Daly: Climate and water
- Total annual rainfall was well below average and the lowest since the 1963–64 year.
- Streamflows were very low in the Daly River for the second consecutive year.
- Groundwater levels at 30 June 2020 were at their lowest levels in more than 20 years.
For further information on the region's climate and water conditions during the 2019–20 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 2019–20 year
- Total area-averaged rainfall for the year was 714 mm, well below the mean value of 1,034 mm, and the region's lowest in more than 50 years.
- The transition of the Southwest Indian Monsoon into the southern hemisphere was six weeks later than average and the latest on record. The delayed monsoon period meant very little rainfall occurred across the region at the start of the 2019–20 wet season, which contributed to the below-average annual rainfall.
- This was the region's second consecutive year of well below-average wet season rainfall. Over the last two years, the region has experienced its driest 24-month period since 1960–62.
- Thunderstorms and showers during early-April 2020 contributed to the above-average rainfall for that month.
Figure C2 Total monthly rainfall for the Daly region during the 2019–20 year compared with the average and percentiles for the region
- Rainfall was close to average in February 2020 and slightly above average during April–May 2020. All other months had below-average rainfall.
- Heavy rainfall associated with ex-tropical cyclone Esther, which impacted the region in late February 2020, contributed to the higher rainfall for that month.
Actual evapotranspiration
Figure C3 Annual and monthly actual evapotranspiration deciles for the Daly region during the 2019–20 year
- Total area-averaged actual evapotranspiration was below average across most of the region.
- Evapotranspiration was well below average during the early part of the wet season (October–January) due to low water availability following the delayed onset of the 2019–20 monsoon period.
- Evapotranspiration was above average over large parts of the region during February–March 2020 following heavy rainfall associated with ex-tropical cyclone Esther, which impacted the region in late February 2020.
Soil moisture
Figure C4 Annual and monthly soil moisture deciles for the Daly region during the 2019–20 year
- Soil moisture in the root zone (0–1 m depth) was well below average across most of the region.
- The delayed monsoon period meant very little rainfall occurred at the start of the 2019–20 wet season. By December 2019, root-zone soil moisture was well below-average and lowest on record in the eastern part of the region.
- Soil moisture was near average during March–April 2020 following higher rainfall in the latter part of the wet season.
- More information on soil moisture distribution across the Daly region is available in the Australian Landscape Water Balance.
Flow responses
Streamflow
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 2019–20 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 2,329 GL compared to the average value of 7,156 GL. Streamflow in the Katherine River was the lowest in 30 years.
- This was the second consecutive year of very low flows in the Katherine and Daly rivers.
- Streamflow in the Katherine and Daly rivers was particularly low during the first part of the wet season (November–January) reflecting the poor rainfall conditions during these months due to the delayed onset of the monsoon period (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 2014–2020
- For the second consecutive year, the normal increase in groundwater levels during the wet season in the Tindall Limestone and Oolloo Dolostone aquifers did not occur due to poor wet season rainfall.
- Except for a few minor increases in groundwater levels following rainfall events, levels in both aquifers declined for most of the year.
- At 30 June 2020, groundwater levels in the Tindall Limestone Aquifer were the lowest in more than 20 years; levels in the Oolloo Dolostone Aquifer were the lowest on record (since 2006).