NSW State Seasonal Update - May 2021

Prepared by NSW DPI

NSW overview

Rainfall in May 2021 was below average across large areas of NSW. Despite dry conditions impacting soil surface moisture over the past eight weeks, sub-soil moisture stores position much of NSW for a productive winter and spring. However, further rain is now  important to maintain the productive spring scenario. The NSW DPI Combined Drought Indicator (CDI) shows 84% of NSW is in the Recovery or Non-Drought categories.

The dry conditions have increased concerns about drought expansion across parts of the north-east and larger areas of western and southern NSW. Variable, weak or delayed recovery from drought continues to impact these regions. Consistent follow-up rain for both cropping and pastoral activities is needed over coming months. The NSW DPI continues to monitor conditions closely.

The main 2021 winter crop sowing window continues. Sowing conditions and crop establishment has been variable due to the recent soil surface drying and increase in the frequency of frost. Earlier sown crops have had increased opportunity to utilise stored soil moisture for improved establishment.

Cooler temperatures, frost and dryness have slowed pasture growth during May. Pasture growth rates are likely to remain slow in the tablelands and areas at higher altitudes for the coming months. Rain is needed to boost pasture growth on the slopes and plains regions.

The latest Bureau of Meteorology (BoM) Seasonal Outlook indicates moderate to high chances of above median rainfall across NSW for the next three months. Global climate drivers are in a neutral state and currently forecast to remain neutral until Spring. Historically, forecast skill for the seasonal outlook is lower during autumn and can often show variability at this time of year. With increased interest in the outlook due to the current conditions, it is important to be reminded that the outlook skill improves in mid-winter.

The CDI and its individual rainfall, soil moisture and crop/pasture growth metrics are leading biophysical indices of drought. Factors affecting production and economic responses usually lag 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.

Rainfall

The rainfall anomaly data shows the difference between total monthly rainfall and the long-term average (1961-1990; Figure 2a). Most of NSW received below average rainfall with deficiencies of 10-25mm. The largest negative anomalies were along the central and north coast regions. The south-coast received above average rainfall during May. In some areas the rainfall was greater than 100mm above the May average.

Large areas of the state received less than 25mm of rain in May (Figure 2b), especially further west and across some parts of the Central Tablelands, Hunter and Northern Tablelands LLS regions. The highest rainfall totals were received in the south-east of the state (up to 300mm in isolated areas of the South Coast and Alpine regions).

Rainfall accumulation during the 2021 calendar year has been near or above average across most of NSW. The main exception is the far south-west of NSW where 2021 rainfall has been much lower than average at the end of May. Most of coastal NSW has received accumulated totals of 600 to 1600mm for the year (Figure 2c). Central areas west of the Great Dividing Range have generally received between 200-400mm. Large parts of the of Western LLS region have received less than 200mm in the year. The far south-west area has accumulated totals between 25-50mm of rain.

Temperature

Average maximum temperature anomalies were slightly above average across the majority of the state (Figure 3a). The average May maximum temperatures were generally above 15°C across NSW and cooler in NSW’s Tableland and Alpine regions (Figure 3b).

Minimum temperatures were near to below average across most of NSW (Figure 3c). Mean minimum temperatures ranged between 3-12°C, except for the high Tableland and Alpine regions that ranged between -3 to 3°C (Figure 3d).

The frost days map (Figure 3e), shows the number of days that overnight temperatures did not exceed 0°C across NSW in May. The frequency and area receiving frost will continue to increase during the transition into winter.

Normalised Difference Vegetation Index (NDVI) Anomaly

The seasonal Normalised Difference Vegetation Index (NDVI, Figure 4) indicates that plant greenness levels are close to, or above normal across most of NSW for the March to May period. Lower than normal plant greenness remains evident across some areas of south-western NSW and in central areas of the North West LLS region. The areas affected by the 2019/20 bushfires also remain evident in the Central Tablelands and South East.

NSW Farm Dam Survey

There are large areas of southern and western NSW where farm dam levels are less than 20% of capacity (Figure 5). Further east and in isolated areas of north-western NSW, dam levels are generally greater than 40% of capacity.

Soil Water Index

The Soil Water Index (SWI, Figure 6) indicates the majority of NSW is currently at average to below average levels. Large areas of southern, western and northern NSW have continued to transition into the below average category during May. This has been driven by dry April and May conditions. NSW DPI continues to monitor conditions closely across NSW.

Plant Growth Index

The Plant Growth Index (PGI, Figure 7) indicates that the majority of NSW is currently at average or below average levels at the end of April. The area transitioning into the below average category increased across large areas of western and southern NSW during May.

Rainfall Index

The Rainfall Index (RI, Figure 8) indicates that NSW is currently in the average to above average category. Parts of the Central Coast and South East Local Land Service regions are in the Extremely High category. This reflects the cumulative rainfall totals that have been received during the last 12 months.

Drought Direction Index

The Drought Direction Index (DDI, Figure 9) tracks the 150-day trend of daily rainfall totals. The DDI indicates that most of the state shows a strong drying trend. This is driven by the dry conditions during April and May. Parts of the South Coast show a strong wetting trend after high May rainfall totals.

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 10 displays the CDI status for each individual Local Land Services region to 31 May 2021. The following regional descriptions are based on data available until the end of May 2021.

Murray and Riverina regions

The Combined Drought Indicator (CDI; Figure 11) shows that large areas of the Riverina and Murray Local Land Services (LLS) regions continue to be in the Drought Affected category during May. Dry conditions have persisted during April and May, particularly further west in these regions. The dry conditions have made the 2021 winter crop sowing and establishment period challenging. Pasture productivity has also declined due to low rainfall and increased frost. The DPI continues to monitor conditions closely.

The seasonal NDVI anomaly data (Figure 12) shows that most of the region was experiencing near to or higher than normal plant greenness levels for the March to May period. Plant greenness levels are slightly lower than expected near the Victorian border in the Murray LLS region and in the west of the Riverina LLS region. The impact of the 2019/2020 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 seasonal conditions have declined since March 2021. The soil water and plant growth indices have shown a more rapid decline than the rainfall index at all locations. At Moulamein and further west, conditions are likely to be more pronounced after receiving less rainfall and minimal drought recovery than the other locations during 2020. Continued rain is needed to correct the recent decline in the soil water and plant growth indices and provide confidence of drought recovery during 2021.

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 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 Combined Drought Indicator (CDI; Figure 14) shows that large parts of the Western Local Land Services continue to be in the Drought Affected category during May. Dry conditions in April and May occurred across most of the region. The recent increase in the Drought Affected category highlights the variability of drought recovery in the region. It also highlights the importance of follow-up rain to support confidence of longer-term drought recovery. Other areas in the LLS region remain in the Non-Drought category and further rainfall would continue to support drought recovery in these areas.

The seasonal NDVI anomaly data (Figure 15) shows most of the region experiencing near to or higher than normal plant greenness levels for the March to May period. Plant greenness levels are slightly lower than expected in the far west and south-west.

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, however have dried during the last four months. The soil water and plant growth indices show a declining trend. The DPI continues to monitor conditions closely. 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

Conditions are variable across the North West, Northern Tablelands and North Coast Local Land Services regions, as indicated by the Combined Drought Indicator (CDI; Figure 17). Despite rain during 2021, there are still areas in the Drought Affected category. The Soil Water Index remains below average in many northern areas of these regions. The risk of a “false recovery” remains in some areas. Continued follow-up rain is needed for a full transition to longer-term drought recovery. The NSWDPI continues to monitor conditions closely across the region.

The seasonal NDVI anomaly data (Figure 18) indicated near-normal to above expected greenness anomalies across most of the region for the March to May period. The plant greenness anomaly remains below normal levels in parts of central and northern areas of the Northwest LLS region.

The time series charts (Figure 19) show the individual response of the drought indices for Moree, Walgett, Tenterfield and Lismore. The soil water and plant growth indices have plateaued or declined at all locations in recent months. The Non-Drought status continues to be driven by the Rainfall Index which has also plateaued since April. The NSW DPI continues to monitor the northern regions closely. 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 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, Central Tablelands, Hunter and Greater Sydney Local Land Services (LLS) regions continued drought recovery during May. Most of these regions remain in the Non-Drought CDI category (Figure 20). Given the strength of recovery during 2020, these regions remain well positioned for a productive season during 2021. However, the recent dry conditions have caused the individual indices to plateau or decline at most locations.

The seasonal NDVI anomaly data (Figure 21) continues to show above average levels of plant greenness across most of the LLS regions for the March to May period. The 2019/20 bushfire impact is still evident in parts of the Central Tablelands, lower Hunter and west of Greater Sydney.

The time series charts (Figure 22) show the individual response of the drought indices for Cowra, Condobolin and Singleton. Rainfall since Autumn 2020 improved the indicators at all locations and shows evidence of a strong drought recovery. These regions currently remain well placed for productive conditions in 2021, however there has been a recent decline in the individual indices, particularly the soil water and plant growth due to the dry April and May period. The NSW DPI will monitor this trend closely as the winter season progresses.

The Combined Drought Indicator (CDI) is a tool that monitors drought conditions across NSW. The drought categories are based on assessing the response of three drought indicators: soil water, plant growth and rainfall. The indicators track the data over the past 12 months. and shows how the indices are tracking compared to the long-term averages. The information provided in the map is aggregated to a Parish level and provides a regional assessment of conditions. Variability within and between farms is possible and this may not be reflected in the CDI map.

South East region

The Combined Drought Indicator (CDI; Figure 23) indicates that the South East Local Land Services region is in the Non-Drought CDI category (Figure 6). Some southern parts of the region recently transitioned to the Non-drought category after receiving above average rainfall in May. The trends of the individual drought indices show variability depending on location, however much of the South East LLS region remains well positioned for a productive season during 2021.

The seasonal NDVI anomaly data (Figure 24) showed near normal to higher than expected levels of plant greenness across most of the region for the March to May period. The areas impacted by the 2019/20 bushfires continued to have lower than average plant greenness levels.

The time series charts (Figure 25) show the individual response of the drought indices at Bega, Goulburn and Cooma. The charts show a recent improvement in the indices at Bega and Cooma where higher rainfall was recorded in May. The indices at Goulburn reflect a dry period in April and May and have declined.

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

An official national outlook was released by the Bureau of Meteorology (BoM) on 3 June 2021. Rainfall during the 2021 Winter is likely to be above average for northern areas of Western Australia and Victoria, as well as across most of the Northern Territory, South Australia and New South Wales. South-western parts of Western Australia are likely to experience below average winter rainfall.

Maximum temperatures for winter are likely to be above average for tropical northern Australia, south-west Western Australia and across south-eastern Australia. Minimum temperatures during winter are very likely to be above average for most of Australia, however parts of Western Australia have near equal chances of cooler or warmer than median minimum temperatures.

Note that forecast skill for the seasonal outlook is lower during autumn and can often show variability at this time of year. It is important to be reminded that the outlook skill improves in mid-winter. The Bureau of Meteorology releases a new 3-month seasonal update on a weekly basis each Thursday afternoon.

NSW outlook

NSW has moderate to high chances of receiving above median rainfall in the 2021 Winter period (Figure 26). The daytime temperature outlook indicates a near equal to high chance of being cooler than median across most of NSW (Figure 27), however, far eastern NSW has moderate chances of warmer than median daytime temperatures. There is a high probability of warmer than median overnight temperatures across the state (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 25 May 2021. The ENSO Outlook status is currently in the Inactive phase with models indicating that ENSO is likely to remain neutral for the next six months. Generally, both oceanic and atmospheric indicators are within ENSO neutral ranges. Note that the accuracy of the global climate drivers outlook tends to be lower at this time of year.

Southern Oscillation Index

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 23 May was +5.5. The 90-day SOI value was +1.5. Both are within ENSO-neutral thresholds.

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 monthly sea surface temperatures (SST) were normal to slightly cooler than average across parts of the central and eastern tropical Pacific Ocean during May (Figure 30). Warm anomalies remain around the Maritime Continent and in the waters around northern-eastern, south-eastern and south-western parts of Australia.

The latest values of the three NINO indices in the tropical Pacific for the week ending 23 May were: NINO3 −0.1 °C, NINO3.4 0 °C, NINO4 0.1 °C. All three NINO indices are within the ENSO-neutral range.

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 20 May) shows weak cool anomalies have retracted since April. Cool anomalies are currently only present near the surface of the eastern equatorial Pacific. The strength of these cool anomalies has decreased over the past four months. Warm anomalies persist west of the Date Line. These warm anomalies have also decreased in strength compared to March and April.

Indian Ocean (IOD)

The Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 23 May was −0.46 °C. Over the past two weeks, warm anomalies have strengthened in the north east of the Indian Ocean basin.  The recent warm anomalies off Western Australia may have an influence on shorter-term local weather patterns.

Most climate models expect a neutral IOD for the first half of winter, however the accuracy of IOD forecasts made during autumn are lower than at other times of the year. Model accuracy begins to improve for forecasts made during mid-winter.

Southern Ocean (Southern Annular Mode – SAM)

Recent values of the Southern Annular Mode (SAM) index are negative. These values are expected to remain negative for the next week and then increase towards neutral values in the following week. At this time of year, a negative SAM can increase rainfall over south-eastern Australia, but reduce rainfall for northeast New South Wales.

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.

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

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 (2021), Panorama Avenue, Bathurst 2795 and data which is © Commonwealth of Australia 2021, 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.