Climate change uncertainty and natural flow regime variability – implications for environmental flow protection in England

Sustainable development in the Anthropocene is jeopardised by a multitude of existing and emerging pressures on freshwater ecosystems. The protection of environmental flows represents a key strategy for balancing anthropogenic water demand with the requirements of healthy freshwater habitats. Using England as a case study, this thesis examines three dimensions of water management pertaining to environmental flow protection. The first dimension is the variability of natural flow regimes and its representation in large-scale environmental flow guidance. A new hydrological framework for classifying natural and modified regimes was developed that distinguishes five river types. Their natural regimes vary most strongly in the magnitude of low, average and high flows, the frequency of high flows, the duration of flow events and the timing of average and high flow events. These hydrological indicators are suggested as new country-scale protection targets and this framework provides decision makers aiming to restore flow regimes and/or develop protection strategies for modified regimes with natural reference conditions. The second dimension relates to the high climate change uncertainty and its implication for streamflow projections. Two catchments from different regime classes served as case studies for a detailed analysis of climate change impacts on streamflow elements relevant for environmental flow management. Sampling different types of climate model uncertainty across a range of emissions pathways, vastly different streamflow responses are projected. The hydrological response under climate projections sampling climate model parameter settings is substantially stronger and drier than under projections sampling climate model structure. These hydrological projections can guide climate change adaptation, in particular improved abstraction management, in these case study catchments and in similar catchments more widely. The third dimension relates to policy, governance and social environment of water management. Combining a simple water balance model and stakeholder consultation, environmental flow allocation scenarios were evaluated and the shortcomings of current water management and governance in addressing existing and emerging pressures were identified. Five strategies were outlined for closing adaptation gaps and enhancing water management in a way that improves environmental outcomes and the balance with human water use under climate change. This thesis informs and contributes to enhanced environmental flow protection and therefore freshwater resilience and sustainable development in the Anthropocene.