NSW State Seasonal Update - December 2020

NSW overview

Prepared by NSW DPI

NSW overview

Recovery from the 2017-2020 drought event continued across most of NSW during December 2020. The NSW DPI Combined Drought Indicator (CDI) shows 97% of NSW is in the Recovery or Non-Drought categories. December rainfall continued to support recovery in many regions, especially in parts of north-eastern NSW where drought persisted late into 2020. The official climate outlook indicates moderate to high probabilities of above median rainfall across NSW for the next three months.

The large 2020 NSW winter crop harvest was mostly completed in December. Rainfall during the month caused harvest delays, however, the rain has also begun to replenish soil moisture levels for the upcoming 2021 winter crop. This rain will also support the summer crop that is currently mid-way through the growing season. There were reports of increased streamflow in parts of the northern irrigation area during the month, however, reservoir storages generally remain low.

Pasture productivity in December remained favourable and continued drought recovery across most areas. Rainfall during the month increased this confidence and provided further opportunities for fodder conservation in some areas.

Despite the excellent turnaround in conditions across most of NSW during 2020, the strength of drought recovery remains low in some areas, such as Western NSW. For some farms in this region, it is questionable whether current seasonal conditions should be described as ‘drought recovery’. Rainfall patterns remain variable and the isolated nature of storm rainfall continues to persist. Some areas still require consistent rainfall patterns to build confidence of longer-term drought recovery.

The La Niña event continued to progress in the Pacific Ocean and was likely a dominant influence on the high rainfall totals received across north-eastern areas of NSW in December. La Niña typically increases the chance of higher than median rainfall across NSW, however high rainfall variability or irregularity can still be common due to the influence of localised short-term synoptic weather patterns.

Recent indications signal that the La Niña event has peaked, however it remains the dominant influence in the official Bureau of Meteorology (BoM) 3-month Seasonal Outlook released on 7 January 2021. The outlook indicates moderate to high probabilities of above median rainfall across NSW in the February to April period. The associated increased risk of flooding reported in last month’s update continues.

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 large areas of NSW, production and economic responses lag behind the CDI. Full drought recovery can take 6-18 months depending on a number of influences including rainfall. 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). Large areas of north-eastern NSW received much higher rainfall than the December average. In some areas, particularly in the North Coast Local Land Service (LLS) region, the anomaly was 100-400mm higher than the average. Parts of Western and south-eastern NSW also received higher than average rain totals. Elsewhere December rainfall was close to or slightly below the December average.

Much of NSW, particularly in the east, received more than 25mm of rainfall during December (Figure 2b). The highest totals occurred in the North Coast LLS region where totals ranged between 300-800mm. Lower totals (less than 25mm) were received in large areas of the Western, Riverina and Murray LLS regions. In some of these regions totals of less than 10mm were recorded.

Rainfall accumulation for 2020 was near or above average across NSW. Much of eastern NSW accumulated totals above 600mm for the year (Figure 2c). Higher totals of more than 1,000mm were received along parts of the eastern seaboard, the southern Alpine areas and in isolated districts west of the Great Dividing Range. Some eastern areas recorded annual rainfall totals above 1,400mm, while parts of the North Coast received more than 2,000mm during the year. Rainfall totals in the far west ranged between 100-400mm during 2020, though a high amount of variability remained prevalent throughout the year.

Temperature

Maximum temperatures in December varied compared to the long-term average with anomalies ranging between -2 to 1°C either side of the average (Figure 3a). The average maximum temperatures recorded in December (Figure 3b) were warmest across northern NSW (above 36°C). Elsewhere temperatures ranged between 24-33°C, while the tablelands and alpine regions experienced maximum average temperatures between 15-24°C.

Minimum temperature anomalies for December were generally 0-3°C warmer than average across most of northern and eastern NSW, however were 0-2°C cooler than average in parts of western, central and southern NSW (Figure 3c). Most of NSW experienced average minimum temperatures above 15°C during the month (Figure 3d), however parts of the Central and Southern Tablelands received lower minimum average temperatures between 6-12°C, while much of northern NSW received temperatures warmer than 18°C.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 4) indicates that plant greenness levels were close to, or above normal across large areas of NSW for the October to December period. Plant greenness levels are still variable in western and northern NSW, while low plant greenness anomalies remains evident in much of the bushfire affected areas of the Central Tablelands, South East and Alpine areas of the state.

NSW Farm Dam Survey

Please note that due to processing difficulties, the seasonal NSW Farm Dam Survey does not include December data for this edition of the State Seasonal Update. The existing data from November has been reproduced and can be used as a guide until the new data can be properly processed.

The data from the NSW Farm Dam Survey (Figure 5) indicated that farm dam levels in most central regions of the state were above 40% of capacity at the end of November. Deficiencies of less than 20% of dam capacity remained evident in parts of the Western, Murray, Riverina, North West, North Coast and Northern Tablelands Local Land Services (LLS) regions. Evaporation rates and farm water use are typically high at this time of year and should be considered where lower recent rain totals may not have replenished water losses or use.

Significant Events

The Bureau of Meteorology reports that a slow-moving low-pressure system and trough was near the coast in the New South Wales and Queensland border region from the 12-17^th December 2020. The system delivered widespread heavy rain and caused flooding for the Tweed, Clarence, Richmond/Wilsons and Bellinger rivers. Daily totals over 200mm were recorded at many sites during this period, and some sites recorded their highest daily December rainfall totals on record.

Individual drought indicators

Soil Water Index

The Soil Water Index (SWI, Figure 6) indicates the majority of NSW is currently at average or above average levels. Parts of western, northern and southern NSW continue to be experiencing below average soil water values.

Plant Growth Index

The Plant Growth Index (PGI, Figure 7) response generally mirrors the SWI with large areas of the NSW in the average category at the end of December. However, parts of the far west, south east and north east continue to experience below average plant growth values.

Rainfall Index

Rainfall accumulation during 2020 has improved the Rainfall Index (RI, Figure 8) across NSW. Much of NSW is currently in the average or above average range.

Drought Direction Index

The Drought Direction Index (DDI, Figure 9) tracks the 150-day trend of daily rainfall totals. The DDI indicates that the majority of the state shows a neutral to strong drying trend with the exception of north-eastern NSW which is displaying a strong wetting trend for 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 10 displays the CDI status for each individual Local Land Services regions to 30 December 2020. The following regional descriptions are based on data available until the end of December 2020.

Murray and Riverina regions

The Combined Drought Indicator (CDI) shows that the Riverina and Murray Local Land Services (LLS) regions continue to transition through a recovery from the 2017-20 drought event. Most of the region is currently in the Non-Drought CDI category (Figure 11) and the continuation of rainfall during 2021 will assist a long-term recovery.

The seasonal NDVI anomaly data (Figure 12) shows that the region was predominately experiencing near normal to higher than normal plant greenness levels for the October to December period. Greenness levels are slightly below average in the south-western parts of the region. The impact of the 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 that conditions steadily improved during 2020 and highlights the effectiveness of more consistent follow-up rainfall over recent months. At Moulamein, the improvement to conditions occurred later in the year due to lower rainfall consistency, especially in the winter period. Rain in late October has recently improved the indices. Follow up rainfall will likely still be required at Moulamein and Finley to maintain the improved conditions.

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

The area of the Non-Drought category of the Combined Drought Indicator (CDI) expanded across the Western Local Land Services regions in December (Figure 14). The region experienced some useful storm rainfall during the month. This will initiate and continue some relief to drought conditions across various parts of the region. Despite this, the rainfall patterns remained variable and on-ground reports continue to highlight a high degree of variation in on-ground conditions.

The NSW DPI advises that conditions remain variable in the Western LLS region. Rainfall during 2020 has begun recovery, however further rainfall is needed, particularly in areas where improvements have been more recent. Drought management continues amid hot conditions across much of the region and further follow-up rain remains a key focus to secure a longer-term transition to drought recovery.

The seasonal NDVI anomaly data (Figure 15) shows high variability in plant greenness levels across the region compared to long-term expectations for the October to December period. Some districts are experiencing well above normal levels of greenness while other districts continue to experience below normal levels of greenness (brown areas on the map). Rainfall has been lower, later or less effective in these areas.

The time series charts (Figure 16) show the individual response of the drought indices for Bourke, Ivanhoe and Wentworth. Conditions generally improved at all locations during 2020, though all three locations show variable rainfall patterns and responses in the soil water and plant growth indices. The charts highlight the importance of consistent follow-up rain for driving a longer-term response to the soil water and plant growth indices. 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

The area of the Non-Drought category of the Combined Drought Indicator (CDI) expanded across the three northern Local Land Services regions in December (Figure 17). The areas further north in these LLS regions received some much-improved rain totals during the month. This will initiate some relief to drought conditions that prevailed during 2020, though additional follow-up rain will still be required in some of these areas to secure a longer-term transition to drought recovery. Some of the rain totals were extremely high for the month, especially in parts of the North Coast LLS.

The seasonal NDVI anomaly data (Figure 18) indicates near-normal to positive greenness anomalies across much of the region for the October to December period. Plant greenness is slightly less than expected in some northern areas.

The time series charts (Figure 19) show the individual response of the drought indices for Moree, Walgett, Tenterfield and Lismore. There have been variable agronomic responses to the rainfall that was received during 2020. The drought indices have gradually improved at Walgett and Moree where the continuation of follow-up rain has maintained the recovery from drought. Lismore highlights the importance of follow-up rain. Prior to the rain received during December, follow-up rain totals have been low since February 2020. This dry period caused the agronomic indicators to plateau despite the higher rain totals received earlier in the year. Tenterfield has experienced slight improvements to the rainfall index over the last six months and continues to lag in drought recovery. The rainfall received in December will assist, however further rainfall is likely required to build upon the recent improvements. The NSW DPI continues to monitor the area closely.

Central Tablelands, Central West, Hunter and Greater Sydney regions

The Central West, Central Tablelands, Hunter and Greater Sydney Local Land Services (LLS) region continued a strong transition through drought recovery during December. Consistent follow-up rainfall since Autumn in 2020 has aided recovery in all four LLS regions, especially in Central West and Greater Sydney where recovery has been occurring longer (Figure 20). Further rainfall during the month has further strengthened recovery across most of these LLS regions.

The seasonal NDVI anomaly data (Figure 21) continues to show above average levels of plant greenness across large areas of these LLS regions. The data indicates that improvements gained from rainfall received earlier in the year have been maintained in most areas at the end of December. There has been a slight reduction in plant greenness levels in the western parts of the Central West LLS region in the last month. The 2020 bushfire impact also remain evident in parts of the tablelands.

The time series charts (Figure 22) show the individual response of the drought indices for Cowra, Condobolin and Singleton. Rainfall since Autumn 2020 has improved the indicators at all locations and shows that drought recovery remained strong throughout Spring and has been carried into Summer.

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 in the South East Local Land Services region during December. The Combined Drought Indicator (CDI; Figure 23) shows an expansion in the area of the Non-Drought categories across southern parts of the region during the month. The strong transition towards drought recovery that commenced in winter has also continued during the month in the northern parts of the region.

The seasonal NDVI anomaly data (Figure 24) shows higher than expected levels of plant greenness across much of the region for the October to December period. Some areas in the south of the region have experienced improved plant greenness levels since the November update. The areas impacted by the 2020 bushfires continued to have well below average plant greenness.

The time series charts (Figure 25) show the individual response of the drought indices at Bega, Goulburn and Cooma. The charts show the gradual improvement in conditions, however the agronomic recovery at Cooma and Bega has lagged in comparison to Goulburn. Despite improvements, the areas in the south-east would benefit from further follow-up rainfall; a longer duration of Intense Drought conditions persisted in this area later during 2020. The NSW DPI continues to monitor the area closely.

Seasonal climate outlook

Official national outlook

The official national outlook released by the Bureau of Meteorology (BoM) on 7 January 2021 indicated that February–April rainfall is likely to be close to or above average for much of Australia. Higher chances of above average rainfall are indicated in Queensland, parts of New South Wales, and the northern coast of Western Australia.

Maximum temperatures during February–April are likely to be above average for most parts of Australia's coastline, across Tasmania, and in much of Victoria and South Australia. Maximum temperatures are likely to be below average for inland parts of Queensland. Minimum temperatures for February–April are very likely to be above average across most of Australia.

NSW outlook

NSW currently has a moderate to high chance of exceeding median rainfall in the February-April period (Figure 26). The temperature outlook indicates a near equal to moderate chance of warmer than medium maximum temperatures across the state, however the probability of warmer than median maximum temperatures are higher along the coast and in parts of western NSW (Figure 27). There is also a high probability that minimum temperatures will exceed the median across the state during the next three months (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 5 January 2021. There has been little change to the Pacific Ocean sea surface temperatures in the fortnight and maybe signalling that the 2020-21 La Niña event has peaked. Despite this, the impacts associated with La Niña, such as above-average rainfall, are expected to persist across eastern and northern Australia through summer. There has also been a sharp rise in the Southern Oscillation Index in the fortnight and is currently at +18.8, well above the La Niña threshold of +7. Other atmospheric indicators including trade winds and equatorial cloudiness remain typical of La Niña conditions.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI; Figure 29) for the 30 days ending 3 January was +18.8. The Madden Julian Oscillation (MJO) and monsoon trough has been active in the Australian longitudes in recent weeks and has likely contributed to the recent increase in SOI values. The 90-day SOI value was +11.8.

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 across most of the eastern tropical Pacific Ocean, and south of the equator during December (Figure 30). The strength of warmer than average SST anomalies in the Tasman Sea decreased during December, however warm anomalies to the northwest and along parts of the east coast of Australia intensified during the month.

The latest values of the three NINO indices in the tropical Pacific for the week ending 3 January were: NINO3 −0.6 °C, NINO3.4 −0.8 °C, NINO4 −0.7 °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 1 January) shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific east of the Date Line. The strength and extent of cooler than average water has remained consistent since September with a slight weakening in November. Weak warm anomalies persist across large parts of the column depth west of the Date Line.

Indian Ocean (IOD)

The Indian Ocean Dipole (IOD) is currently neutral. The latest weekly value of the IOD index to 3 January was +0.1 °C. Most models indicate it will remain neutral through summer. IOD events are typically unable to form between December and April when the monsoon trough shifts south over the tropical Indian Ocean.

The IOD generally peaks in spring and typically has declining influence on Australian weather patterns in summer once the southern hemisphere wet season has commenced.

Southern Ocean (Southern Annular Mode – SAM)

The Southern Annual Mode (SAM) is currently strongly positive (Figure 32). It is expected to remain positive through to at least the end of January. The positive SAM event is being driven by La Niña and an exceptionally strong Antarctic polar vortex. Positive SAM during the spring to summer months typically enhances the La Niña 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 (January 2021). 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 12.