Assessing the Impact of Climate Change on Environmental Outcomes in the Context of Natural Climate Variability

Abstract

Climate change has emerged as a key threat to river ecosystems. This study presents a generic, conceptual framework for assessing the significance of climate change impact for ecological outcomes. Within the framework, multiple sequences of streamflows with a length that is “critical” to target species are derived under current and future climates; ecological responses are assessed using models that consider the influence of flow sequencing; the ranges of ecological responses under future and current climates are compared to indicate the significance of impact. This framework allows the degree of future climate risks to ecosystems to be assessed with reference to the range of behavior under current conditions. An example application of the approach to the Yarra River, Australia, show that careful use of environmental water rights could provide a similar range of outcomes under future and current climate, where the range of outcomes due to natural variability are appreciably greater than the shifts induced by climate change. This study demonstrates the importance of incorporating natural variability in impact assessments and shows the flexibility of active water management.