Chapter 3 Climate Applications and Services

Climate Applications > Water Management

Climate variability is the main factor impacting on the availability and reliability of water resources. Improved understanding of the processes linking rainfall, evaporation, soil moisture, groundwater and surface water rely heavily on long time series of hydrological or climate-related data. Long time series also underpin the riskbased management of water resources.

Policy and Coordination

Management of Australia’s water resources is the responsibility of the State and Territory Governments. National coordination of resource management policy is through the Natural Resource Management Ministerial Council (NRMMC) and its underpinning structure of committees. The Land, Water and Biodiversity Committee of the NRMMC and the Science and Technology Network of the Australian National Commission for UNESCO have been the main avenues for the coordination of Australia’s participation in international aspects of water management. In particular, activities of the International Hydrology Programme (IHP) of UNESCO and the Hydrology and Water Resources Programme (HWRP) of WMO have been coordinated through these mechanisms.

Hydrological Data

Extensive hydrological observing systems are operated and maintained by the State and Territory based water agencies in support of water resource management. These systems are discussed in more detail in Chapter 2. The publication Australian Water Resources Assessment 2000 (AWRA) used the observations from these systems to define the extent, quantity, use and quality of Australia's water resources, as part of the National Land and Water Resources Audit (NLWRA) (Figure 3.5). A range of issues related to the availability, quantity and quality of Australian natural resources information were identified during the NLWRA and are presented in Australian Natural Resources Information 2002.

The processed data and results of the analyses carried out for the assessment have been brought together into a central database that is accessible through the webbased Australian Natural Resource Atlas (audit.ea.gov.au/ANRA/atlas_home.cfm). A data management infrastructure is proposed that will link the atlas with the State and Territory agencies' data archives thus enabling the NLWRA data and products to be more readily updated in the future. These links and this updating process may provide a suitable starting point for feeding Australian surface water and ground water data into global climate archives.

Australia, being an island and having no international rivers, does not currently distribute internationally any surface water or ground water data in either real time or near real time. Historical data are made available internationally upon request to the State and Territory water agencies.

Australia contributes data for 239 currently operating surface water stations to the Global Runoff Data Centre (GRDC) in Koblenz, Germany. These stations measure runoff from a mixture of small and large drainage areas and regulated and unregulated rivers. The data held by the GRDC for these stations are updated periodically.

Data for six river basins are made available for research purposes from the Asian Pacific Flow Regimes for International Experimental and Network Data (FRIEND) Water Archive (htc.moa.my/apfriend/wa). The basins are described in the UNESCO Catalogue of Rivers for Southeast Asia and the Pacific, Volumes 1, 2 and 3. Data for river basins included in future volumes of the catalogue will also be made available via this Water Archive.

Figure 3.5 Percent run-off from Australia's twelve drainage divisions, from the Australian Water Resources Assessment, 2000. (Courtesy National Land and Water Resources Audit).

Drought and water resources

Low rainfall conditions during the year resulted in 2002 being one of the driest years on record for Australia as a whole. Much of eastern Australia and southwestern Australia also experienced a dry year in 2001. In parts of southeastern Australia these two dry years have come on top of below average rainfalls over a prolonged period of about 6 years. The successive dry years have had a serious impact on water resources in eastern Australia with increasingly severe water restrictions being placed on the availability of irrigation supplies and urban water use. In Victoria during February 2003, many streams had dried up (Figure 3.6) and irrigation and/or water diversion bans were in place in 23 of the 28 river basins. Restrictions were in force in 268 towns, of which 20 were on severe levels of restriction, 90 on moderate levels and 158 on low levels.

For each urban water supply system, restrictions are applied in accordance with the Drought Response Plans developed by the relevant water authority. These Plans contain ‘rules’ or ‘triggers’ for the implementation of increasingly severe restrictions on water use, and other actions to further reduce demands or augment supplies. The triggers are typically linked to volumes of water in storage and/or streamflow levels, and they are set at levels that will ensure an adequate long-term reliability of supply. While there is potential for using seasonal forecasts to help develop restriction rules, as yet, most water managers take only qualitative account of seasonal forecasts in making operational decisions. This partly reflects the facts that the skill levels of seasonal forecasts for Victorian rainfall are not high for much of the year, and that the most useful forecasts for water managers would involve accurate predictions at the start of summer (i.e. November/December) of winter/spring rainfall (i.e. May/November) in the following year, which is beyond the scope of current seasonal forecasts for Australian rainfall.

Management of Water Resource Systems

The Bureau of Meteorology in collaboration with the Cooperative Research Centre for Catchment Hydrology (CRCCH) released the Climatic Atlas of Australia: Evapotranspiration during 2001. The atlas consists of average monthly and average annual maps of areal actual, areal potential and point potential evapotranspiration and is available as printed maps or gridded datasets on CD-ROM. Evapotranspiration is a large part of the water balance and in Australia almost 90 percent of the precipitation that falls is returned through evapotranspiration to the atmosphere. These maps and data satisfy a demand from the water industry for comprehensive evapotranspiration information for use in hydrological modelling for the development and management of water resource systems.

Figure 3.6 Map of streamflow status for Victoria, February 2003 (from Victorian Resources Online – www.nre.vic.gov.au/vro/water)

Australia’s climate variability imposes uncertainty in hydrologic systems that must be taken into account in the design and operation of water resource projects. In order to quantify this uncertainty, system simulation using stochastically generated data can be used. As part of its Climate Variability Program, CRCCH is undertaking a project to develop a national data bank of stochastic climate and streamflow models. This project will result in an agreed protocol for testing algorithms for stochastic generation of climate and streamflow data, algorithms for stochastically generating point daily rainfall and other climate variables for any location in Australia and a suite of computer programs that will enable practitioners to easily apply these algorithms. A second project under the CRCCH Climate Variability Program is modelling and forecasting hydroclimate variables in space and time. This project aims to reduce uncertainty due to the high variability of rainfall and streamflow by developing space-time models of rainfall and methods of forecasting rainfall and streamflow several hours to several months ahead. This project is expected to result in; computer software implementing a space- time rainfall model, a statistical method for forecasting seasonal streamflow, improved representation of surface hydrology in numerical weather prediction models and a suite of approaches for forecasting rainfall and streamflow several hours to several months ahead. The work for these projects is being undertaken within the Bureau of Meteorology and the University of Melbourne utilizing rainfall data from the Bureau of Meteorology NCC archive and streamflow data provided by the State and Territory water agencies.

A climate data set has been prepared for l0 locations in the Murrumbidgee River basin by the CRCCH. The data will be used as forcing data for land surface modelling experiments and the locations coincide with the sites in the CRCCH Murrumbidgee River Basin soil moisture monitoring program. The climate data prepared are 30- minute time series of rainfall, air temperature, specific humidity, wind speed, wind direction, incoming shortwave radiation and incoming longwave radiation. At present, the data have been compiled for the period from January 2000 to June 2002. The data will be updated every six months.

As a result of the prolonged period of below average rainfall in southeastern Australia, the 2002-03 summer period was characterised by widespread bushfires that affected an area of over 1.5 million hectares. In response to requests for information about the hydrologic impacts of the bushfires, the CRCCH has established a website (http://www.catchment.crc.org.au/bushfires) to deliver information useful to assist land and water managers with impact assessment and rehabilitation planning.

The Bureau of Meteorology has continued its support for a project to provide more reliable estimates of the probabilities of extreme rainfalls, including the Bureau’s Probable Maximum Precipitation (PMP) estimates. The methodology applied is based on joint probability analysis of the hydrometeorological factors contributing to extreme storm events. Monash University’s Department of Civil Engineering and the Department of Civil, Surveying and Environmental Engineering at the University of Newcastle are undertaking this project jointly.

The Bureau of Meteorology project to revise the Generalised Tropical Storm Method (GTSM) for estimating PMP was completed in early 2003. The project, which received significant financial sponsorship from major water authorities in Western Australia, New South Wales and Queensland, developed an improved generalized PMP method for application in regions of Australia affected by tropical storms. The project involved the development of a database of approximately 120 of the largest tropical storms in the rainfall record. These storms were analyzed to determine their site-specific components such as moisture availability and topographic influences in order to identify the most efficient storms over a range of areas and durations. Estimates of PMP made using GTSM will be an important component of future risk management studies of Australian dams.