NSW State Seasonal Update - September 2020

NSW overview

Prepared by NSW DPI

NSW overview

Conditions continued to improve across much of NSW during September 2020. Many regions are currently experiencing very high levels of spring productivity. The area of non-drought continues to expand as recovery builds across much of the state. The NSW DPI Combined Drought Indicator (CDI) now shows that 76% of NSW is in the Non-Drought or Recovery categories. Full recovery from drought can take 6-18 months of favourable seasonal conditions. The official climate outlook indicates high probabilities of above median rainfall for most of NSW over the next three months. A La Niña event has established and will likely persist into January 2021. La Niña is associated with above to well-above median rainfall during spring, including the possibility of flooding.

Spring pasture growth remains high across central and most of eastern NSW, while September rain has improved pasture growth in parts of western NSW. Warm spring temperatures will increase growth rates at higher altitudes, especially where winter and early spring rainfall has increased soil moisture reserves.

September rainfall maintained excellent winter crop yield potential in the central and southern crop zones. The summer crop planting window is now open, and rain would assist sowing conditions. Irrigated crop potential remains poor in northern irrigation valleys. Rainfall has not been sufficient to increase reservoir storage levels significantly, and the availability of irrigation water remains low.

Conditions across parts of western NSW improved after follow-up rain was received in September, however variability still exists and any recovery is poor in some regions. The continuation of widespread follow-up rain is still a focus for much of the Western Region, especially now that temperatures have increased.

Rainfall in north-eastern NSW has been below average over the past six months. Despite the improvements experienced since early autumn, follow-up rainfall is needed to maintain confidence of longer-term recovery. The far south-east of NSW would also benefit from follow-up rain to strengthen recent improvements in conditions.

On-ground reports suggest that the frost events in early and late September have caused damage to horticultural and winter crops in some areas, while hail damage to winter crops in parts of the Central West and Riverina were also reported during the month.

The CDI and its individual rainfall, soil moisture and crop/pasture growth metrics are leading biophysical indices of drought. While the CDI currently points to a strengthening recovery and transition out of biophysical drought for parts of eastern NSW, production and economic responses lag behind 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.

Drought Support

Producers and members of rural communities are encouraged to maintain contact with their local professionals who can facilitate access to appropriate support. If you or someone you know needs support, please visit DroughtHub. Alternatively, you can contact the DPI Rural Resilience Team, Rural Financial Counsellors, or your Local Land Services representatives.

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

Rainfall accumulation for 2020 has been approaching average or higher for most of NSW, however some areas continue to experience average to below average rainfall. Large areas across eastern NSW have accumulated totals of above 600mm (Figure 2c). Higher totals of more than 1,000mm have been received along parts of the eastern seaboard, with falls above 1,400mm in the North Coast and South Coast LLS regions, Blue Mountains and alpine region. Conditions in the far west have varied, however most of the region has now received 100mm or more following rain in September.

Temperature

Maximum temperatures in September were generally 2-3°C higher than average across most of western NSW and were 1-2°C higher than average in eastern areas (Figure 3a). The average maximum temperatures recorded in September (Figure 3b) were warmest across northern NSW (above 24°C). Elsewhere temperatures ranged between 12-24°C and the alpine regions experienced maximum average temperatures between 6-15°C.

Minimum temperature anomalies for September were generally 1-2°C warmer than average across most of NSW (Figure 3c), and 2-4°C warmer than average in parts of western and northern NSW. Most of north west and coastal NSW experienced average minimum temperatures between 9-15°C during the month (Figure 3d). Elsewhere minimum temperatures ranged between 6-9°C but were lower in the tablelands and in some southern regions (0-6°C).

The frost days map (Figure 4), 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, however the timing of these frosts may have led to damage to susceptible winter and horticultural crops.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 5) indicates that plant greenness levels are close to, or above normal across much of the eastern and central NSW for the July to September period. Parts of the South East continue to slowly respond to rainfall received in late winter. Plant greenness levels remain variable in the Western LLS region. Below normal greenness levels continue across parts of the far western areas and in some eastern districts of the region.

Very low plant greenness remains evident in much of the bushfire affected areas of the Central Tablelands, South East and Alpine areas of the state.

Several technical factors need to be considered when considering the analysis:

It is based on the USGS Landsat satellite, quality-controlled and provided by Geoscience Australia's Digital Earth Australia program. This collects data at a 30m spatial resolution every two weeks.
Clouds and smoke can obstruct observations which can cause gaps in the NDVI data or banding in the available imagery at various times.

NSW Farm Dam Survey

The latest data from the NSW Farm Dam Survey (Figure 6) indicates that dam levels in most central regions of the state are above 40% of capacity. Severe dam deficiencies remain evident across large areas in the Western, Murray, Riverina, North West, North Coast and parts of the Northern Tablelands Local Land Services (LLS) regions, where levels are below 20% of capacity.

Short-term Soil Water and Plant Growth

The short-term response of soil water and accumulated pasture growth is shown in Figure 7a and Figure 7b. The average soil water recharge over the past 30 days indicates that that the Central Tablelands, parts of the South East and eastern areas of the Riverina and Murray Local Land Service (LLS) regions show a strong response to recent rainfall. Despite rain during the month, the Western LLS region shows a variable and lower soil water accumulation response. A similar trend is indicated for accumulated pasture growth over the last 30 days.

Individual drought indicators

Soil Water Index

There has been an improvement in the Soil Water Index (SWI, Figure 8) since mid-winter due to rainfall over recent months. The majority of NSW is currently at average levels. Parts of western, northern and southern NSW continue to be experiencing below average to extremely low soil water values.

Plant Growth Index

The Plant Growth Index (PGI, Figure 9) response generally mirrors the SWI with large areas of the NSW in the average category at the end of September. However, parts of the far west, south east and north east continue to be experiencing below average to extremely low plant growth values. Similar trends can be observed in the satellite data presented in the seasonal NDVI anomaly maps (Figure 5).

Rainfall Index

Rainfall accumulation during 2020 has improved the Rainfall Index (RI, Figure 10) across NSW. The majority of NSW is currently in the average category, with parts of the Central West, Greater Sydney, South East and North Coast LLS regions in the above average category. Parts of western, southern and northern NSW continue to be in the below average to extremely low category.

Drought Direction Index

The Drought Direction Index (DDI, Figure 11) tracks the 150-day trend of daily rainfall totals. The DDI shows that most of the state is displaying a weak to strong wetting trend. In contrast parts of the Northern Tablelands, the North Coast and the Central Coast show a weak to strong drying trend over the last 150 days.

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

Monthly regional breakdown

CDI status for the regions

Figure 12 displays the CDI status for each individual Local Land Services regions to 30 September 2020. The following regional descriptions are based on data available until the end of September 2020.

Murray and Riverina regions

September rainfall maintained conditions across most of the Riverina and Murray Local Land Services (LLS) regions. Near ideal spring conditions are currently occurring across most of the region. The Combined Drought Indicator (CDI) shows that large areas transitioned to the Recovery or Non-Drought CDI category during the month (Figure 13). Some areas remain in the Drought Affected category and rain is needed to maintain crop yields and maximise spring pasture growth prior to conditions turning hot in summer. There are increasing crop demands for soil water now that spring temperatures have increased.

The seasonal NDVI anomaly data (Figure 14) has shown similar plant greenness anomalies since the August State Seasonal Update. Much of the region is experiencing normal to higher than normal plant greenness for the July to September period. The impact of the recent bush fires is still evident south of Tumut.

The time series charts (Figure 15) show the individual response of the drought indices for Hay, Finley, Temora and Moulamein. The Hay, Finley and Temora charts show that conditions continue to transition towards drought recovery and are in a good position if follow-up rain continues. The Moulamein charts show that conditions plateaued during May to June and lag in drought recovery. Consistent follow-up rain is still needed at Moulamein to recover from drought.

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.

Western region

Much of the Western Local Land Services (LLS) region received near or above average rainfall during September. Rainfall over the past two months improved conditions across large areas of the region. Further follow-up rain remains a key focus for much of the region, especially now that temperatures have increased. The Combined Drought Indicator (CDI) shows that the area of Recovery and Non-Drought expanded during September (Figure 16), primarily due to a more consistent rainfall pattern over the past two months.

The NSW DPI advises that parts of the Western LLS still endure long-term drought conditions, as confirmed from on-ground reports and remote sensing data (Figure 17). Localised rainfall variability and mixed responses to the rainfall continue to be a challenge in the Western region. Given the inherent nature of the environment in Western NSW, drought recovery will likely remain variable and take time.

The seasonal NDVI anomaly data (Figure 17) shows the high degree of variability in plant greenness levels across the region compared to the long-term expectations for the July to September period. Parts of the region continue to be experiencing below normal levels of greenness (brown areas on the map). Other regions are experiencing above normal levels of greenness for the period and have generally improved since the last update at the end of August.

The time series charts (Figure 18) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. All three locations show variable rainfall patterns and responses in the soil water and plant growth indices. All locations continue to rely on follow-up rain to maintain or enter drought recovery. 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

September rainfall has improved conditions across parts of the North West, Northern Tablelands and North Coast Local Land Services (LLS) regions. The area in the Recovery or Non-Drought Combined Drought Indicator (CDI) expanded during the month, particularly in the south and south and south-east areas of the region (Figure 19). Conditions were generally drier in the northern areas of the region and the area in Drought or Drought-Affected categories remains unchanged.

Rainfall accumulation in winter and during September was below average across parts of the northern crop growing districts causing a wide range of yield potentials. Much of north eastern NSW has accumulated below average rainfall over the last 6 months. Further rainfall is needed to continue drought recovery, especially now that temperatures have increased.

The seasonal NDVI anomaly data (Figure 20) indicates positive anomalies across much of the region for the period. The data indicates that improvements gained from rainfall received earlier in the year has been maintained in most areas at the start of Spring.

The time series charts (Figure 21) show the individual response of the drought indices for Moree, Walgett and Tenterfield. There has been variable rainfall patterns and responses in recent months. The drought indices have improved at Walgett and Moree and the continuation of rain would maintain the recovery from drought. Lismore highlights the importance of adequate follow-up rain. A relatively dry six months means that follow-up rainfall is now crucial for sustaining any improvements gained in autumn. Tenterfield has experienced slight improvements to the rainfall index over the last six months and the location continues to lag in drought recovery.

Central Tablelands, Central West, Hunter and Greater Sydney regions

The Central West, Central Tablelands, Hunter and Greater Sydney Local Land Services (LLS) region continued the strong transition towards drought recovery during September. Winter rainfall has aided recovery and the entire Central West and Greater Sydney LLS regions continue to be in the Recovery or Non-Drought Combined Drought Indicator categories (Figure 22). Recovery has also strengthened in the Central Tablelands and Hunter LLS regions.

The seasonal NDVI anomaly data (Figure 23) continues to show above average levels of plant greenness across large areas of these LLS regions. The bushfire impact remains evident in parts of the tablelands.

The time series charts (Figure 24) show the individual response of the drought indices for Cowra, Condobolin and Singleton. Rainfall in recent months has improved the indicators with many areas transitioning to a non-drought status or towards the late stages of drought recovery.

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

Conditions continued to improve during September in the South East Local Land Services region. In the north, the Combined Drought Indicator (CDI) shows an expansion of the Recovering and Non-Drought categories when compared to August (Figure 25). Further south, rain in late winter continues to provide relief from the Intense Drought conditions experienced earlier in the year.

The seasonal NDVI anomaly data (Figure 26) shows a higher than average level of plant greenness across much of the region. Plant greenness levels remain below expected levels in parts of the south including the Monaro high plain and a small area around Bega. The areas impacted by bushfires continue to have well below average plant greenness.

The time series charts (Figure 27) show the individual response of the drought indices at Bega, Goulburn and Cooma. The recent spike in the rainfall index at these locations has improved conditions, but the plant growth index remains low is some parts of the South East due to low temperatures. Areas like the Monaro and Bega highlights the importance and need for follow-up rainfall. Further rainfall and warming spring temperatures will aid plant growth and recovery.

Seasonal climate outlook

Official national outlook

The latest official national outlook was released by the Bureau of Meteorology (BoM) on 1 October 2020. The outlook indicates that October to December is likely to be wetter than average for much of mainland Australia and north-east Tasmania. There are roughly equal chances of higher or lower than median rainfall across north-west Western Australia, while south-west Tasmania is likely to experience lower than median rainfall.

Daytime temperatures are very likely to be warmer than average along the far northern and the far south-east of Australia for the remainder of 2020. Warmer than average conditions are also likely for parts of northern Australia, while cooler than average days are likely in southern Western Australia. Overnight temperatures are very likely to be warmer than average for most of Australia, though the likelihood is reduced over the south-west.

NSW outlook

NSW currently has a moderate to high chance of exceeding median rainfall in the October to December period (Figure 28).

The BoM temperature outlook for October to December (Figure 29 & 30) indicates roughly equal chances that daytime temperatures will be warmer or cooler than median across most of NSW. The south east, north coast and parts of western NSW currently have higher chances of daytime temperatures being warmer than median. Overnight temperatures are very likely to be above median across the state for the next three months.

Global climate drivers

El Niño–Southern Oscillation (ENSO)

The Bureau of Meteorology’s (BoM) El Niño-Southern Oscillation (ENSO) Outlook was released on 29 September 2020. It announced that a La Niña event has established. A La Niña event typically increases the likelihood of above average rainfall across much of Australia during spring, and across much of eastern Australia during summer.

All surveyed international climate models indicate this La Niña will persist until at least January 2021, Currently, the models do not expect that this event will be as strong as the La Niña of 2010–12, which was one of the four strongest La Niña events on record.

Trade winds continue to remain stronger than average. Generally, a sustained strengthening of these trade winds occurs during the development and throughout a La Niña event. Equatorial cloudiness near the Date Line has been below average during the past fortnight and has generally been below average since mid-March. Equatorial cloudiness near the Date Line typically decreases during La Niña.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 27 September was +10.4. The 90-day SOI value is also above La Niña thresholds at +8.1.

Sustained positive values of the SOI greater than +7 are typical of a La Niña event.

Sea surface temperatures (SST)

Monthly sea surface temperatures (SST) were cooler than average in the central and eastern Pacific during September. (Figure 32). Warm anomalies were present in the western Pacific, extending into the Maritime Continent and into waters off much of northern and eastern Australia.

The latest values of the three NINO indices in the tropical Pacific for the week ending 27 September were: NINO3 −0.9 °C, NINO3.4 −0.8 °C, NINO4 −0.3 °C.

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 24 September) shows the top 200m of the equatorial Pacific east of the Date Line is cooler than average (Figure 33). The strengthening of the cooler anomalies has persisted for several months and has supported the development of the La Niña event.

Indian Ocean (IOD)

The Indian Ocean Dipole (IOD) is currently negative. The latest weekly value to 27 September was −0.45°C. Large parts of the central and eastern Indian Ocean are warmer than average, with surface temperatures close to average in much of the west of the basin.

Five of the six surveyed models indicate the IOD will remain negative for October. Three models continue negative IOD values into November. The IOD index needs to remain at or cooler than −0.4 °C for eight weeks for it to be classed as an official negative IOD event.

A negative IOD typically brings above average spring rainfall to most of the eastern two thirds of Australia and to south-east Western Australia.

Southern Ocean (Southern Annular Mode – SAM)

The Southern Annual Mode (SAM) is currently positive (Figure 34). It is expected to be neutral or weakly positive for the first three weeks of October (Figure 34). A positive SAM during spring is typically associated with wetter and cooler than average conditions in parts of eastern Australia. La Niña tends to favour positive SAM during spring and summer. This typically enhances the wet signal in eastern Australia.

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.

Combined Drought Indicator (CDI) explained

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

CDI Phase	Technical definition	Description - typical field conditions
Intense Drought	All three indicators (rainfall, soil water, plant growth) are below the 5^thpercentile	Ground cover is very low, soil moisture stores are exhausted and rainfall has been minimal over the past 6-12 months.
Drought	At least one indicator is below the 5^th percentile	Conditions may be very dry, or agronomic production is tight (low soil moisture or plant growth). It is possible to be in Drought when there has been some modest growth, or a few falls of rain.
Drought Affected (intensifying)	At least one indicator is below the 30^th percentile and the rainfall trend is negative over the past 90 days.	Conditions are deteriorating; production is beginning to get tighter. Ground cover may be modest, but growth is moderate to low for the time of year. When indicators are close to the Drought threshold drought conditions are severe.
Drought Affected (weakening)	At least one indicator is below the 30^th percentile and the rainfall trend is positive over the past 90 days.	Production conditions are getting tighter, but there have been some falls of rain over the past month. It is rare to enter the Recovering phase from the Non-Drought category; Usually there is a quick (1-2 week) transition into Drought Affected or Drought. When indicators are close to the Drought threshold drought conditions are severe.
Recovering	All indicators are below the 50^th percentile but above the 30^th percentile	Production is occurring but would be considered ‘below average’. Full production recovery may not have occurred if this area has experienced drought conditions over the past six months.
Non-drought	At least one indicator is above the 50^th percentile.	Production is not limited by climatic conditions.

Acknowledgments

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 (2020), Panorama Avenue, Bathurst 2795 and data which is © Commonwealth of Australia 2020, 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.

© State of New South Wales through the Department of Regional NSW, 2020. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute the NSW Department of Primary Industries as the owner.

Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (September 2020). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of the Department of Primary Industries or the user’s independent adviser.

Published by the NSW Department of Primary Industries. ISSN 2202-1795 (Online). Volume 8 Issue 10.