NSW State Seasonal Update - July 2020

Prepared by NSW DPI

NSW overview

The drought event weakened across much of New South Wales (NSW) during July 2020. Significant rainfall along the coast, central west and central and southern Tablelands continued drought recovery for much of central and eastern NSW. Some districts in the central west of the state are now clearly out of drought. The State’s western regions did not receive significant rainfall and drought conditions continue in this part of NSW. Official climate outlooks indicate an increased likelihood of a wet spring for NSW. If the currently weak La Nina and negative IOD patterns continue to strengthen, NSW has an increased chance of above average spring rainfall, including flood events.

The weakening drought event is reflected by the NSW DPI Combined Drought Indicator (CDI). The proportion of NSW in drought has fallen to 78.5% (as of 31 July). Much of the state remains in the Drought Affected category, which in many eastern districts includes the early stages of the recovery. The individual drought indicators are now very close to the Non-Drought category in these regions, and the transition to non-drought is expected to continue over the coming month.

In contrast, most districts in western NSW remain in the Drought Affected category of the CDI. There has been little change to drought conditions or prospects of a sustained drought recovery. There are also areas in the far west that remain in the Intense Drought category. Field reports and the available remote sensing data continues to indicate that field conditions are complex across the region with significant district and farm level variability. The prolonged drought event continues in Western NSW.

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.

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.

Drought Duration

Drought duration is an important component of a drought events’ impact on farm businesses and communities. The drought duration map (Figure 2) shows the number of months since June 2017 that an area in NSW has been in one of the three CDI drought categories. The map shows that NSW continues to experience long-term drought conditions at 31 July 2020. Despite some Drought Affected areas experiencing the transition towards drought recovery, the majority of NSW has experienced drought conditions for longer than two years.

*Note: The accumulated months reported are non-consecutive.

Rainfall

The rainfall anomaly data shows the difference between total monthly rainfall and the long-term average (1961-1990; Figure 3a). Positive July anomalies were recorded throughout central and eastern NSW and were highest along the coast particularly in the South East Local Land Services region between Bega and Wollongong. Rainfall was lower than average for the majority of western, southern and northern NSW.

July rainfall totals varied across NSW (Figure 3b). The Western Local Land Services (LLS) region received falls of between 0-50mm. Central areas received totals between 10-100mm and higher falls were recorded along the eastern seaboard. Very high falls (above 300mm) were recorded for parts of the South East LLS regions.

Rainfall accumulation for 2020 has been near or above average for most of NSW, however some areas in the far west of the state continue to experience dry conditions. Large areas east of the Great Dividing Range have accumulated totals of above 600mm (Figure 3c). Higher totals of more than 1,000mm have been received on the North and Central Coast and alpine region. Falls of above 1400mm have been received in parts of the North Coast LLS region. Conditions in the far west have been dry with some areas receiving less than 50mm for the year.

Temperature

Daytime temperatures in July were 0-2°C above average across most of NSW (Figure 4a). The average daytime temperatures recorded in July (Figure 4b) were 12°C across most of NSW. The tablelands areas and southern slopes were cooler ranging between 9-12°C. Areas at higher altitudes in the tablelands and alpine areas experienced daytime temperatures between 0-9°C.

Overnight temperatures were 0-2°C below average across most of western NSW in July (Figure 4c). In contrast, overnight temperatures across most of eastern NSW were 0-2°C above average. Generally, the state experienced overnight temperatures between 0-6°C. Temperatures in most coastal regions ranged between 6-12°C. Higher altitudes in the tablelands received temperatures between -3 to 3°C, while alpine regions received overnight temperatures ranging between -6 to 3°C.

The frost days map (Figure 4e), shows the number of days that overnight temperatures did not exceed 0°C across the state in July. The areas receiving frost conditions increased from June as we move through winter.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 5) indicates that drought conditions continue to weaken in many areas of the state during the late Autumn and early-to-mid winter period. Plant greenness levels are close to normal or above normal across much of the eastern and central NSW.

The analysis also highlights regions that are still experiencing below normal levels of greenness. Plant greenness is below normal in many western areas, as well parts of the North West and South East areas of the State. 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 indicates that dam levels in much of central NSW have been improving since April and are generally above 60% of capacity. Parts of the Riverina and Murray Local Land Services (LLS) regions have also experienced improvements, though there is still a high variability in these regions. Severe deficiencies remain across large parts of the Western, Riverina, Murray and South East LLS regions.

Rainfall in the latter half of July has not been captured in this assessment of the farm dam survey.

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 west, central and southern tablelands and part of coastal NSW are showing a positive response to recent rainfall. A similar trend is indicated for accumulated pasture growth over the last 30 days in these regions.

Soil Water Index

There has been an improvement in the Soil Water Index (SWI, Figure 8) since the June Update due to rainfall over recent months. Large parts of the Central West Local Land Services (LLS) region, extending into the Riverina, Western and North West LLS are currently at average levels. The far west, south east and north east continue to be experiencing 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 Central West transitioning into the average category during July. However, parts of the far west, south east and north east continue to be experiencing 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 large areas of NSW. The majority of NSW continues to be average to below average and remains stable since the June State Seasonal Update. The majority of the Greater Sydney Local Land Services region transitioned into the above average category during July.

Drought Direction Index

The Drought Direction Index (DDI, Figure 11) tracks the trend of rainfall accumulation relative to long-term data. The DDI shows that most of the state is displaying a weak to strong drying trend due to insufficient rainfall over recent months relative to rainfall accumulation over the last five months. The exception to this is currently occurring across large areas in the South East Local Land Services (LLS) region, parts of Hunter and the North Coast which are exhibiting a weak to 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.

CDI status for the regions

Figure 12 displays the CDI status for each individual Local Land Services regions to 31 July 2020. The regional descriptions are based on data available until the end of July 2020.

Murray and Riverina regions

Rainfall in July combined with cooler winter temperatures has maintained conditions across the north of the Riverina Local Land Services (LLS) region and the alpine region in the Murray LLS region. The Combined Drought Indicator (CDI) shows most of the region is still in the Drought Affected CDI category (Figure 13), however these areas remain well positioned for recovery if adequate rainfall is received over the next three months.

On-ground reports indicate that areas further west need substantial rain to improve conditions and maintain winter crop potentials. Consistent rainfall is needed to improve soil moisture levels prior to Spring.

The seasonal NDVI anomaly data (Figure 14) has shown similar plant greenness anomalies since the June State Seasonal Update. Except for the western area, much of the region is experiencing normal to higher than normal plant greenness for the May to July 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 late winter. The Moulamein charts show how conditions plateaued during May to June and are gradually declining. This is an example of a how some areas, particularly in the west, need further rain to sustain recent 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

Autumn rainfall improved conditions in many parts of the Western Local Land Services region (LLS). However, due to a drier than average June and July, the region continues to manage long-term drought conditions. On-ground reports indicate the rainfall that has been received has been extremely variable and that the response to rainfall has been mixed.

While the drought weakened in some parts of the Western LLS region over recent months, most of the region has not had any relief. A series of effective rainfall events is still needed to initiate a substantive change in conditions and initiate any transition towards drought recovery. As of 31 July 2020, the CDI shows that most of the region is in one of the three CDI drought categories (Figure 16). Ongoing drought conditions have been experienced across Western LLS region for over 2 years (Figure 2).

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 May to July period. Many parts of the region continue to be experiencing below normal levels of greenness (brown areas on the map). Other regions are experiencing positive plant growth response.

Given the inherent nature of the environment in western NSW, it is likely that drought recovery will remain variable and take time. There has been a long-term absence of consistent rainfall across the region. A consistent rainfall pattern is needed to support a long-term sustained recovery.

The time series charts (Figure 18) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. Bourke and Ivanhoe have experienced a recent improvement compared to Wentworth; however, follow-up rainfall is needed to continue these improvements. There is an example of a false early-stage recovery at Ivanhoe in April and May 2019. This highlights the importance of follow-up rainfall for sustaining the potential of 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 July has helped improve conditions across the south and southeast of the North West Local Land Services (LLS) region. Elsewhere conditions have generally remained unchanged since the June State Seasonal Update. The area of Non-Drought in the North Coast LLS region expanded due to good follow up rainfall during the month. Large areas of the three LLS regions continue to be in the Drought Affected or Drought categories and continued rainfall is needed leading up to and throughout spring to sustain improvements longer-term.

The remote sensing satellite data shows encouraging levels of plant greenness for the May to July 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 early 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 continues to experience poor conditions, highlighting the variability in rainfall being received across the three regions. Further time is needed to gauge the effect of the rainfall that was received later in the month across various parts of the regions.

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

The Central West Local Land Services (LLS) region has experienced a substantial improvement in conditions since the June State Seasonal Update. The other three LLS regions continue to track improving conditions, where consistent rain over recent months has brought many areas out of drought. Generally, the region remains well placed for recovery to continue with the current seasonal outlook remaining favourable.

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. Drought conditions have impacted these regions for an extended period, where the soil moisture and plant growth indices struggled to surpass the lowest 10th percentile of the long-term data. The rain in recent months has improved the indicators with many areas transitioning to 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

Despite variable conditions occurring across the South East Local Land Services (LLS) region in recent months, high July rainfall totals has improved conditions across the region. Cold winter conditions are still likely to reduce plant growth activity in the short-term, however the recent improvement to soil moisture levels should provide pasture growth potential when temperatures begin to warm in spring. If favourable conditions continue for the remainder of winter and into spring, the South East LLS region will be well placed for a longer-term drought recovery.

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. 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 Bega and Cooma has cause these regions to transition out of the Intense Drought category. Further rainfall and warmer conditions will aid plant growth and aid recovery in these areas. Conditions at Goulburn have continued to remain steady over the past few months.

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 latest official national outlook was released by the Bureau of Meteorology (BoM) on 30 July 2020. The outlook for August to October indicates a wetter than average three-month period for most of the eastern two thirds of Australia. The north-west of WA is likely to be drier than average. The period between 3-16 August is likely to have average rainfall across large parts of the Australian interior, extending across SA, NSW and parts of Queensland and Victoria.

The tropical Pacific Ocean is expected to approach La Niña levels over the coming months, while warmer than average waters are likely in much of the central and eastern Indian Ocean. Both ocean basins are influencing the wetter August to October outlook.

Daytime and overnight night temperatures are likely to be warmer than average across Australia during August to October, 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. Parts of western NSW have higher probability of exceeding median rainfall during the period (Figure 28).

The BoM temperature outlook for August to October (Figure 29 & 30) indicates there is a strong probability that daytime temperatures will be warmer than median across NSW, especially east of the Great Dividing Range. There is a very strong probability that overnight temperatures will also be above median across the state due to increased cloudiness.

Global climate drivers

El Niño–Southern Oscillation (ENSO)

The Bureau of Meteorology’s (BoM) El Niño–Southern Oscillation (ENSO) Outlook was released on 4 August 2020. A La Niña WATCH status remains in place, indicating the chance of La Niña forming in 2020 is around 50%— roughly twice the average likelihood.

Surface and sub-surface waters have cooled in the tropical Pacific Ocean since April 2020. The latest weekly values have continued this trend. All surveyed international climate models anticipate further cooling is likely in the coming months with most models exceeding the La Niña threshold during spring.

Other ENSO indicators, such as the Southern Oscillation Index (SOI), trade winds, and cloudiness near the Date Line are ENSO neutral but show signs consistent with a developing La Niña. The latest trade winds have been stronger than average while the SOI has increased since the beginning of July. Equatorial cloudiness near the Date Line is below average.

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

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the period ending 2 August was +3.2. The 90-day value was −0.4. Both are within the ENSO-neutral range.

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)

The July monthly SST map shows a decrease in extent and intensity of cooler than average SSTs in the eastern tropical Pacific Ocean compared to June. In some of the equatorial Pacific, closer to the South American coast, the anomalies have strengthened. Cool anomalies persist along the equator extending from the South American coast to 150°W. Warmer than average SSTs in the western equatorial Pacific and in the Tasman Sea have generally weakened compared to June.

The July values of the three key NINO indices were: NINO3 −0.3 °C, NINO3.4 0.0 °C, and NINO4 +0.2 °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 July) shows areas of cooler than average water in the eastern equatorial Pacific between a depth of around 100 – 200m. The sub-surface temperatures in the eastern equatorial Pacific are also cooler in the top 100m. Compared to June, the strength and extent of cooler than average water has decreased.

Weak warm anomalies persist across much of the column depth west of the Date Line.

Since January, the pattern of cooler anomalies at depth has persisted, providing conditions favourable for potential La Niña development, although July has seen some weakening of these patterns.

Indian Ocean (IOD)

Much of the eastern Indian Ocean remains warmer than average, although the Indian Ocean Dipole (IOD) is currently neutral. The latest weekly value to 2 August was +0.28 °C.

One of the six international climate models surveyed by the Bureau exceeds the negative IOD threshold during August, a second joins in September, and a third reaches the threshold in October. The other three models maintain neutral values throughout the outlook period.

A negative IOD typically brings above average winter–spring rainfall to much of southern 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 currently positive and is expected to further increase to strongly positive values over the coming week before declining but remaining positive for the remainder of August.

A positive SAM at this time of year would typically see below average rainfall across far southern parts of Australia but can increase rainfall in northern New South Wales and southern Queensland.

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.nsw.gov.au.

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: The way in which the indicators are combined to form the CDI.

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