NSW State Seasonal Update - August 2021

Prepared by NSW DPI

NSW overview

Average to above average winter rainfall has supported a strong seasonal production outlook for much of NSW. August rainfall was below average across most of the state, but this does not heavily influence the strong production outlook for NSW. The NSW DPI Combined Drought Indicator (CDI) shows 93% of NSW in the Recovery or Non-Drought categories at the end of August. The seasonal rainfall outlook indicates high chances of above median Spring rainfall across NSW.

Despite the strong overall outlook there are production risks from seasonal conditions in some areas of NSW. 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 an extended dry period since substantial rain in March. The dry August will have started to alleviate waterlogging and localised flooding concerns that emerged in June-July, but due to high levels of soil moisture many areas remain vulnerable, particularly the slopes, central and tableland districts.

The 2021 winter crop potential remains high, however conditions are variable across the grain belt.  There are ongoing risks of waterlogging in cropping fields in the central and tablelands districts. In contrast, parts of the south-west grains region experienced dry conditions in August and these regions need further rain to maintain yields.

Winter rainfall accumulation has improved the state’s reservoir and irrigation scheme levels over the last six months. Water availability has increased and is expected to support a strong irrigated crop forecast for the 2021-22 season.

High winter rainfall also provides high pasture growth potential and livestock productivity across most of NSW. Soil moisture levels and increasing Spring temperatures should begin to accelerate pasture growth in the next several weeks, especially in eastern NSW.

The latest Bureau of Meteorology (BoM) Seasonal Outlook indicates high chances of above median Spring rainfall across NSW. A negative Indian Ocean Dipole (IOD) event continues and is forecast to peak in mid-Spring. 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 NSW received average to below average rainfall in August. The North Coast and eastern areas of the Riverina and Murray LLS regions recorded the largest deficits of 25-100mm during the month. The New England, parts of the Central Tablelands and far southern areas of the South Coast LLS regions received 25-50mm above the August average.

Rainfall totals were variable across NSW during August (Figure 2b). The higher rainfall totals were received in parts of Northern, Central and Southern Tablelands, as well as parts of the South and Central Coast. Alpine areas received 100-200mm in the month. The far-north west received less than 10mm.

Rainfall accumulation during the 2021 calendar year has been near or above average across eastern NSW. Most of coastal NSW and the Tablelands areas have received more than 600mm in the year (Figure 2c). Parts of the North Coast 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 above average maximum temperature anomalies of 1-3°C during August (Figure 3a). The average August maximum temperatures were generally above 15°C across NSW, with cooler temperatures in the Tableland and Alpine regions (Figure 3b). Much of northern NSW received maximum temperatures ranging between 21-24°C.

Minimum temperatures were near average across most of NSW in August, however northern parts of the Western LLS region experienced lower than average minimum temperatures. (Figure 3c). Mean minimum temperatures ranged between 3-6°C across most of the state (Figure 3d). Tablelands and Alpine regions at higher altitudes experienced cooler temperatures between -3 to 3°C.

Frost incidences were high in the slopes, tablelands and Alpine zone during the last month of the 2021 Winter (Figure 3e).

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 June to August 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%.

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 at the end of August.

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 August. Parts of south-western, western and the North Coast regions were in the below average 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 that the south-west of NSW currently has a wetting trend, largely due to rainfall in June and July. Coastal areas are showing a drying trend reflecting the extent of rain deficits that occurred during winter.

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 31 August 2021. The following regional descriptions are based on data available until the end of August 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 remain in the Drought Affected category at the end of August. 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 June to August 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. The charts show the indicators improved during early winter but have plateaued or declined in August. Follow-up rainfall remains a focus to build these indicators during Spring, especially at Moulamein, Hay and other western locations. 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 the majority of the Western LLS region is in the Non-Drought category, however there was an increase in the Drought Affected category during August. The south-western area of the LLS region continues to remain in the Drought Affected category and drought recovery has remained variable, weak or delayed in these districts. 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 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 June to August period. Large areas of the far west and south-west have low plant greenness levels.

The time series charts (Figure 16) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. Conditions generally improved or remained stable in early winter but declined at Bourke and Wentworth in August. Ivanhoe received higher winter rainfall causing the indicators to increase throughout winter. The DPI continues to monitor conditions closely across the Western LLS. 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 rainfall has supported drought recovery across the North West and Northern Tablelands Local Land Service regions. The North Coast LLS region experienced a dry winter in comparison, 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. The risk of waterlogging remains high in some areas, and the NSW DPI is closely monitoring conditions on 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 June to August period.

The time series charts (Figure 19) show the individual response of the drought indices for Moree, Walgett, Tenterfield and Lismore. The indicators continued to increase at Tenterfield and Moree during winter but declined at Walgett and Lismore in August. 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 August (Figure 20). Most of the regions remain in a strong position for 2021 Spring production, with high soil water levels in many areas. The risk of waterlogging continues, especially in parts of the Central Tablelands and Central West. Parts of the Hunter LLS have experienced a comparatively drier winter. 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 June to August 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 August 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. Most of the South East LLS region remains well positioned for a productive 2021 Spring period. The CDI shows that an area around Nowra is currently in the Drought Affected category. This highlights the importance of consistent follow-up rain after relatively dry conditions in July.

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 August 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 charts show improvements in the indices at Bega and Cooma during early winter but a decline in August. This reflects the drier conditions in late winter. The indices at Goulburn show a dry period in April and May, however winter rainfall has maintained the indicators at higher levels at the end of August.

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 2 September 2021. Spring rainfall is likely to be above median for the eastern two-thirds of Australia. Below median rainfall is likely for parts of western WA and south-west Tasmania.

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 southern WA.

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 during Spring (Figure 26). The daytime temperature outlook indicates near equal to 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 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 31 August 2021. The ENSO Outlook status remains neutral. Sea surface and sub-surface temperatures have cooled in the central tropical Pacific over recent months. Most models surveyed by the BoM indicate that while sea surface temperatures are cool, they are unlikely to fall below La Niña thresholds in Spring.

While the current forecast of a potential La Niña event is weak, the cooling of the central tropical Pacific is likely contributing to the increased chance of above median rainfall across NSW during Spring.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 29 August 2021 was +3.5. The 90-day SOI value was +7.9. The 30-day value has been remained within neutral values over 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. Small areas of slightly cooler than average SSTs have increased in the central to eastern equatorial Pacific in the last fortnight, 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 29 August were: NINO3 -0.1°C, NINO3.4 -0.3°C, NINO4 0°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

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to 26 August) shows a pattern consistent with a neutral ENSO state. Cool sub-surface anomalies have intensified in the central to eastern equatorial Pacific during the month.

Indian Ocean (IOD)

The negative Indian Ocean Dipole (IOD) event is likely to persist during spring, although current values have weakened and have fallen outside threshold levels during the past fortnight. The latest weekly value of the Indian Ocean Dipole (IOD) index to 29 August 2021 was −0.35 °C. The IOD index has generally been below the negative IOD threshold (−0.4 °C) since mid-May.

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 over the past week and is forecast to remain positive for the next fortnight. A positive SAM typically has a drying influence on south-west and south-east Australia during winter, but increases the chance of above average rainfall for much of New South Wales during spring.

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.