Modelling of lake level under climate change conditions: Lake Purrumbete in southeastern Australia

Lake Purrumbete is located in western Victoria, Australia, and is highly regarded for its ecological, social, economic and scientific values. Recently, many lakes in the region have been dry or at their lowest level in recorded history, due to a drought that broke in 2010. For this study, a modified difference water budget method was employed to estimate net groundwater flux through the difference between the level of the lake and the water table, along with the specific yield and area of the aquifer. This model successfully modelled the lake level fluctuations. In recent years, Lake Purrumbete has fallen below the outflow level; however, because of its large volume, changes in salinity to date are minor and do not affect its freshwater status. An understanding of how these systems will behave in the future and how they may be best managed in a drying climate is considered an important step to adapt to climate change. Postulated future climatic changes in the region of the lake were used to project the lake level fluctuations to 2030 using the water budget model, and showed that dry conditions would cause the lake level to remain below its outlet elevation, but wet conditions would result in a significant recovery in the lake level. If the level of Lake Purrumbete continues to fall, the main threat to its ecological status will be the potential loss of some significant areas of fringing wetland habitat. The lowering in lake level could cause a shift in the abundance of algal plankton and so influence the whole lake food web. This may reduce the invertebrate diversity of the lake.