Prepared by NSW DPI Climate Unit
New South Wales (NSW) continued to experience widespread and long term drought conditions during July 2019. With the exception of parts of southern NSW, below average rainfall was the prominent feature for the month, providing no respite in ongoing poor agronomic conditions. Given the extent of long term soil moisture deficits and reliance on follow-up rainfall, it is expected that producers will continue their drought management plans as spring approaches.
July rainfall totals were generally well below average across the state. Winter crop production remains limited in northern and western NSW due to extensive planting reductions and poor early season rainfall. The persistence of long term soil moisture deficits is also placing pressure on summer crop opportunities across the state. Low July rainfall totals have increased the strain on feed availability, with cold winter conditions also adversely impacting feed levels.
In contrast, parts of southern NSW benefited from higher rainfall totals. Despite this, the totals were minimal in the context of the long term soil moisture deficits and the region remains highly dependent on follow up rainfall to maintain crop potential. The cold winter conditions and frost is also limiting feed productivity in the south, while spring feed potential also remains heavily reliant on further follow up rainfall.
The NSW DPI Combined Drought Indicator (NSW CDI) provides a general regional assessment of the complex pattern of field conditions across NSW. Overall, the CDI at the end of July shows little change from June in terms of the total area of the state affected by drought conditions. There has been another increase in the area categorised as Drought Affected (Intensifying), reflecting the lack of follow up or breaking rainfall that is required to provide longer term relief to agronomic and hydrological conditions. The CDI shows that 96.3% of NSW remains in one of the three drought categories.
The official climate outlook released by the Bureau of Meteorology (BoM) on 25 July 2019 continues to indicate a reduced likelihood of receiving median rainfall across NSW for the next three months. A positive Indian Ocean Dipole (IOD) remains the dominant feature in the forecast this month, with a positive IOD being correlated with dry conditions for central and southern Australia. The BoM also provided an updated ENSO outlook on 6 August 2019, where the El Niño status remains neutral. This current ENSO forecast is expected to be relatively unchanged late into 2019.
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.
The majority of NSW received below average rainfall throughout July. Large areas of the state received totals that were less than 60% of the July average. While isolated, the south western Riverina region was the main notable area receiving near average totals for the month. This region and isolated areas on the north coast received totals of between 25-50mm. Elsewhere totals were less than 25mm for the month. Monthly totals are shown in Figure 2 below.
July daytime temperatures (Figure 3) ranged between 18-24°C across northern NSW including the coast, with higher elevations in the north ranging between 12-15°C. In southern NSW, temperatures ranged from 12-18°C, with higher elevations in the south ranging between 3-12°C. Daytime temperatures were generally 1-3°C warmer than average across the whole state.
Overnight temperatures (Figure 4) ranged between 3-9°C across most the plains and coastal districts of NSW. Areas at higher elevations on the slopes and tablelands experienced temperatures ranging from -3 to 3°C for July. Overnight temperatures were 1 to 2°C warmer than average in the central west and southern areas of NSW, while the remainder of the state experienced warmer than average overnight temperatures ranging between 0-1°C.
Plant greenness levels continue to remain well below the long term expectations for July across NSW. Despite some technical issues with data availability for the month*, the below average greenness is reflected in the Normalised Difference Vegetation Index (NDVI) Anomaly (Figure 5) below.
NDVI is an index that provides a measure of vegetation density and condition. The NDVI anomaly is the separation of the current NDVI from the long-term average for this time of year.
*Unfortunately there are some physical limitations for data capture of the NDVI details at this time of year. This is due to the sun elevation being too low at southern latitudes across Australia during the satellite observation time. Occasionally this results in missing data, as is the case for July.
Despite some data limitations*, the dry July conditions have not made any notable improvements to farm dam levels across the majority of NSW. Figure 5a shows that surface water availability remains critical across large areas of the state with the continued requirement of extensive and consistent rainfall needed to initiate adequate runoff.
*Unfortunately there are some physical limitations for the farm water status this month. The hashing added to the map (Figure 5a) indicates areas where high data uncertainty may be expected due to the impact of low solar angle. This is a similar physical issue impacting the quality of the NDVI data for July.
The Soil Water Index (Figure 6, SWI) remains below average to extremely low across the majority of NSW. Rainfall received during July was not sufficient to improve the soil water status which remains at similar levels to the June State Seasonal Update.
There were no major improvements to the Plant Growth Indicator (Figure 7, PGI) during July due to the extent of dryness being experienced. The majority of NSW continues to experience below average to extremely low plant growth relative to the long term data.
There has been no improvement to the Rainfall Index (Figure 8, RI) since June for the majority of NSW. This highlights the dryness of conditions experienced across the state for July. This also suggests that the totals received in the areas that did experience rain for July were not large enough to strongly influence the long term rainfall deficits.
The majority of NSW experienced a drying trend during July as indicated by the Drought Direction Index (Figure 9, DDI). This provides another indication for the scale of the dry conditions experienced throughout the month.
Changes in the individual drought indicators may have occurred since this update was released. For the most current information, please visit DroughtHub.
Figure 10 displays the CDI status for each individual Local Land Services region to 31 July 2019.
The Murray and Riverina Local Land Services (LLS) regions continue to experience widespread drought conditions. The Combined Drought Indicator (CDI) shows the majority of these regions classified as being in the Drought or Drought Affected categories (Figure 11). July rainfall received in the south of the region provided some benefit, however there has been an increase in the intensification of drought conditions across the Riverina LLS region since June.
Despite some technical issues with data availability at this time of year, the monthly NDVI anomaly data (Figure 12) indicates that most of the region continues to be experiencing below normal levels of greenness. Despite rainfall improving isolated areas of the region in May, the resulting agronomic activity throughout June and July has not surpassed the long term expectations for this time of year.
The time series charts (Figure 13) showing the individual response of the drought indices for Hay, Griffith and Wagga Wagga reflect the period of beneficial rainfall occurring in May. This resulted in a positive soil water and agronomic response providing some opportunity for winter crop potential. The charts also highlight that follow up rainfall is required to maintain this potential.
The continuation of dry conditions throughout July resulted in the intensification of drought conditions for most the Western Local Land (LLS) services region. The Combined Drought Indicator (CDI) continues to show the majority of the area as being in one of the three drought categories of Drought Affected, Drought or Intense Drought (Figure 14). The recent short term signs of drought recovery in the Ivanhoe district remain heavily reliant on the continuation of follow up rainfall.
Field reports indicate that on-ground conditions remain generally poor and the NDVI (Figure 15) shows the continuation of poor agronomic conditions compared to long term expectations.
The time series charts (Figure 16) showing the individual response of the drought indices for Bourke, Broken Hill, and Wentworth reflect the variation between locations. Despite not being drought breaking, Bourke and Broken Hill experienced a positive shift in the indices during April and May. This has been short lived with the indices declining due to the lack of follow up rainfall, highlighting the importance of follow up to instil long term drought relief. Wentworth has experienced a longer period of time where the drought indices have struggled to surpass the lowest 10th percentile, indicating that there has been little if any relief to drought conditions over recent months.
Drought conditions continued to impact the entire northern area of NSW. The Combined Drought Indicator (CDI; Figure 17) shows that the entire region continues to experience drought conditions with more than half of the region now classified as being in the Intense Drought category.
On-ground conditions remain poor and this is reflected in the NDVI anomaly data (Figure 18) which remains below long term expectations.
The time series charts (Figure 29) showing the individual response of the drought indices for Moree, Walgett and Tenterfield reflect the long term trend of the indices declining and tracking in the bottom 5th percentile of the historic range. Despite a small positive rainfall shift at Tenterfield in early 2019, the rainfall effectiveness was poor as indicated by the lack of response in the soil moisture and plant growth indices. All three locations show extremely low rainfall indices for the majority of 2019 and highlights the ongoing intensity and duration of drought conditions occurring in northern NSW.
The vast majority of the Central Tablelands, Central West, Hunter and Greater Sydney Local Land Services regions (LLS) continue to experience drought conditions. The Combined Drought Indicator (CDI) shows that most of the area remains categorised in either of the Drought Affected, Drought or Intense Drought categories (Figure 20). The current nature of drought conditions remain similar from June, however another month of poor conditions in addition to the already prolonged exposure to drought conditions has continued to create difficulty as spring approaches.
The monthly NDVI anomaly data (Figure 21) indicates that the majority of the region continues to experience lower than normal levels of greenness. The lack of July rainfall and agronomic response to rainfall received in isolated areas over recent months has not surpassed the long term expectations in these regions for July.
The time series charts (Figure 22) show the individual response of the drought indices for Cowra, Condobolin and Singleton. Drought conditions have impacted all locations for an extended period of time, however does show some variation in the nature of the drought between the locations. There was a period of short term relief at Singleton, however any relief has been short lived as reflected in the declining indices due to the lack of follow up rainfall. The importance of follow up rainfall can also be observed at Cowra, where the rainfall that has been received has largely been ineffective on soil moisture and plant growth. The duration and intensity of conditions at Condobolin have been far more severe, with the drought indices all tracking below the bottom 5th percentile for the last six months.
The majority of the South East Local Land Services (LLS) region is classified as either Drought Affected (intensifying) or Drought as shown by the Combined Drought Indicator (CDI) (Figure 23). There has been little change since June and low July rainfall has extended the already prolonged duration of drought.
The monthly NDVI anomaly data (Figure 24) experienced some technical issues with data availability that is often common at this time of year. The data that is available continues to indicate that the region is experiencing below normal levels of greenness for June, and given current conditions, this is likely across the entire South East LLS region.
The time series charts (Figure 25) showing the individual response of the drought indices at Bega, Goulburn and Cooma reflects the period of beneficial rainfall occurring in May. This resulted in a positive soil water and agronomic response. Despite this, it also indicates that conditions have recently plateaued and in some instances reverted back into drought conditions (E.g. Bega). This exemplifies a false recovery and highlights the importance of follow up rainfall.
The official National Climate Outlook for August to October was released by the Bureau of Meteorology (BoM) on 25 July 2019. The rainfall outlook for the next three months indicates drier than average conditions are likely for the majority of Australia.
Both daytime and overnight temperatures for the next three months are likely to be warmer than average for much of Australia, however parts of southern Australia and northeast Queensland have a near equal chance of warmer or cooler overnight temperatures. The Bureau has highlighted a heightened frost risk as spring approaches due to dry atmospheric conditions and the likelihood of more cloud free days and nights being expected.
The main climate influences include a positive Indian Ocean Dipole (IOD) and an ENSO-neutral tropical Pacific Ocean. The positive IOD is likely to be the dominant climate driver for Australia over the next three months. In addition to the natural drivers such as ENSO and the IOD, Australian climate patterns are being influenced by the long-term increasing trend in global air and ocean temperatures.
The majority of NSW is forecast to have a lower chance of exceeding median rainfall for the next three months (Figure 26).
The historical rainfall outlook accuracy at this time of year is moderate to high for most of NSW. The exception is the far southeast corner of the state where the current forecast accuracy tends to be lower for the August to October period.
The BoM temperature outlook for August to October (Figures 27 & 28) indicates an increased chance of warmer than average daytime temperatures across all of NSW. The central west and northern regions of the state are currently forecast to have a stronger chance of experiencing above average daytime temperatures. Overnight temperatures are also predicted to have a higher chance of being warmer than average for areas in the central west, northwest and across much of eastern NSW. Elsewhere, overnight temperatures are indicated to have a near equal chance of warmer or cooler than average. As spring approaches, the Bureau has highlighted the heightened risk of frost again this month due to the increased chances of dryness with more cloud free days and nights.
The Bureau of Meteorology’s El Niño–Southern Oscillation (ENSO) assessment was released on 6 August 2019. Models indicate the tropical Pacific is very likely to remain ENSO-neutral for the remainder of 2019. All climate models surveyed by the Bureau indicate the tropical Pacific will remain ENSO-neutral through the southern hemisphere winter and spring.
The update provided on 23 July 2019 indicated that the central to eastern tropical Pacific sea surface temperatures were slightly above average, while sub-surface temperatures were close to average. Atmospheric indicators of ENSO have shown some variation, but the recent drop in the Southern Oscillation Index (SOI) is related to short-term variability in tropical weather patterns rather than a shift back towards El Niño. Cloudiness near the Date Line and trade winds remain close to average.
With ENSO playing less of a role, a positive Indian Ocean Dipole (IOD) is likely to be the dominant climate driver for Australia's weather for the coming months.
The 30-day Southern Oscillation Index (SOI) has remained near El Niño threshold levels over the past two weeks. The SOI for the 30 days ending 4 August was −8.1, with the 90-day value −9.2.
As reported on 23 July 2019, the recent fall in SOI has been related to short-lived fluctuations in tropical weather, rather than a shift back towards broad El Niño patterns.
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 (SSTs) for the week ending 4 August remain warmer than average across the central and western equatorial Pacific Ocean, but overall patterns are consistent with a neutral ENSO state. Most of the northern half of the Pacific Ocean and the southwestern quarter is warmer than average, while parts along the equator and down the South American coastline are slightly cooler than average.
SSTs are warmer than average around the east and southwest of Australia. For the remainder of the Australian coastline, SSTs are broadly close to average, with weak negative anomalies along parts of the northern and southern coastline. Also visible are the cooler than average waters to the northwest of Australia, near the Indonesian islands of Java and Sumatra. Cooler waters in this area typically occur during a positive IOD.
The latest values of the three key NINO indices in the tropical Pacific for the week ending 4 August are: NINO3 −0.1 °C, NINO3.4 +0.3 °C and NINO4 +0.9 °C. While NINO4 in the west has warmed slightly in the past fortnight, NINO3 and NINO3.4 have cooled by 0.4 °C and 0.2 °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.
The four-month sequence of equatorial sub-surface temperature anomalies (to July) shows a pattern of very weak shallow warm anomalies, and very weak cool anomalies at greater depth. This pattern has been evident, although progressively weakening, since April.
Weak positive anomalies persist across most of the top 100 m of the sub-surface, with most of this region within two degrees of average. Weak cool anomalies persist at around the 100m depth, with anomalies again mostly within two degrees of average.
The Bureau indicates that the Indian Ocean Dipole (IOD) index values have been near the threshold for a positive IOD in recent weeks. The broad pattern across the Indian Ocean has remained positive IOD-like, with warmer than average sea surface temperatures near Africa and cooler than average waters to Australia's northwest. The latest weekly index value to 4 August was +0.51°C with two of the last three weeks exceeding positive IOD thresholds.
Five of the six international climate models surveyed by the Bureau indicate positive IOD values will persist through the southern hemisphere spring. Typically, a positive IOD brings below average winter–spring rainfall and snow depths, above average temperatures, and an earlier start to the fire season for southern and central Australia.
Similar to June, the Southern Annular Mode (SAM) is forecast to trend toward negative values in mid-August, despite a positive uplift towards the end of July. In winter, a negative SAM means that the westerly wind belt is expanded further north, potentially allowing more rain-producing cold fronts to pass over southern parts of Australia.
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:
The way in which the indicators are combined to form the CDI is described in Table 2 below.
Table 2: The way in which the indicators are combined to form the CDI
Description - typical field conditions
All three indicators (rainfall, soil water, plant growth) are below the 5th percentile
Ground cover is very low, soil moisture stores are exhausted and rainfall has been minimal over the past 6-12 months.
At least one indicator is below the 5th 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 30th 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 30th 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.
All indicators are below the 50th percentile but above the 30th 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.
At least one indicator is above the 50th percentile.
Production is not limited by climatic conditions.
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), 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 (2019), Panorama Avenue, Bathurst 2795 and data which is © Commonwealth of Australia 2019, 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 Industry, Skills and Regional Development, 2019. 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 (July 2019). 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 7 Issue 7.