NSW State Seasonal Update - August 2020

NSW overview

Prepared by NSW DPI

NSW overview

The drought event continued to weaken across much of NSW during August. The area in non-drought has expanded and much of NSW is well positioned for longer-term recovery. The NSW DPI Combined Drought Indicator (CDI) shows that 65% of NSW is now in the Non-Drought or Recovery categories. The official climate outlook for spring indicates high probabilities of receiving above median rainfall for NSW. The development of a possible La Niña event and negative Indian Ocean Dipole (IOD)-like conditions strengthened during the month. These conditions are associated with above to well-above median rainfall during spring, including the possibility of flood events.

Satellite data and on-ground reports confirm that conditions have improved during the month, particularly in central and some eastern regions of the state. The strength of drought recovery increased in parts of the Riverina, Murray and south east of the state.

Despite these improvements, conditions across parts of western NSW remain poor. Parts of western NSW continue to manage long-term drought and further widespread rain is required to generate longer-term improvements to conditions.

Cropping regions are currently monitoring conditions. On-ground reports currently signal risk to winter crop yield in parts of the northern and western crop area and rain is needed to minimise potential losses in these areas. In contrast, other cropping areas have maintained high yield potential, especially in central regions. Based on the latest seasonal outlook, an emerging risk of wet harvest conditions is a possibility for some regions.

Spring pasture growth potential remains high across central and most of eastern NSW. Temperatures will have a large bearing on growth rates in spring. Growth rates are typically slower to respond at higher altitudes where conditions remain colder for longer.

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

The rainfall anomaly data shows the difference between total monthly rainfall and the long-term average (1961-1990; Figure 2a). Higher than average August anomalies were recorded throughout southern and western NSW and were highest in the South East Local Land Services region. Rainfall was lower than average for the majority of the central to north-eastern regions of NSW.

August rainfall totals varied across NSW (Figure 2b). The Western Local Land Services (LLS) region received falls of between 10-100mm. Central areas received totals between 25-200mm, and higher totals were recorded along the eastern seaboard. Very high falls (above 200mm) were recorded for parts of the South East LLS region and alpine areas.

Rainfall accumulation for 2020 has been near or above average for most of NSW, however some areas in the far west and north-east of the state continue to experience 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 1400mm in the North Coast and South Coast LLS regions, Blue Mountains and alpine region. Conditions in the far west have been varied, with parts of the region receiving less than 100mm for the year.

Temperature

Daytime temperatures in July were generally average (+/- 1°C) across most of NSW (Figure 3a). The average daytime temperatures recorded in August (Figure 3b) ranged between 12 and 24°C across most of NSW. The tablelands areas and southern slopes were cooler ranging between 9-15°C. Areas at higher altitudes in the tablelands and alpine areas experienced daytime temperatures between 0-9°C.

Overnight temperatures were generally average (+/- 1°C) across NSW in August (Figure 3c). Temperatures anomalies were slightly above average (1-2°C) in the north west and slightly below average in parts of central NSW (-1 to -2°C). Most of NSW experienced overnight temperatures between 0-9°C during August (Figure 3d). Temperatures in most coastal regions ranged between 6-12°C. Higher altitudes in the tablelands recorded temperatures between -3 to 3°C, while alpine regions received overnight temperatures ranging between -6 to 3°C.

The frost days map (Figure 4), shows the number of days that overnight temperatures were less than 0°C across the state in August. A cold front moving across the state caused an increase in frost days during the last week of August and potentially caused yield damage to susceptible crops in parts of the states cropping regions.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 5) indicates that plant greenness levels are close to normal or above normal across much of the eastern and central NSW for the June to August period. Parts of the South East are slowly responding to rainfall over the last 6 weeks. 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.

Severe plant greenness deficiencies are still 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, Riverina, North West and Northern Tablelands Local Land Services (LLS) regions, where levels are below 20% of capacity. Elsewhere dam levels are generally above 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 much of the central and eastern NSW is showing a positive response to recent rainfall. A similar trend is indicated for accumulated pasture growth over the last 30 days in these regions, though accumulated pasture growth in western NSW shows a weaker response.

Individual drought indicators

Soil Water Index

There has been an improvement in the Soil Water Index (SWI, Figure 8) since the July Update 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 transitioning into the average category during August. However, parts of the far west, south east and north east continue to be experiencing below average to extremely low plant growth values. This is reflected 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 neutral to weakly drying/wetting trend. Strong drying trends are currently occurring across parts of central, southern and northern NSW. Parts of Hunter, Greater Sydney and South East LLS regions are exhibiting strong wetting trend. This is a result of recent rainfall in these areas.

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 31 August 2020. The following regional descriptions are based on data available until the end of August 2020.

Murray and Riverina regions

Rainfall and cooler temperatures during August have maintained conditions across most of the Riverina and Murray Local Land Services (LLS) regions. The Combined Drought Indicator (CDI) shows that large areas transitioned to the Recovery or Non-Drought CDI category during August (Figure 13). There are areas still in the Drought Affected category and will need rain to maximise spring potential prior to conditions turning hot in summer.

On-ground reports indicate that areas further west need rain to maintain conditions and winter crop potentials. Some crops have excellent potential but there are increasing crop demands for soil water as spring temperatures increase.

The seasonal NDVI anomaly data (Figure 14) has shown similar plant greenness anomalies since the August State Seasonal Update. Except for some western areas, much of the region is experiencing normal to higher than normal plant greenness for the June to August 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 rainfall continues during early spring. The Moulamein charts show how conditions plateaued during May to June, though recent rainfall has helped to improve conditions. Further rain is needed to sustain these improvements.

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 August. Many areas recorded their highest monthly totals in several months, however the rainfall distribution continues to be highly variable. Some areas are now well placed for early stage recovery. The Combined Drought Indicator (CDI) shows that the area of Recovery and Non-Drought expanded in the region during August (Figure 16). This is due to rainfall accumulation over the past 12 months.

However, NSW DPI continues to advise that various parts of the Western LLS is still enduring long-term drought conditions. On-ground reports and remote sensing data (Figure 17) indicate slow responses to rainfall in some districts and this continues to be a major challenge in the western region. The slow response could be caused by several factors including irregular rainfall consistency, extended duration between rain events and the complex interaction between rainfall intensity, soil type and runoff dynamics. On-ground reports also confirm high variability between farms and regions. Ultimately large parts of the region have experienced an extended absence of consistent rainfall needed to support a long-term recovery, while other districts are experiencing excellent conditions at the start of Spring. Given the inherent nature of the environment in western NSW, it is likely that drought recovery will 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 June to August period. Many parts of the region continue to be experiencing below normal levels of greenness (brown areas on the map). Other regions are experiencing excellent plant growth conditions for the period.

The time series charts (Figure 18) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. All three locations have responded to recent rainfall. However, drought conditions remain and follow up rainfall is needed to aid any potential longer-term 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

Rainfall during August has helped improve conditions across parts of the North West, Northern Tablelands and North Coast Local Land Services (LLS) regions (Figure 19). Despite this, on-ground reports indicate that some winter crops are showing signs of yield decline and need further rain. Some crops have excellent potential but there are increasing crop demands for soil water as spring temperatures increase. Rainfall accumulation during the winter was below average across much of the crop growing districts, while most of the north coast has accumulated below average rainfall over the last 6 months.

The remote sensing satellite data shows encouraging levels of plant greenness for the June to August period. The seasonal NDVI anomaly data (Figure 20) indicates positive anomalies across much of the region for the period. The data indicates that rainfall received earlier in the year was effective for improving pasture and on-ground conditions during autumn and winter.

The time series charts (Figure 21) show the individual response of the drought indices for Moree, Walgett and Tenterfield. There has been a varied response to the rainfall in recent months. The drought indices have improved substantially at Walgett and Moree over recent months, however as in the case of Lismore, follow-up rainfall is crucial for sustaining improvement to conditions. Tenterfield has seen a slight improvement to the rainfall index due to recent rainfall, however the location continues to experience poor conditions and further rainfall is needed to. The difference between the site highlights the variability in rainfall being received across the regions.

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 winter. The Central West and Greater Sydney LLS regions received timely and effective rainfall throughout winter and have transitioned out of the various Combined Drought Indicator drought categories (Figure 22) and maintain a good prognosis for spring. Elsewhere the transition towards drought recovery remains strong with good conditions expected to unfold during spring.

The seasonal NDVI anomaly data (Figure 23) generally indicates a positive response to rainfall during autumn and early-to-mid winter. The remote sensing satellite data currently shows above expected levels of plant greenness across large areas of these LLS. 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

The South East Local Land Services (LLS) region has experienced a rapid change in conditions due to favourable July and August rainfall. The rain improved the status of the Combined Drought Indicator (CDI) and continued to strengthen the transition towards recovery in the northern districts of the LLS region where there is now excellent spring potential (Figure 25). Further south, the rain has brought relief to most areas that have been exposed to longer durations of Intense Drought. Despite this, a change to on-ground conditions is expected to take time and warmer spring temperatures will be needed to initiate rapid pasture growth in many districts. Most areas in the south are still likely to need follow-up rainfall during spring to maintain the sustained transition towards recovery in the lead up to summer.

The seasonal NDVI anomaly data (Figure 26) shows a higher than expected level of plant greenness in much of the north. Rainfall totals have been higher and more effective in these areas over recent months. Plant greenness levels remain below expected levels in the south and the areas impacted by bushfires continue to stand out.

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 caused improvements to on-ground conditions. Further rainfall and warmer conditions will aid plant growth and aid recovery.

Seasonal climate outlook

Official national outlook

The latest official national outlook was released by the Bureau of Meteorology (BoM) on 3 September 2020. The outlook for September to November indicates a wetter than average three-month period for most of the eastern two thirds of Australia. Western Tasmania and western parts of Western Australia is likely to be drier than average.

Daytime and overnight night temperatures are likely to be warmer than average across most of Australia during September to November, though chances of warmer or cooler than average days and nights are roughly equal across much of south-west WA.

NSW outlook

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

The BoM temperature outlook for September to November (Figure 29 & 30) indicates there is an increased likelihood that daytime temperatures will be warmer than median across NSW. There is also a very strong probability that overnight temperatures will also be above median across the state.

Global climate drivers

El Niño–Southern Oscillation (ENSO)

The Bureau of Meteorology’s (BoM) El Niño-Southern Oscillation (ENSO) Outlook was released on 30 August 2020 and is currently at La Niña ALERT. Climate models suggest that a La Nina is likely in spring. This is due to recent cooling of sea surface temperatures in the tropical Pacific Ocean and associated changes in tropical atmospheric patterns. Continued cooling of ocean temperatures is predicted by models. Five of the eight models reach or exceed La Niña thresholds during October, with six models indicating that if La Niña forms it is likely to persist into December.

Trade winds are currently stronger than average. Generally during a La Niña, there is a sustained strengthening of the trade winds. Equatorial cloudiness near the Date Line has been below average during the past fortnight and generally been below average since mid-March. Equatorial cloudiness near the Date Line typically decreases during La Niña.

La Niña typically increases the chance of above average rainfall across much of Australia during spring.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI, Figure 31) for the 30 days ending 30 August was +9.1. The 90-day value remains within the ENSO-neutral range at +2.3.

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)

Weekly sea surface temperature (SST) anomalies for August (Figure 32) were cooler than average across the central and eastern equatorial Pacific Ocean, but still within the neutral ENSO range. Anomalously warm sea surface temperatures are present in the western equatorial Pacific Ocean and in the Tasman Sea.

The latest weekly values (to 30 August) for the three key NINO indices were: NINO3 −0.5 °C, NINO3.4 -0.5 °C, and NINO4 0°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 (Figure 33) to 27 August shows cooler than average water extending across the top 150 m of the sub-surface of most of the equatorial Pacific. The strength and extent of cooler than average water has increased since July. Weak warm anomalies persist west of the Date Line. The pattern of cooler anomalies has persisted for several months and supports the potential for La Niña development.

Indian Ocean (IOD)

The Indian Ocean Dipole is currently negative (-0.49°C as of 30 August 2020). There are large areas of the Indian Ocean which are warmer than average. Weak, cool anomalies exist in the west of the basin.

Three of the six surveyed climate models indicate that the IOD will remain at weak negative levels during September, and four of the six models remain weakly negative for October and 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 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.

The Southern Annual Mode (SAM) is negative (Figure 34). It is expected to become neutral during September.

At this time of year, a negative SAM is typically associated with above-average rainfall across far southern parts of the Australia and below average rainfall further north.

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 9.