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Droughts in Australia and their Management
Dr Dasarath (Jaya) JayasuriyaA/Deputy Director Climate and WaterAustralian Bureau of Meteorology
Expert Group meeting on Hydrological Drought Indices September 2011, Geneva, Switzerland
Presentation outline
• Drought in historical context
• Recent Australian drought (1997-2009)
• Wet conditions – 2010– Rainfall, water storages, NDVI, soil moisture
• Approach to managing drought
• Hydrological drought indices
• Summary
Historical context - Australia
• Up until 1989, official (& public) view was that drought was a natural disaster
• Relief was via State Governments, and increasingly, the national Government. Often on an ad hoc basis.
• In 1989-early 1990s, official view changed– Drought should be viewed as a natural part of environment,
– Water resource managers and farmers should adopt a risk management approach
• In July 1992, a National Drought Policy was developed
1996-2010 rainfall deficienciesImpact on population centres
Recent Drought Situation
• Very high rainfall in NE, E, SE Australia• South-west of WA lowest rainfall
Current drought service: rainfall maps
• maps of 1, 3, 6, 9, 12, 18, 24, 36 months and wet season for ‘drought’, deciles, percentages etc
Gibbs and Maher 1967 Rainfall Deciles as drought indicators
Seasonal Rainfall Outlook: August to October 2011
Impact of La Niña event
Dam storages - Melbourne
• Melbourne storages (SE Australia) - Exceptionally wet 2010-11 lifts storage fro 36% to 60%
Dam storages - Perth
• Now only 30% full• Compared to 27% 2010• Steady increase - July 2011• Lowest inflow in 2010• Only 16GL
Yearly Streamflow for Major Surface Water Sources - IWSS
0
100
200
300
400
500
600
700
800
900
1000
Annual Total1911 to 1974 av (338 GL)1975 to 1996 av (177 GL)1997 to 2010 av (101 GL)2001 to 2010 av (83 GL)
Note: A year is taken as May to April
Normalised Difference Vegetation Index: July 2011
Soil moistureWeek ending 14 Aug 2011
CSIRO, http://www.eoc.csiro.au/awap/
Upper layer Lower layer
Urban sector approach
• Use of water restrictions (different levels with increasing severity L1 to L4)
• Based on water storage levels
• Pre cooked operating rules to meet increasing demands (function of population)
• Use of HDI sparse, except experimental and for internal consumption by management
Rural irrigated agricultural sector
• Clear water entitlements (say 300GL)
• Annual allocations determined based on storage levels and forecasted inflows (may get 80% of 300GL)
• Tradable water entitlement regime
• Competitive water market– (water move - https://www.watermove.com.au/Default.aspx)
• Use of HDI patchy, inconsistent and adhoc
Rural run of river irrigators and ecological services
• Restricted supply based on low flow characteristics
• Basic ecological services provided (survival flows) and the remainder rationed equitably
• The environment is often the looser (non voter and no voice)
• Some ecological assets need droughts (with less flow allocated) to regenerate certain assets (the Growling Grass Frog)
Bureau’s role in assisting drought management (1)
• Monitoring Australian climate, including rainfall deficiencies, weekly updates, NDVI, etc
• Drought statements, weekly rainfall updates
• Seasonal Climate Outlooks
• New water information products– Water storages, soil moisture, streamflow forecasts, etc
• Advice to Governments, industry and the public
• www.bom.gov.au/climate/drought/
Bureau’s role in assisting drought management (2)
• Improving understanding and predictability of Australian droughts through R&D, e.g.– Develop improved global climate models and
statistical prediction systems
• Seasonal forecasts (weeks to seasons)
• Longer-term predictions
– Better understand the role of climate variability and climate change in recent rainfall trends
– Better understanding of decadal climate variability
Indices used in Australia
• In Australia: ADI, SPI and SWSI in Yarra River in Victoria- Management of water resources
• SPI, SWVI, NDVI: in Murray-Darling Basin, Remote sensing
• PDSI – climate modelling, continental scale, 2051-2100
• The Rainfall Deciles-base Drought Index and Soil-Moisture Deciles-based Drought Index – climate modelling B1, A1F1, CSIRO Mk3, 2030
• PDSI, Bhalme-Mooley Drought Index (BMDI), Surface Water Supply Index and Rainfall Deciles – Melbourne water supply planning
• KBDI and Soil Dryness Index (SDI) for predicting forest fire danger
Summary
• There is confusion about the type, value and use of drought indices
• All types of indices are used and sometimes, misused
• The knowledge is patchy and there is no agency responsible for (or taking the leadership) for forecasting drought conditions. BOM is developing a business case
• Stakeholders remain disconnected from some of the climate products available
• Individual agencies use fit for purpose HDI, mostly internal consumption or research
