The rivers and streams of the region will be impacted by climate change mainly through a decline in rainfall (projected to be 30% by 2090), leading to a decrease in runoff. Combined with a climate that is projected to have more intense rainfall events, this means many of the region’s waterways that have evolved to their current form over millions of years may be greatly modified. More intense rainfall events may lead to more waterways being susceptible to bank erosion. 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.
The most vulnerable waterways in the region are those in 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. One adaptive approach that was suggested during one of the Regional Expert Panel Workshops is to allow the forest in the watershed of these catchments to grow old under a regime of minimal disturbance as this may increase catchment water yield.
Many tributaries of the upper catchments to the north of the region will also be highly vulnerable to climate change. This is largely attributed to reduced runoff as well as high levels of modifications that have been made to these systems since European settlement, usually in the form of reservoirs, weirs and similar infrastructure. Rethinking how this infrastructure can be managed may lead to rivers and streams becoming more resilient to what will be a warmer climate with less rainfall.
The vulnerability assessment also shows that some rivers and streams will be more resilient to climate change. These include reaches of the Gellibrand, Leigh, Moorabool and Barwon rivers and this high resilience can be attributed to these specific reaches 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, mainly due to their already reduced flows.