Assessing and managing risks to environmental water outcomes in a changing climate

In many river basins, environmental water is used to mitigate the impact of anthropogenic change on freshwater ecosystems, such as water abstractions or river regulation. However, climate change presents significant threats to freshwater ecosystems worldwide, and jeopardises investments in environmental water management. Existing environmental water regimes tend to assume climatic stationarity and pursue flow recommendations based on long-term historic flow statistics. Changes in the hydrological cycle can reduce water availability, increase the likelihood of damaging floods and droughts, or increase competition for freshwater ecosystems through the proliferation of invasive species. These changes also make it more difficult to achieve river management objectives derived from historic flow regimes and water availability with environmental water. A better understanding of the impact of climate change on environmental water outcomes, and how flow regimes can be adapted, is needed to promote sustainable river management. Adapting to climate change requires both predicting the ecological consequences of changes in hydroclimatic conditions and assessing the effectiveness of intervention and adaptation options available to river managers. These tasks are hampered by large uncertainties in how the climate may change and how ecohydrological factors will respond. River managers need methods and tools that accommodate this uncertainty and help them to make decisions that are robust under differing climate futures. The primary objective of this thesis is to assist in understanding and managing the impacts of climate change on environmental water outcomes. Four research questions were identified toward this objective: Which combinations of hydrological and ecological modelling methods provide the most useful outputs for understanding risks for freshwater ecosystems in the context of uncertain climate change? How can water resource models be improved to allow the consideration o