NSW State Seasonal Update - March 2018

The NSW Combined Drought Indicator (CDI; see Table 2 for more details) has the majority of NSW under Drought Watch or Drought Onset conditions (Figure 1) as of 31 March 2018. Areas particularly affected include the Central West and Central Tablelands Local Land Services (LLS) regions. Parts of Western, North West, Riverina, Greater Sydney, Hunter and northern parts of the South East LLS regions are also in Drought Onset.

During March, conditions have continued to decline with Drought expanding in the Hunter, Greater Sydney, South East, North West and Central West LLS regions. In addition to these regions, parts of the Central Tablelands have also entered Drought. The region in Drought in the Western region remains stable.

Areas in Non-Drought and Recovering contracted during March, particularly in the Murray, Riverina, Northern Tablelands and North Coast LLS regions.

The NSW Department of Primary Industries (DPI) has been monitoring developing drought in the Hunter and Central Tablelands LLS regions and on the western slopes for some months. On-ground indicators highlight that the pasture base is in very poor condition in these areas. Despite good falls of rain in parts of the north east Hunter, this area remains in Drought Watch, while the western area that missed the high rainfall remains in Drought.

With the expansion of the area under Drought Watch in March, and the main sowing time approaching for winter crops, DPI is continuing to monitor agronomic indicators like stored soil moisture very closely.

During March, technical difficulties were encountered with Bureau of Meteorology climatic data. This affected the quality of the output produced by the Enhanced Drought Information System™ including the Combined Drought Indicator, individual drought indicators and rainfall and temperature outputs.

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.

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

Rainfall

Rainfall totals were below average across much of NSW during March, although heavy rainfall did occur in areas of the Hunter valley and mid-north coast (Figure 2). Rainfall ranged from 5 to 100 mm across most of the state and increased towards the east. Large areas of Western, Central West, Riverina and Murray LLS regions received rainfall of less than 10 mm. The southern half of the North Coast and north-east of the Hunter LLS regions received high rainfall in March, from 200 mm to above 300mm in some areas.

Normalised Difference Vegetation Index (NDVI) Anomaly

The monthly NDVI anomaly data provided by the Bureau of Meteorology indicates that lower than normal greenness extended across most of NSW during March (Figure 3). Significantly lower than normal greenness was evident across areas of the Hunter, Greater Sydney, North Coast, Central Tablelands, North West, Central West and Western LLS regions. Parts of the North Coast and South East LLS regions experienced a contraction in the area of above average levels of greenness between February and March as conditions continued to deteriorate in these regions.

Temperature

Temperatures were warmer than average across the whole state during March, particularly in areas of central NSW and the Greater Sydney and South East LLS regions.

Most of inland NSW had average daytime temperatures of over 30°C during March while in eastern NSW, temperatures ranged from 18-30°C (Figure 4). Average overnight temperatures ranged between 12-24°C across most of NSW (Figure 5). Parts of the Northern Tablelands, Central Tablelands, eastern Riverina and Murray and the South East LLS regions recorded average overnight temperatures of between 6-12°C, with parts of the alpine areas recording average overnight temperatures of between 3-6°C.

Extreme events

From 21 March, a coastal trough combined with a strong high pressure system over the Tasman Sea and resulted in high intensity rainfall across areas of the Hunter valley and mid-north coast.

Several sites across the Hunter valley, mid-north coast and Sydney basin received record daily or total rainfall during March. Other sites, including areas in the central west, southern tablelands and south west slopes received their lowest March rainfall on record or their lowest rainfall for the last 20 years.

Individual drought indicators

Rainfall Index

The Rainfall Index (RI, Figure 6) indicates below average to extremely low rainfall occurred over the majority of Western, Central West, Central Tablelands, Hunter, Greater Sydney, North West and Northern Tablelands LLS regions over the last 12 months. Eastern and northern areas of the South East region also received below average to extremely low rainfall for the period. Most of the Murray, North Coast and large parts of the Riverina LLS regions received average rainfall, with isolated pockets of above average rainfall in the north of the North Coast, Murray, Riverina and southern parts of Western LLS regions.

Soil Water Index

The Soil Water Index (SWI, Figure 7) indicates that stored soil moisture over the last 12 months was extremely low across the Central West, Central Tablelands and Greater Sydney LLS regions and large parts of Riverina, North West, South East and Hunter LLS regions. In the Western LLS region, the soil moisture levels were extremely low across large areas of the east, areas between Ivanhoe and White Cliffs and between Broken Hill and Packsaddle. Soil moisture levels continued to be below average across the rest of NSW, except for limited areas of Western, Murray, Northern Tablelands and South East LLS regions which were near average. The majority of the North Coast LLS region had near average soil moisture levels.

Plant Growth Index

The Plant Growth Index (PGI, Figure 8) for the 12 months to March indicates most of NSW experienced below average growth. Extremely low growth occurred across areas of the Hunter LLS region, much of Greater Sydney, Central Tablelands, Central West, the central areas of the Riverina, the western and south eastern areas of North West and northern areas of the South East LLS regions. Areas of the Western LLS region also experienced low growth. Areas of near average growth were present across parts of the North West, Northern Tablelands and North Coast, southern areas of the South East and parts of the Western and Murray LLS regions.

Drought Direction Index

The Drought Direction Index (DDI, Figure 9) to 31 March shows a drier trend across most of inland and southern NSW. This indicated that there has been low rainfall over the last three months in these areas, and it will take one to two months of average to above average rainfall (or extremely high rainfall) to recover from this trend. The majority of North Coast, Hunter and Greater Sydney LLS regions are currently showing a wetter trend.

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

The following figure (Figure 10) displays the CDI status for each individual Local Land Services region to 31 March 2018..

Murray and Riverina regions

The Combined Drought Indicator (to 31 March 2018) indicated that that the majority of the Murray and Riverina LLS regions are now in Drought Watch.  Areas that were previously in Non-Drought in the central Murray, near Wagga and Lockhart and in the far east of Riverina LLS region have declined to Drought Watch. The area in Drought Onset near Griffith and Narrandera has expanded northwards (Figure 11).

The monthly NDVI anomaly indicates a decline in greenness across most of the region during March. Most of the region experienced below normal levels of greenness for the month, with areas north of Griffith and Narrandera being the most severely impacted (Figure 12). Compared to February 2018, areas of normal to slightly above normal greenness have contracted this month, particularly in the far eastern reaches of the region.

Western region

The Combined Drought Indicator (to 31 March 2018) indicated that most of the Western LLS region remained in Drought Watch. There was a slight contraction of the area in Drought Onset to the north of Broken Hill and near White Cliffs, and a slight contraction in the area in Drought to the north of Broken Hill. The area Recovering near Tilpa expanded slightly, and the area in Non-Drought in the south remained much the same. There was however an increase in the area in Drought Onset in the east of the region, which now extends from Euabalong, Nymagee and Cobar to Brewarrina. A small area is also now in Drought to the north of Cobar (Figure 13).

The monthly NDVI anomaly indicates that greenness remained well below normal across the majority of the Western LLS region during March. A slight improvement occurred in the far west near Tibooburra, White Cliffs, Broken Hill and Menindee, although conditions were still below average (Figure 14). Patches of slightly above average greenness near Hillston contracted during the month.

North West, Northern Tablelands and North Coast regions

The Combined Drought Indicator (to 31 March 2018) indicated that most of the regions are now in Drought Watch, with an increase in the areas in Drought Onset between Walgett and Pilliga and near Quirindi, Murrurundi, Tamworth and Manilla. The areas Recovering and in Non-Drought have declined, with most areas of the Northern Tablelands and North Coast LLS districts now in Drought Onset. Some areas in Recovering and Non-Drought remain in the North Coast LLS region, particularly in the north (Figure 15).

The monthly NDVI anomaly indicated a decline in greenness across region during March (Figure 16). The extent of the area with below average levels of greenness continues to expand, most noticeably in the mid to southern parts of the North Coast, between Walcha and Tamworth, across the central and eastern parts of the North West and to the south of Quirindi.

Greenness across the northern half of North Coast remained near-average, with areas in the south declining from near-average to below average. The Northern Tablelands suffered the greatest decline, shifting from slightly above average to below average, with areas in the north west near Inverell and the south west near Walcha showing the lowest greenness. The North West region remained below average, with areas of the lowest greenness between Warialda and Boggabilla, between Warialda, Manilla and Narrabri, between Quirindi and Premer and near Tamworth (Figure 16).

Central Tablelands, Central West, Hunter and Greater Sydney regions

The Combined Drought Indicator (to 31 March 2018) indicated that conditions continued to decline and the region is predominantly in Drought, Drought Onset or Drought Watch (Figure 17). The area in Drought now extends across the west of Hunter LLS region, the central and southern parts of Greater Sydney LLS region and spans across the Central Tablelands and Central West LLS regions between Blayney and Dubbo and south to Parkes. An area to the west of Coonabarabran has also transitioned into Drought. A small area in the Hunter, to the south of Forster, is in Non-Drought or Recovering.

The monthly NDVI anomaly indicates continued low levels of greenness across most of the region (Figure 18). Although areas in the Hunter and Greater Sydney LLS regions showed slightly improved greenness since February due to storm rainfall events, they are still well below average. The Central Tablelands and Central West LLS regions continued to exhibit declining levels of greenness, most notably to the north and west of Orange and in parts of the far west of the Central West LLS region.

South East region

The Combined Drought Indicator (to 31 March 2018) indicates that conditions continued to deteriorate across the South East LLS region with the majority of the area in Drought, Drought Watch or Drought Onset (Figure 19). The area in Drought now extends across a greater area of the north east of the region including areas surrounding Nowra, Mittagong, Moss Vale and Wollongong. Areas across the north of the region extending from Taralga to Bigga and Tuena are in Drought Onset, as are areas from Marulan to Tarago, Nerriga, Braidwood and Captains Flat. An additional area of Drought Onset is in the far south east of the region. Areas in the south of the region which were previously in Non-Drought or Recovering have contracted and now extend from Bega to Cobargo, Bodalla and Moruya as well as between Dalgety to Jindabyne and west of Cooma.

The monthly NDVI anomaly indicates that the region ranges from slightly below through near-average to slightly above average levels of greenness (Figure 20). The northern half of the South East LLS region has experienced a slight improvement in conditions during March, while greenness levels have generally declined across the southern half of the region.

Official national outlook

The official national climate outlook for April to June issued by the Bureau of Meteorology on 29 March 2018 shows that parts of the tropical north, eastern Victoria, Tasmania and southeast NSW are likely to be wetter than average over the next three months. Elsewhere, there are near-equal chances of a wetter or drier than average three months.

April to June daytime temperatures have an increased likelihood of being warmer than average for areas of south east Australia and northern WA, and cooler than average for much of the tropical north. The rest of Australia has a near-equal chance of a warmer or cooler than average daytime temperatures over the next three months.

Overnight temperatures have an increased likelihood of being warmer than average for the southern parts of Australia, but are likely to be cooler than average in the north.

It is important to note that forecast skill is low at this time of year, during the Southern Hemisphere autumn.

NSW outlook

For New South Wales, the rainfall outlook for April to June indicates that there is a near-equal chance of drier or wetter than normal conditions across most of NSW. There is an increased chance of wetter than normal conditions across areas of the south east of the state, including areas of the south coast, areas of the southern highlands, the Monaro and the alpine areas (Figure 21).

The temperature outlook indicates that there is a near-equal chance of cooler or warmer than normal daytime temperatures across most of the state. Overnight temperatures have an increased likelihood of being warmer than normal across areas of the south and west of the state. The highest likelihood of warmer overnight temperatures is in the south east, including areas of the Monaro, south coast and alpine regions. For the remainder of NSW, there is a near-equal chance of cooler or warmer than normal overnight temperatures (Figure 22 & Figure 23).

Overall, global climate models favour a near-neutral outlook for rainfall for NSW during April to June, with two models suggesting a wetter than normal outlook. They are almost equally split between a generally neutral and warmer than normal outlook for the period, with one model suggesting cooler than normal conditions (Table 1). It is important to note that forecast skill is low at this time of year, during the Southern Hemisphere autumn.

Model Ensemble

Table 1: Overall NSW outlook – number of major climate models in each general category (as at 2018)

Climate drivers

ENSO

Indicators for the El Niño Southern Oscillation (ENSO) remain at neutral (as at 27 March 2018). Most climate models suggest a neutral outlook into winter, with little sign of El Niño or La Niña developing in the coming months. The sea surface temperatures resulting in the weak La Niña event are gradually warming, with further warming expected into winter. However, other indicators have been slow to return to neutral.

Southern Oscillation Index and other indicators

The SOI has been highly variable during summer due to the passage of tropical weather systems (including tropical cyclones) and the late start to the monsoon season. The 30-day SOI value is currently above normal levels and the 90-day SOI is within the neutral range (the 30-day value was +10.8 as at 2 April, Figure 24, and the 90-day value was +4.2). During summer, the 90-day SOI is more reliable.

Cloud levels at the junction of the equator and the International Date Line still show some influence from the weak La Niña event. They were below average during March after being above average during February.

Trade winds reversed in the western equatorial Pacific during February due to the passage of a strong Madden-Julian Oscillation, which hastened the end of the La Niña event. During March, the trade winds strengthened across the central and eastern-central Pacific, but are currently (as at 25 March) at near average levels.

Sea surface temperatures

Monthly sea surface temperatures anomalies (SST, Figure 25) remain cool across the central and eastern equatorial Pacific, but are within the Bureau of Meteorology’s neutral range (between -0.8 and +0.8) in the NINO3 and NINO3.4 regions. Temperatures are near-average to slightly above average in the western equatorial Pacific. A large area of warmer than normal surface water in the south Pacific extends from the south eastern and southern Australian coastline to New Zealand. However, the strength of these anomalies has decreased.

Sea Sub-surface Temperatures

A warm sub-surface anomaly developed in the western equatorial Pacific during February, and has moved eastwards over the last few months into the eastern-central Pacific. The extent and temperature of the anomaly was enhanced by the passage of a strong Madden-Julian Oscillation during February, and a resulting reversal of trade winds. The passage of the warm anomaly eastwards has greatly decreased the extent of the cool anomaly in the central and eastern Pacific (Figure 26).

Indian Ocean

The Indian Ocean Dipole (IOD) currently remains neutral (as at 1 April 2018). IOD events do not commonly form between December and April due to the onset of the monsoon season.

There are early indications from some climate models that a negative IOD event might develop during winter, although model predictive skill remains low at this time of year. A negative IOD event increases the chances of above normal rainfall during winter and spring across southern and much of western and central NSW.

Southern Ocean

The Southern Annular Mode (SAM) is currently weakly to moderately negative (as at 3 April 2018). After a short period at weakly negative, the outlook is for SAM to remain weakly negative into mid-April then to return to near neutral to weakly positive.

With the warm sea surface temperatures to the south and east, a more strongly positive SAM during the autumn may increase the likelihood of wetter conditions across eastern NSW. However, a positive SAM indicates the contraction of westerly winds towards Antarctica, resulting in weaker than normal westerly winds and higher pressures over southern Australia. During winter, this is generally less favourable for rainfall across inland NSW.

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 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 moisture, 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.

More services from EDIS are scheduled for release over the coming months including a seasonal conditions self-reporting application.

The way in which the indicators are combined to form the CDI is described in Table 2 below.

Table 2: Description of the Combined Drought Indicator framework

Acknowledgments

The NSW State Seasonal Update is provided each month by the NSW DPI Climate Unit, which is part of the Livestock Systems Branch in DPI Agriculture.

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) and NSW Department of Primary Industries.

Maps in this document contain data which is © Spatial Services – NSW Department of Finance, Services and Innovation (2018), Panorama Avenue, Bathurst 2795 and data which is © Commonwealth of Australia 2018, 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. Outlook information was up to date as at 29 March 2018.

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 Industry, Skills and Regional Development, 2018. 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 (April 2018). 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 6 Issue 2