Water is essential for all forms of life- not just human, but for the survival of our natural ecosystems, communities and productive economies. Australia, as the driest inhabited continent on earth, is well accustomed to a climate of extremes best characterised by its history of alternating floods and droughts. Historically, Australia has experienced several prolonged droughts such as the Federation drought (1895-1903), the World War II drought (1939- 1945), and the Millennium drought (1997-2009). These have often been punctuated by extreme flood events which mark the other key challenge in managing water resources in Australia.
“Water and its availability and quality, will be the main pressures on, and issues for, societies and the environment under climate change.” (IPCC, 2007).
Listen to some of the world’s leaders in water resource planning discuss the key challenges of water security planning as a global “tipping point”.
The climate events of most concern to water planners and managers are those that reduce the availability and reliability of water supplies, including the occurrence of prolonged dry periods (droughts). For many industries the important climate variables are rainfall, temperature and evaporation, and their variability on daily, monthly, seasonal and annual timescales. These are key variables in the hydrological cycle.
The climate system and the hydrological cycle are strongly connected and understanding the interactions between these two systems is important, since variations in climate can trigger extensive changes in the hydrological cycle.
Within a simple water balance model, the volume of water available as surface water and ground water resources are the excess of precipitation over evapotranspiration.
The aridity index for example, denotes the amount of water available over the year at a given location. It is defined by the ratio of the annual potential evapotranspiration(potential moisture loss) and precipitation (moisture supply).
Point and click to the colour boxes to understand potential implications of different future climates on hydrological cycle and interactions with vegetation.
Climatic factors have a direct effect on evapotranspiration through changes in potential evaporation that occur with changes in solar radiation, humidity, temperature and wind speed. All these factors are likely to be influenced by climate change.
Vegetation cover also influences evapotranspiration, with deep rooted trees and perennial species generally returning more water to the atmosphere than annual grasses and other shallow (Zhang et al., 2002). Higher levels of carbon dioxide can result in greater levels of water use efficiency by plants, resulting in reduced transpiration. At the same time, associated climatic effects such as higher temperatures, changes in rainfall and soil moisture could either enhance or negate potentially beneficial effects of higher carbon dioxide concentrations on plant physiology.
Recent work across Australia highlights the complex interactions between carbon-dioxide and water availability.
Projecting future regional precipitation is still a challenge for climate science and, to date, it is not clear whether future climate will be drier or wetter, especially during the summer season.
The video below shows annual precipitation anomalies (change relative to historical reference period 1986-2005) simulated by 11 downscaled models. The animation shows large spatial and temporal variability.
However, models do agree that winter (June to August) and dry-season (May to October) rainfall are expected to decrease in future as illustrated in the video below.
While rainfall is the most important driver of surface water, potential evapotranspiration also plays a major role determining aridity regimes and water availability.
The maps below show how climate regimes and surface water availability may change across Queensland’s river basins based on climate models simulations. The results are based on the multi-model average for Aridity Index and Streamflow changes.
Climate models suggest that in 2030 most of Queensland’s River basins may already experience reductions on surface water availability. Burdekin, Fitzroy and Burnett River basins may present a 10% reduction on streamflow.
With increasing aridity, some South East Queensland catchments may shift their climate regimes from Wet to Semi-arid by 2050. This poses a risk to water security as streamflow is expected to decrease up to 20%.
In 2070 western basins may present some increase in streamflow, due to rainfall changes. However, we still do not know whether these changes will be distributed over the year or concentrated on extreme storms.
In 2090 extremely arid basins may cover a significative part of the state and a consistent reduction on water availability is expected all over the coast. Gulf of Carpentaria basins may experience up to 50% reduction on streamflow.
The time-series simulation below highlights expected changes in Queensland’s water availability as measured by aridity index and expected streamflow changes based on aridity and rainfall changes.
Point and click to a local government area in the map below and check the plots to understand how do climate models project future aridity and streamflow across Queensland’s regions.
The timeseries for aridity index shows a clear increase into the future. However, changes in precipitation or streamflow over time are less distinct. This is primarily because of the interdependencies among the climate factors, and as such the hydrological responses of climate change are often highly non-linear.
Seasonal hydrological responses are notably dependent on regional water and energy availability, and are affected by seasonal conditions of soil moisture and in some cases snow cover. As such, accurately predicting future water availability at both the global and regional scale is possibly the most challenging.
Several industries now incorporate climate risk into water security planning for their sector and there is growing awareness of the need to do so. For example, in south-east Queensland, Seqwater the region’s main water supply authority, has produced its second Water Security Program Plan (2016-2046) which focuses on ways to ensure the delivery of safe, cost-effective water and catchment services to communities across South East Queensland.
The National Water Initiative (NWI) Policy Guidelines through their Risk Assessment Module (2010) also provides guidance on developing a risk-informed approach to water planning and management, and climate risks can be considered within this approach.
Climate risks within a water planning period are also informed by rainfall and runoff information services. For example, the Bureau of Meteorology provides information such as biennial Australian Water Resources Assessments, seasonal streamflow forecasts and updates to the state of the El Niño Southern Oscillation and Indian Ocean Dipole. These tools can be used to understand when dry sequences are likely to emerge, allowing water planners to respond. There is also continuing research into identifying characteristics of the global climate system that are relevant to developing future climate and runoff projections for the region.
The use of historical rainfall and runoff records is also used to help communicate the risks associated with climate variability. However, recent research using ice-cores from Antarctica, for example, highlights concerns with only using the historical records as they do not represent the full range of variability. Significantly longer and more frequent wet and dry periods were experienced in the pre-instrumental period (that is, before the 20th century) compared with the period over which records have been kept.
The palaeoclimate proxy records such as those obtained from ice-cores, palaeoflood, long-term river discharge and tree-ring records can be additional source of data on the longer time-scales (>100 years) to better inform planning and risk management of water resources.
The Queensland Future Climate dashboard provides state-of-the art data on key climate variables that can now be incorporated into assessing climate risk in water security planning. However, like all model outputs, there is no one-size-fits all approach and industries are encouraged to use the data to test scenarios relevant to their sector.