon bursts associated with the strong Madden-Julian Oscillation (MJO) activity in the tropical Australian region.
  • The 2022-23 wet season was the region's eighth wettest on record, contributing to 97% of the region's total area-averaged rainfall for the 2022-23 year. More information on Australia's 2022-23 Northern Wet Season can be found at: Australia's 2022-23 Northern Wet Season.
  • Following the end of the 2022-23 wet season, little rainfall was recorded over the region during May 2023 and June 2023 which is typical for this time of year.
  • More information on Australia's climate and water over the 2022-23 year can be found at: Financial year climate and water statement 2022-23.

 

Figure C2 Total monthly rainfall for the Daly region during the 2022-23 year compared with the average and percentiles for the region

  • Rainfall was above the 90th percentile in July 2022 due to an unseasonable rainfall event.
  • Further significant rainfall events saw monthly totals for October 2022, November 2022, December 2022, and February 2022 equalling or peaking above the 90th percentile.
  • August 2022, May 2023, and June 2023 all recorded less than 1 mm (10th percentile), however very low rainfall is typical during the dry season months.

 

Actual evapotranspiration

Figure C3 Annual and monthly actual evapotranspiration deciles for the Daly region during the 2022-23 year

  • Total area averaged actual evapotranspiration for the 2022-23 was predominantly above average, with high wet season rainfall increasing water availability.
  • Unseasonable rainfall during July 2022 led to evapotranspiration being above average across this area, except for the northeastern corner which missed out on the rain.
  • A very warm and wet October saw much above average evapotranspiration at the onset of the wet season, particularly across the northern half of the region.
  • Evapotranspiration remained above average throughout the wet season, with high rainfall totals from the remnants of Tropical Cyclone Ellie in late December and monsoonal bursts in late January 2023 and February 2023 maintaining high water availability.
  • Despite May 2023 and June 2023 being dry, evapotranspiration was mostly average to above average through to the end of the 2022-23 year.

 

Soil moisture

Figure C4 Annual and monthly soil moisture deciles for the Daly region during the 2022-23 year

  • Soil moisture in the root zone (0–1 m depth) for the 2022-23 year was above average for most of the region, except for a small pocket in the northeast.
  • Unseasonable rainfall during July 2022 resulted in very much above average soil moisture, with much of the northwest experiencing highest July soil moisture on record.
  • Significant rainfall from storm activity, several monsoonal bursts and the remnants of Tropical Cyclone Ellie helped maintain predominantly above average soil moisture conditions in the lead up to and throughout the wet season.
  • Despite very little rainfall going into the 2023 dry season, soil moisture remained average to above average through to the end of June 2023.
  • 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 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.
  • During the dry season, minimum flows in the Daly River and Katherine River are maintained by groundwater discharge from the region's aquifers.

 

Figure C7 Total monthly flow for major rivers in the Daly region during the 2022-23 year compared with the average and percentiles

  • Total annual flow in the Daly River at Mount Nancar (Station G8140040) was above average, but despite the region overall having its eighth wettest wet season on record, total annual flow in the Katherine River at Railway Bridge (Station G8140001) was below average.
  • Streamflows in both sites remained at base flow levels during the lead up to the wet season, however, heavy rainfall events from October saw flows rise toward the end of 2022.
  • Following high rainfall from monsoonal bursts over the catchment area, streamflow peaked above average in February in the Katherine River and well above average in March at the Daly River gauge further downstream.
  • Streamflows in both rivers had returned to base flow volumes by June 2023, as is typical for these river systems.

 

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 2014–2023

  • Groundwater levels in the Tindall Limestone and Oolloo Dolostone aquifers increased during the 2022-23 year with above average wet season rainfall increasing recharge.
  • A monsoonal burst from late February to early March brought storms and heavy rain to the region resulting in the water level in both aquifers rising by around 3m during this period.
  • Following the end of the 2022-23 wet season, levels steadily dropped through to the end of June 2023.
  • By June 30, 2022 the Tindall Limestone aquifer finished 1.18m higher than that time last year, while the Oolloo Dolostone aquifer finished 1.88m higher compared to the same point in the previous year.
  • More information on Daly's groundwater resources can be found in the Region description.

Note: Data at the Oolloo Dolostone Aquifer was only available until the 15th of March, 2023