Rivers and Floodplains
The rivers and floodplains of the south-west will be impacted by climate change mainly through a decline in rainfall (projected to be 30% by 2090), leading to a decrease in runoff. This, combined with a climate that is projected to have more intense rainfall events, means many of the region’s waterways, which have evolved to their current form today over millions of years, may be greatly modified. Streams that are spring-fed and/or dependent on groundwater will also be impacted by climate change through a lack of inflow from already reduced aquifers.
Most of the direct impacts of climate change on freshwater systems in southern Victoria are predicted to come from a decline in rainfall leading to a decrease in runoff. Modelling of the Southeast Coast drainage division (including the area covered by the five coastal CMAs in Victoria) found strong agreement across 15 climate models that runoff would decrease. With 1 °C of global warming, average annual rainfall is expected to decline by 0 to 9% and average annual runoff is expected to decline by 2 to 22 %. For 2 °C of global warming, the reductions in both rainfall and runoff are approximately double.
Some generic impacts of climate change of freshwater systems include:
- Increased frequency and severity of droughts
- Drier soil conditions
- Reduced stream flow
- Increased frequency and intensity of bushfires, resulting in greater sediment input to waterways
- Increased risks to freshwater and riparian ecosystems
- Increased water demand
The most vulnerable waterways to climate change are those in the far north west of the region and the Otway Ranges, especially those flowing southwards into the Southern Ocean. These waterways have small, confined catchments, are unregulated, rely on high levels of rainfall and are relatively short in length. Reduced runoff into these rivers and streams will have a detrimental impact on these systems. Those in the far north west are sensitive to the climate stressors such as reduction in March to November rainfall and an increase in November to April maximum temperature.
The vulnerability assessment (weblink) also shows that some rivers and streams will be more resilient to climate change. These include reaches of the Mt Emu Creek, Hopkins, Glenelg, Gellibrand, Leigh, Moorabool and Barwon rivers and this high resilience can be attributed to these specific reaches having greater adaptive capacity or being highly regulated flows and/or already highly degraded. As a result, there is limited scope for these reaches to be degraded further by climate change.
Existing approaches to riparian and waterway management can be adaptive if undertaken within the climate ready context. Management of non-climate threats through fencing, pest management and restoration can reduce the vulnerability of systems and build adaptive capacity. Existing restoration activities such as riparian revegetation, the removal of barriers and the creation of fish ladders, have a critical role to play in reducing the sensitivity of river systems through the enhancement of riparian ecosystem functions and services. Under climate change scenarios, the adaptive benefit of ongoing restoration and management can be enhanced if goals remain more ‘open-ended’ allowing for a range of future trajectories rather than focusing on meeting specific targets tied to antecedent reference conditions.
Protected areas will become increasingly important as they provide refugia, reduce the overall sensitivity and increase adaptive capacity across the landscape. Protecting existing and potential climate refugia and known resilient systems forms the backbone of biodiversity protection. Landscape level planning will be essential in building the adaptive capacity of systems through improved connectivity via corridors and bio links. Existing projects such as Habitat 141, The Yellow-bellied Glider Biolink Project and the Grampians to Pyrenees Biolink provide an opportunity to incorporate rivers and streams into protected area networks to benefit the ecological resilience of the entire region.