NSW State Seasonal Update - May 2020

Prepared by NSW DPI

NSW overview

The NSW drought event continued to weaken in May 2020 with large areas of the state in the Drought Affected category. The Autumn season has been favourable for dryland agriculture, with improved field conditions and production outlooks across large areas of the state. Much of NSW is in the early stages of drought recovery and the climatic outlook is currently optimistic for July and August. Despite this, there are regions of the state where the intensity of the drought event remains high, including parts of the far West, South East and Northern Tablelands. A full transition out of this drought event relies on widespread rainfall across NSW in the coming winter. This will continue the recovery currently being experienced in dryland farming, but also improve water storages for irrigation.

Autumn rainfall has increased confidence for the 2020 winter crop in most regions. Residual soil moisture and favourable May temperatures have assisted crop sowing and establishment. Further planting opportunities will also be available over the coming weeks.

With the winter feed gap approaching, autumn rainfall and mild May temperatures provided useful pasture growth in many regions. Spring pasture growth potential remains heavily reliant on winter rainfall increasing soil moisture levels. The first frosts of the season have been recorded in parts of the Tablelands, which can pause growth in some pastures for the winter.

Despite a favourable Autumn, conditions remain variable across NSW. Remote sensing data reflects on-ground reports of improved plant growth across much of the state in the March to May period. The data also highlights the areas where rainfall has been lower or less effective. The NSW DPI Combined Drought Indicator (CDI) showed that 90.8% of the state was in one of the three drought categories at the end of May and that winter rainfall is still needed to continue improvement.

Some regions continue to experience long-term and intense drought conditions. The far west, south east and part of the Northern Tablelands remain in Intense Drought and there has been no substantive relief to drought conditions in recent months. Conditions in most coastal regions continued to plateau due to rainfall deficits occurring in May.

While early drought recovery is underway in many regions, the situation remains complex and a ‘watch and monitor’ status is still advised. May conditions continued recovery in many areas, however the possibility that this is a ‘false recovery’ cannot be ruled out. Seasonal climate outlooks in June and July combined with a reassessment of the drought situation across the state in mid-winter are key markers for longer-term recovery.

The official Seasonal Climate Outlook released by the Bureau of Meteorology (BoM) 4 June 2020 indicates that most of NSW has near equal to moderate chances of receiving greater than median rainfall in the June to August period, though the month of June is forecast to be drier. The main global climate models remain neutral, though there are signs that the chances of rainfall may improve across south eastern Australia later in the year. Caution for both the outlook and the global climate models is still advised; the historical skill of the forecast period is low to moderate and highly variable at this time of year.

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.

*Note: the presentation format of some maps has changed in this month's edition of the SSU. New systems for map production have been developed to operate under Covid-19 work arrangements.

Drought Duration

Drought duration is an important component of drought 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 May 2020. Despite some Drought Affected areas experiencing the early stages of a 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

May rainfall was generally below the long-term monthly average across NSW as shown by the addition of a rainfall anomaly map in this month’s State Seasonal Update (Figure 3a). The map shows the difference between total monthly rainfall and the long-term average (1961-1990). Most of NSW received up to 50mm less rainfall than the long-term average for May.

Rainfall totals varied across NSW during the month (Figure 3b). Generally eastern NSW received falls of between 25 and 100mm. Areas in Western NSW and the far south east received lower rainfall totals ranging between 0 and 25mm.

Rainfall accumulation for 2020 has been near or above average for most of NSW, however areas in the far west and south east of the state continue to remain drier than average. Totals of above 400mm have been received in most areas east of the Great Dividing Range (Figure 3c), except for southern coastal regions. Central areas of NSW have received between 300-600mm, while totals further west range between 5-300mm for the year. Rainfall has positioned some regions well for recovery later in the year if follow-up rain is received.

Temperature

Daytime temperatures in May were 1-2°C below average across most of NSW (Figure 4a). The average daytime temperatures recorded in May (Figure 4b) were above 18°C across most of western, northern and coastal NSW. Warmer temperatures of above 23°C were recorded further north closer to the Queensland border and on the North Coast. Most of the Murray, Riverina and parts of the Northern Tablelands Local Land Service (LLS) regions received daytime temperatures of between 12-18°C. Temperatures in the Alpine areas were cooler between 6-12°C.

Overnight temperatures were 0-3°C below average across most of NSW during May (Figure 4c). Overnight temperature ranged between 3 and 9°C for the majority of NSW, while coastal regions were warmer between 9 and 15°C (Figure 4d). Overnight temperatures were cooler at higher altitudes and the alpine region of NSW where they ranged between -3-0°C.

The new frost days map (Figure 4e), shows the number of days that overnight temperatures did not exceed 0°C across the state during May. This map will continue to be available in the State Seasonal Update during the winter/early spring period.

Normalised Difference Vegetation Index (NDVI) Anomaly

The inclusion of a new remote sensing analysis from a collaboration between NSW DPI and Geoscience Australia (Digital Earth Australia program) for NSW has continued this month. The interim (beta) product (Figure 5) is a seasonal overview of the Normalised Difference Vegetation Index (NDVI) and replaces the monthly product used in previous editions of the State Seasonal Update.

The current analysis is for the three months from March to May (May 22). The analysis indicates that drought conditions have weakened substantially in many areas of the state during Autumn. Plant greenness levels are closer to normal values across much of the state and are above normal in many central and eastern areas of NSW. Despite this, the analysis highlights regions that are still experiencing below normal levels of greenness for the Autumn period. 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.

A number of technical factors need to be considered when considering the new 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, contrasting to the 1km resolution of the previous product.
• There is a processing lag in Landsat data that can be up to ~3-4 weeks
• The visible and infrared bands are used to calculate NDVI, which then calculates vegetation greenness. This is a useful measure of vegetation density and plant health.

Clouds and smoke can sometimes obstruct observations which can cause gaps in the NDVI data or banding in the available imagery.

NSW Farm Dam Survey

There is currently a delay in processing the latest data for the NSW Dam Survey. The data from the April State Seasonal Update indicated that rainfall in March and April has improved farm dam levels in many central and north-west areas of NSW (Figure 6). Areas in eastern NSW had slightly improved dam levels compared March, while there were still large areas in the south and far western regions showing very low farm dam levels.

Short-term Soil Water and Plant Growth

The short-term response of soil water and accumulated pasture growth to the recent rainfall is shown in Figure 7a and Figure 7b. The average soil water recharge over the past 30 days indicates that parts of central NSW and south towards the Victorian border are showing a stronger response to recent rainfall. A similar trend is indicated for accumulated pasture growth over the last 30 days in these regions.

Soil Water Index

The Soil Water Index (SWI, Figure 8) remains below average across most of NSW. The index has remained relatively stable since the May 2020 State Seasonal Update. Rainfall accumulation during 2020 has helped improve the soil water index in many regions compared to the same time in 2019.

Plant Growth Index

The Plant Growth Index (PGI, Figure 9) remains below average to extremely low across most of NSW at the end of May. Despite large improvements since the start of 2020, the improvements to the index remain slow with little change in the spatial distribution of the data since the end of April.

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 April State Seasonal Update.

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 neutral to drying trend which is largely a result of insufficient rainfall in May relative to longer-term rainfall accumulation. A stronger drying trend is currently occurring across much of the north east and areas east of the Great Dividing Range. Parts of western and southern NSW show a weak wetting trend due to the nature of rainfall patterns over the last five months.

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 May 2020. The regional descriptions are based on data available until the end of May 2020.

Murray and Riverina regions

Rainfall during Autumn has improved conditions across the Murray and Riverina Local Land Services (LLS) regions. The Combined Drought Indicator (CDI) shows most of the region is still in the Drought Affected CDI category (Figure 13), however the CDI data is showing an improvement in conditions with much of the region in the early stages of drought recovery. The region is well positioned to transition towards recovery if a consistent rainfall pattern develops during the 2020 Winter. May conditions were positive for winter crop sowing activities and provided a flush of pasture growth prior to the winter feed gap.

The seasonal NDVI anomaly data (Figure 14) has shown improvements since the April State Seasonal Update. Much of the region is experiencing normal to higher than normal plant greenness for the March to May 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 and Temora. The indices show that conditions are transitioning towards a possible drought recovery later in the year if follow-up rain persists during the winter. The NDVI data shows that the rainfall has largely been effective and has improved on-ground conditions.

Western region

Autumn rainfall improved conditions in many parts of the Western Local Land Services region (LLS), however there is still a large degree of variability in on-ground conditions. The Combined Drought Indicator (CDI) shows that most of the region is still in one of the CDI drought categories (Figure 16). Some areas in the Drought Affected category are in the early stages of drought recovery. Despite this, the transition towards recovery remains slow and consistent follow-up rain is critical to longer-term prospects of a sustained recovery.

Despite the drought weakening in some areas of the Western LLS region over recent months, there are still large areas in the region that have not yet had relief, especially further west. These areas require an effective rainfall event to initiate a weakening of drought conditions. The relatively dry May rainfall pattern provided little if any relief in these areas.

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 March to May period. The data highlights that rainfall totals have been low or ineffective in many parts of the region over recent months, while in other areas the rainfall has provided very a positive plant growth response.

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.

North West, Northern Tablelands and North Coast regions

Despite rain during 2020, the majority of the North West, Northern Tablelands and North Coast Local Land Services (LLS) regions continue to be in one of the three Combined Drought Indicator (CDI) drought categories (Figure 19). The area of Drought and Intense Drought categories declined during May and large areas in the Drought Affected category are in the early stages of drought recovery. Follow up rainfall will be needed to sustain improvements longer-term.

While the CDI shows varying levels of drought intensity across these regions, the remote sensing satellite data shows encouraging levels of plant greenness for the March to May period. The seasonal NDVI anomaly data (Figure 20) indicates positive anomalies across much of the region for the period. This indicates that the recent rainfall has been extremely effective for improving pasture and on-ground conditions during autumn. However, the rain has not been substantial enough to change the longer-term deficit in conditions tracked by the CDI. The drought indicators examine the last twelve months relative to a long-term comparison in the region at this time of year. To alleviate the long-term deficits further rainfall will be needed during winter to recharge soil water levels so that optimal growth can occur during Spring.

The time series charts (Figure 21) showing the individual response of the drought indices for Moree, Walgett and Tenterfield reflect the long-term trend of the drought indices tracking in the bottom 5th percentile of the historic range. Despite rain in 2020, the improvement to the indices have slowed or plateaued in recent months. The time series chart for Lismore illustrates an example of a region that transitioned out of drought into the Recovery CDI category and then quickly reverted back to the Drought Affected category. Comparing the time series, the drought event at Lismore has been shorter and less intense than the other locations at Walgett, Moree and Tenterfield. This initially led to a faster recovery from drought but also highlights the importance of follow-up rainfall despite the high amount of rain received earlier in the year around Lismore.

Central Tablelands, Central West, Hunter and Greater Sydney regions

Rain has weakened drought conditions substantially in many areas of the Central Tablelands, Central West, Hunter and Greater Sydney Local Land Services (LLS) regions during autumn. While most of the regions are still categorised in one of the three Combined Drought Indicator (CDI) drought categories (Figure 22), many of the Drought Affected areas are experiencing a transition towards a longer-term drought recovery. These regions will be well placed if favourable conditions occur during winter.

The seasonal NDVI anomaly data (Figure 23) indicates a general positive response to rainfall during autumn. The remote sensing satellite data currently shows above expected levels of plant greenness across large areas of these LLS regions for the March to May period. 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 the region 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 recent rain has improved the indicators in recent months. Cowra and Condobolin currently continue a positive but slow transition towards drought recovery. Conditions at Singleton have plateaued due to drier conditions more recently. In all cases further rain is required to sustain a longer-term drought recovery.

South East region

Autumn rainfall has improved conditions in many northern areas of the South East Local Land Services (LLS) region. In contrast southern areas have remained dry and had little relief. The southern areas remain in the Intense Drought CDI category during May (Figure 25) and are now in a period of slow plant growth rates with the onset of the winter feed gap. Southern areas require consistent winter rainfall to replenish long-term soil moisture deficits for potential relief in Spring. Many areas in the north of the region are well placed for a longer-term drought recovery if favourable conditions are received during winter.

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 during the autumn. 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. They show a large degree of variability between locations. Goulburn has shown the greatest improvement of the indices during autumn and continues a positive but slow transition towards a possible drought recovery later in the year. All locations show the importance of follow up rainfall for sustaining any improvements to the indices longer-term.

Official national outlook

The latest official national outlook was released by the BoM on 4 June 2020. The outlook indicates that the June to August period is more likely to be wetter than average for northeast SA, western NSW, and scattered parts of southern Queensland. However, coastal southeast SA, southwest Victoria, northern Australia and most of Tasmania are likely to be drier than average.

The central and eastern tropical Pacific Ocean is likely to cool over the winter months, establishing a La Niña-like pattern. Warmer than average waters are likely in the eastern Indian Ocean. In the shorter-term, higher pressure systems are likely to dominate southern Australia during the first half of June.

Daytime temperatures during winter are likely to be warmer than average across most of Australia, except southern SA, southwest NSW and western Victoria, which have roughly equal chances of warmer or cooler winter days. Winter nights are very likely to be warmer than average across most of the nation.

NSW outlook

Most of NSW currently has a near equal or chance of being wetter or drier than median in the June to August period, with higher chances of rainfall predicted for July-August than June. Parts of western and north east NSW have a slightly higher probability of receiving higher than median rainfall (Figure 28). The historical skill for the forecast period is low for large areas of western and southern NSW, including the south east coastal area. Elsewhere the historical skill is moderate to high including north east NSW and some central parts of the state.

The BoM temperature outlook for June to August (Figure 29) indicates daytime temperatures have an increased likelihood of being above median for most of eastern NSW. Daytime temperatures further west have near equal chances exceeding the median. Overnight temperatures have a strong likelihood of being above median across NSW (Figure 30).

Climate drivers

El Niño–Southern Oscillation (ENSO)

The Bureau of Meteorology’s (BoM) El Niño–Southern Oscillation (ENSO) Outlook was released on 26 May 2020. Key indicators of ENSO, such as the Southern Oscillation Index (SOI), trade winds, cloudiness near the Date Line and sea surface temperatures in the tropical Pacific Ocean, generally persist at neutral ENSO levels. However, sea surface temperatures across the tropical Pacific Ocean have cooled over the past several weeks. This has been supported by recent cooling of tropical Pacific sub-surface sea temperatures.

While a neutral ENSO is likely for the southern hemisphere winter, some model outlooks suggest a La Niña-like state will develop in the tropical Pacific Ocean during spring. Currently, three of the eight models reach or exceed La Niña levels by early to mid Spring.

The Bureau's ENSO Outlook currently remains at Inactive. However, if recent cooling at both the surface and beneath the surface of the tropical Pacific Ocean persists, and any more models suggest La Niña-like conditions in spring, the ENSO Outlook could shift to La Niña Watch over coming months.  La Niña events are generally associated with above-average winter-spring rainfall and cooler temperatures in eastern Australia.

Note that ENSO predictions made during autumn tend to have lower accuracy than predictions made at other times of the year. This is because the ENSO has a greater sensitivity to random weather factors at this time of year.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 24 May was +1.8. The 90-day value was −2.3. Both values are well 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)

Sea surface temperatures (SSTs) for the week ending 24 May have cooled compared to two weeks ago. Cooling has now been observed across the central and eastern tropical Pacific for the past 5 weeks. Ocean temperatures are now cooler than average in parts of the eastern half of the equatorial Pacific Ocean, while some parts of the far east and far west of the equatorial Pacific remain warmer than average. Much of the central tropical Pacific SSTs are close to average for this time of the year.

SSTs remain slightly warmer than average around northwest Western Australia, and along parts of the east coast of Australia.

The latest values of the three key NINO indices in the tropical Pacific for the week ending 24 May were: NINO3 −0.2 °C, NINO3.4 −0.3 °C and NINO4 +0.1 °C. All NINO indices have cooled over the past fortnight, with NINO3 and NINO3.4 cooling by a significant amount (0.4 °C and 0.5 °C respectively).

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 sub-surface temperature anomalies (to 21 May) shows cooler than average waters extend in a band across most of the equatorial Pacific, between about 100 and 200 m in the western to central equatorial Pacific and rising to a depth of around 50 m at the eastern edge of the equatorial Pacific.

In the western equatorial Pacific weak warm anomalies persist in the top 150 m, but have decreased in strength and extent compared to April.

Since January, warm anomalies in the western equatorial Pacific near the surface have decreased, while the pattern of cooler anomalies at depth has strengthened.

Indian Ocean

The IOD is currently neutral. Most international climate models surveyed by the Bureau suggest the development of a negative IOD from the middle of the southern hemisphere winter. However, each of the models show a broad spread of likely scenarios between the neutral IOD and negative IOD range, and more recent model outlooks having slightly lower likelihoods of negative IOD. A negative IOD typically brings above average winter–spring rainfall to southern Australia.

Note the accuracy of IOD forecasts is low for forecasts made during the Australian autumn, with accuracy improving in winter. The IOD currently has a greater sensitivity to random synoptic patterns causing the forecasting skill to be lower.

Southern Ocean

The Southern Annular Mode (SAM) is currently positive and forecast to remain positive for the coming two weeks. Despite this, it isn't expected to have a significant effect on rainfall during this time due to interactions with other climate drivers and local weather conditions.

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: 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.