NSW State Seasonal Update - September 2021

Prepared by NSW DPI

NSW overview

Average to above average rainfall continues to support a strong Spring 2021 production outlook across much of NSW. The NSW DPI Combined Drought Indicator (CDI) shows 88% of NSW in the Recovery or Non-Drought categories at the end of September. The seasonal rainfall outlook indicates high chances of above median rainfall across NSW for the next three months.

Despite the strong overall outlook Western NSW and western areas of the Riverina and Murray regions continue to experience a slow, variable and delayed drought recovery. The North Coast region has also experienced a dry period since substantial rain in March. In contrast the risk of waterlogging in paddocks and localised flooding remain in some regions due to high levels of soil moisture, particularly the slopes, central and tableland districts.

The 2021 winter crop yield potential remains high however conditions are variable across the grain belt. The irrigated crop forecast for the 2021-22 season is high due to high soil moisture levels and water availability in the state’s reservoir and irrigation schemes. Water availability has increased and is expected to support a strong irrigated crop forecast for the 2021-22 season. While the main winter frost season is now over volatile spring weather brings the risk of out of season frost events. This is at a time when the cereal crops sown in NSW during 2021 are more vulnerable to yield damage.

Pasture growth and livestock productivity remain high across most of NSW due to recent rainfall and high soil moisture levels. Warmer spring temperatures will accelerate pasture growth at higher altitudes in the new few weeks. In many districts the nutritional value of pasture for livestock will start to plateau then decline as the temperatures warm.

The latest Bureau of Meteorology (BoM) Seasonal Outlook indicates high chances of above median rainfall across NSW for the three months between October and December. The ENSO Outlook status is currently at La Niña Watch. A negative Indian Ocean Dipole (IOD) event has weakened since the August Update. A negative IOD event typically increases the chance of above median winter and spring rainfall across south-eastern Australia. Pacific Ocean sea-surface indicators remain in a neutral state.

The CDI and its individual rainfall, soil moisture and crop/pasture growth metrics are leading biophysical indices of drought. Factors affecting production and economic responses usually lag the CDI. Further information about the correct interpretation of the CDI at a region and industry level is provided in the regional breakdown section of this report.

It is important to recognise the CDI provides an aggregated view of the State, and that on-ground conditions can be different to those displayed in the maps. They provide an ‘on average’ view of a particular region only. To report local conditions, use DPI Farm Tracker.

Rainfall

The rainfall anomaly data shows the difference between total monthly rainfall and the long-term average (1961-1990; Figure 2a). Most of eastern NSW and parts of western NSW have received average to below average rainfall in September. Central parts of NSW have received average to above average rainfall. The highest rainfall deficits have been recorded in the North Coast, Hunter, Greater Sydney and South East Local Land Services regions.

Rainfall totals were variable across NSW during September (Figure 2b). The highest rainfall totals were received in the eastern parts of the Riverina and Murray LLS regions, and alpine areas in the South East LLS region. Elsewhere rainfall totals ranged between 10-100mm. Parts of the far west received less than 10mm.

Rainfall accumulation during the 2021 calendar year has been near or above average across most of NSW. Most of coastal NSW and the Tablelands areas have received more than 600mm in the year (Figure 2c). Parts of the North Coast and alpine regions have received more than 1400mm during the year. Central areas west of the Great Dividing Range have generally received between 300-600mm, while eastern areas of the Western LLS region have recorded 200-300mm. Much of the far west has received below average rainfall in 2021. Totals have been below 200mm for the year, and below 100mm in areas along the South Australian border.

Temperature

Most of NSW experienced maximum temperature anomalies between 0-2°C during September (Figure 3a). The average September maximum temperatures were generally above 15°C across NSW, with cooler temperatures in the Central Tablelands and Alpine regions (Figure 3b). Much of northern NSW received maximum temperatures ranging between 21-27°C.

Minimum temperatures were near average across most of NSW in September. Some parts of central NSW were up to 3°C below long term average (Figure 3c). Mean minimum temperatures ranged between 3-12°C across most of the state (Figure 3d). Tablelands and Alpine regions at higher altitudes experienced cooler temperatures between -3 to 3°C.

The frost days map (Figure 3e), shows the number of days that minimum temperatures were less than 0°C across the state in September. The number of frost days has reduced compared to winter months.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 4) indicates that plant greenness levels are close to, or above normal across most of NSW for the July to September period. Lower than normal plant greenness remains evident across large areas of the Western LLS and western areas of the Riverina and Murray LLS regions. Some areas affected by the 2019/20 bushfires also remain evident in the Central Tablelands, Northern NSW and South East.

NSW Farm Dam Survey

The NSW Farm Dam Survey indicates large areas of south-western and western NSW have farm dam levels less than 20% of capacity (Figure 5). Dam levels are generally greater than 40% of capacity across eastern areas of the state. Large areas in central, central northern and the southern slopes areas have dam capacities greater than 80%.  There have been modest improvements to conditions in the eastern Riverina and Murray regions, while coastal regions have seen slight reductions in capacities.

Soil Water Index

The Soil Water Index (SWI, Figure 6) indicates the majority of NSW is currently in the average to above average categories. Parts of western and south-western NSW were in the below average category, as well as small areas in the North Coast and South East LLS regions.

Plant Growth Index

The Plant Growth Index (PGI, Figure 7) indicates that the majority of NSW is in the average to above average categories at the end of September. Parts of south-western, western and the North Coast and Hunter regions were in the below average category. There is an area north of Broken Hill in the extremely low PGI category.

Rainfall Index

The Rainfall Index (RI, Figure 8) indicates that the majority of NSW is currently in the average to extremely high category. This reflects the distribution of average or above rainfall that has been accumulated rainfall over the last 12 months. Western parts of the Murray LLS region are in the below average category.

Drought Direction Index

The Drought Direction Index (DDI, Figure 9) tracks the 150-day trend of daily rainfall totals. The DDI indicates much of NSW is in a neutral to drying trend. The DDI is tracking a strong drying trend along coastal NSW, highlighting the presence of a short-term rainfall deficit in these districts.

Changes in the individual drought indicators may have occurred since this update was released. For the most current information, please visit DroughtHub.

CDI status for the regions

Figure 10 displays the CDI status for each individual Local Land Services region to 30 September 2021. The following regional descriptions are based on data available until the end of September 2021.

Murray and Riverina regions

The Combined Drought Indicator (CDI; Figure 11) shows a large area in the west of the Riverina and Murray Local Land Services (LLS) regions remains in the Drought Affected category at the end of September. Follow-up rain is needed to lift longer-term confidence of drought recovery and spring rainfall is a key focus prior to the onset of hot summer conditions later in the year. Rainfall and agronomic conditions further east underpin a strong seasonal outlook.

The seasonal NDVI anomaly data (Figure 12) shows that most of the Murray and Riverina regions were experiencing near to or higher than normal plant greenness levels for the July to September period. Plant greenness levels remain lower than expected in western areas of the Murray and Riverina LLS regions. The impact of the 2019/2020 bush fires is still evident south of Tumut.

The time series charts (Figure 13) show the individual response of the drought indices for Hay, Finley, Temora and Moulamein. Temora and Finley remain steady with average to high soil water, plant growth and rainfall indices. Further rainfall is required at Hay and Moulamein to improve conditions. Variable, weak or delayed drought recovery has occurred in these areas compared to other locations due to lower rainfall during 2020/21.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months and shows how the indices are tracking compared to long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

Western region

The Combined Drought Indicator (CDI; Figure 14) shows that drought conditions are variable across the region. While much of the region is in the Non-Drought or Recovering CDI category, the area in the Drought Affected category has expanded since the August State Seasonal Update. The agronomic indicators of the CDI remain at low levels across many parts of the Western LLS, highlighting the need for consistent follow-up rain. The DPI continues to monitor conditions closely across the Western LLS.

The seasonal NDVI anomaly data (Figure 15) shows variability across the Western LLS region. Much of the region is experiencing near normal or higher levels of plant greenness for the July to September period. Large areas of the far west and south-west have low plant greenness levels, along with parts of central Western LLS near Bourke.

The time series charts (Figure 16) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. Ivanhoe remains in the Non-Drought category with high soil water, plant growth and rainfall indices. Further rainfall is required at Bourke to maintain the Non-Drought status. Wentworth is currently in the Drought Affected category and rainfall in required to improve conditions. NSW continues to monitor the Western LLS region closely.  To access a time series for your Parish, visit the Combined Drought Indicator website.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months. This is then ranked against all other 12-month periods. This shows how the indices are tracking compared to the long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

North West, Northern Tablelands and North Coast regions

Winter and spring rainfall have continued drought recovery across the North West and Northern Tablelands Local Land Service regions. The North Coast LLS region experienced a dry winter, however productive conditions have generally been maintained after large rain totals were received earlier in the year. The Combined Drought Indicator (CDI; Figure 17) shows most of these regions are in the Non-Drought category. The winter rainfall has replenished soil water levels to field capacity in some areas, especially where overland flooding occurred in March. NSW DPI is closely monitoring conditions along parts of the North Coast after an extended dry period.

The seasonal NDVI anomaly data (Figure 18) indicated near to above-normal greenness across most of the regions for the July to September period.

The time series charts (Figure 19) show the individual response of the drought indices for Moree, Walgett, Tenterfield and Lismore. The indicators remain steady at Moree and Tenterfield with high soil water, plant growth and rainfall indices. Walgett and Lismore remain in the Non-Drought category though further rainfall is needed to improve the plant growth and soil water indices.  The NSW DPI continues to monitor the northern regions closely. To access a time series for your Parish, visit the Combined Drought Indicator website.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months and shows how the indices are tracking compared to the long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

Central Tablelands, Central West, Hunter and Greater Sydney regions

Most of the Central West, Central Tablelands, Hunter and Greater Sydney Local Land Services (LLS) regions remained in the Non-Drought CDI category in September (Figure 20). The regions remain in a strong position for 2021 Spring production, with high soil water levels in many areas. Parts of the Hunter LLS have experienced a comparatively drier winter  and have transitioned in the Drought Affected category. The NSW DPI continues to monitor the region closely.

The seasonal NDVI anomaly data (Figure 21) shows near normal to high levels of plant greenness across most of the LLS regions for the July to September period. The 2019/20 bushfire impact is still evident in parts of the Central Tablelands, lower Hunter and west of Greater Sydney.

The time series charts (Figure 22) show the individual response of the drought indices for Cowra, Condobolin and Singleton. Follow-up rainfall has supported the CDI indicators at all locations and there is evidence of a strong drought recovery. These regions currently remain well placed for productive conditions in 2021, though drier September conditions did cause the indicators to fall at Condobolin and Singleton.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months. and shows how the indices are tracking compared to the long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

South East region

The Combined Drought Indicator (CDI; Figure 23) shows that most of the South East Local Land Services region is in the Non-Drought CDI category. Overall, the South East LLS region remains well positioned for a productive 2021 Spring period. However, the CDI shows that an area around Nowra is currently in the Drought Affected category and there are signs of short term drying in coastal districts. It is important to continue monitoring conditions in this region.

The seasonal NDVI anomaly data (Figure 24) showed near normal to high levels of plant greenness across most of the region for the June to September period. The areas impacted by the 2019/20 bushfires continue to have lower than average plant greenness levels.

The time series charts (Figure 25) show the individual response of the drought indices at Bega, Goulburn and Cooma. The three regions remain in the Non-Drought category high soil water, plant growth and rainfall indices. These regions currently remain well placed for productive conditions in 2021.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months and shows how the indices are tracking compared to the long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

Official national outlook

The official national outlook was released by the Bureau of Meteorology (BoM) on 30 September 2021. Rainfall during October to December is likely to be median to above median for most of Australia. Below median rainfall is likely for parts of western Tasmania. Near equal chances of above or below median rainfall is likely for parts of western Australia.

Daytime temperatures are likely to be above median for the northern tropics and the far south-east of Australia. Below median daytime temperatures are likely for southern and central Australia, as well as southern Queensland. Above median minimum temperatures for spring are very likely across Australia, except for parts of southern Western Australia.

The Bureau issues a new 3-month seasonal update weekly, each Thursday afternoon.

NSW outlook

Most of NSW has high chances of receiving above median rainfall between October and December (Figure 26). The daytime temperature outlook indicates moderate chances of cooler than median temperatures across most of NSW (Figure 27). Coastal regions and far south-eastern NSW have a near equal to moderate chance of above median maximum temperatures. There is a moderate to high probability of warmer than median overnight temperatures across the state (Figure 28).

Global climate drivers

El Niño–Southern Oscillation (ENSO)

The Bureau of Meteorology’s (BoM) El Niño-Southern Oscillation (ENSO) Outlook was released on 28 September 2021. The ENSO status remains neutral. Sea surface and sub-surface temperatures have cooled in the central tropical Pacific over recent months. The ENSO outlook is currently at La Niña Watch. Three of the seven models surveyed by the BoM are predicted to meet La Niña thresholds in Spring and remain at values that indicate La Niña state until early 2022. Two other models briefly reach the threshold indicative of a La Niña, but do not persist through to 2022. La Niña typically increases the chance of above median rainfall in NSW during Spring.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 26 September 2021 was +9.3. The 90-day SOI value was +9.4. The 30-day value has maintained similar values for the past fortnight.

Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.

Sea surface temperatures (SST)

Sea surface temperatures (SST) for the tropical Pacific Ocean are currently close to average across much of the equatorial Pacific Ocean. Areas of slightly cooler than average SSTs have increased in the central to eastern equatorial Pacific in the past month, while warmer than average SSTs persist across the far western Pacific.

The latest values of the three NINO indices in the tropical Pacific for the week ending 26 September were: NINO3 -0.4°C, NINO3.4 -0.3°C, NINO4 0.2°C. All three NINO indices are within the ENSO-neutral range.

Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than −0.8 °C typically indicate La Niña.

Sea sub-surface temperatures

Cool sub-sea surface conditions have been building over the last four months, with cool sub-surface anomalies becoming widespread along the equatorial Pacific at the end of September. Sub-surface anomalies reached up to 4ºC cooler than average in the central Pacific at a depth of 150m. Weak warm anomalies are present across parts of the water columns in the western Pacific.

Indian Ocean (IOD)

The negative Indian Ocean Dipole (IOD) event has weakened since the August update. Current values are close to the negative threshold (-0.4ºC). If this continue, it is likely that the negative IOD is near its end. However, persistent warm anomalies in the eastern Indian Ocean are still expected to influence Australian rainfall patterns. The latest weekly value of the Indian Ocean Dipole (IOD) index to 26 September 2021 was −0.29 °C.

A negative IOD event increases the chances of above average winter and spring rainfall for parts of southern Australia.

Southern Ocean (Southern Annular Mode – SAM)

The Southern Annular Mode (SAM) index has been positive for most of September and is forecast to remain positive for the next three weeks. It is likely to remain mostly positive through December due to strengthened westerly winds around Antarctica and the developing La Niña. A positive SAM typically increases the chance of above average rainfall for much of New South Wales during spring and summer.

The Southern Annular Mode (SAM) refers to the north-south shift of rain-bearing westerly winds and weather systems in the Southern Ocean compared to the usual position. This indicator can be quite volatile and generally influences weather conditions on 1-3 week timescales. SAM forecasts are highly uncertain beyond 2-3 weeks.

How does it work?

Much of the information in the Seasonal Conditions Report is sourced from the NSW DPI Enhanced Drought Information System (EDIS) ™. The EDIS system is currently available in prototype form and is subject to an intensive ground truthing process. For more information, visit the interactive website via DroughtHub.

EDIS is an ongoing project aimed at improving the quality and timeliness of efforts to monitor conditions across the state. Key features of the system are:

• It tracks drought by using four indicators; rainfall, soil water, plant growth, as well as tracing rainfall trends. Agronomic conditions have equal value to rainfall recorded at meteorological stations.
• The Combined Drought Indicator (CDI) brings this information together and has been designed to characterise developing drought conditions. The key purpose for building the CDI was as a drought early warning system.
• The rainfall, soil moisture and plant growth indicators in EDIS account for conditions over a 12-month window. This provides a compromise between a highly sensitive indicator (e.g. six months) and a less sensitive indicator (e.g. 24 months).
• Climate and remote sensing data drive the information system at a high resolution, but the CDI is reported at a Parish level.
• Because of its configuration and purpose, there will be differences to the indicator used in the National Drought Monitoring Framework (the Australian Rainfall Deficiency Analyser) which relies on rainfall alone.
• The CDI has three drought categories that characterise NSW according to drought intensity as well as the main drivers of a drought event (meteorological, hydrological and agronomic). DPI considers areas Drought Affected to be experiencing a drought event.
• The Drought Affected category encompasses a wide range of conditions from the very early stages of drought entry through to a drought event becoming intense. This enables the drought monitoring system to detect a drought event early. It is also possible to stay in the Drought Affected category for some period of time.

The way in which the indicators are combined to form the CDI is described in Table 1 below.

Table 1: Description of the Combined Drought Indicator framework

The NSW State Seasonal Update is provided each month by the NSW DPI Climate Branch.

Information used in this report was primarily sourced from the Australian Bureau of Meteorology, the US National Oceanic and Atmospheric Administration, the International Research Institute for Climate and Society (Columbia University), Geoscience Australia’s Digital Earth Australia Program, and NSW Department of Primary Industries.

Maps in this document contain data which is © Spatial Services – NSW Department of Finance, Services and Innovation (2021), Panorama Avenue, Bathurst 2795 and data which is © Commonwealth of Australia 2021, Australian Bureau of Meteorology, Melbourne. All rights reserved.

The seasonal outlooks presented in this report are obtained from the Australian Bureau of Meteorology and other sources (including World Meteorological Organisation Global Producing Centres). These outlooks are general statements about the likelihood (chance) of (for example) exceeding the median rainfall or minimum or maximum temperatures. Such probability outlooks should not be used as categorical or definitive forecasts, but should be regarded as tools to assist in risk management and decision making. Changes in seasonal outlooks may have occurred since this report was released.

All climate and remote sensing input data is supplied to the Enhanced Drought Information System ™ under the Australian Creative Commons Licence (CCY 4.0) and is made available by the Terrestrial Ecosystem Research Network.