Shifts in Environmental Targets for Managing Fine Sediment in Rivers Are Anticipated Under Climate Change.

Targets for attribute states indicating freshwater ecosystem health are often set to help manage local activities without accounting for climate driven impacts, despite climate being a known driver of the attribute. A key challenge is anticipating how environmental attributes and corresponding target attribute states will respond to climate change alongside impacts of local anthropogenic activities. We present a method to predict climate-driven shifts in target attribute states for suspended and deposited fine sediment, as specified in existing environmental policy for Aotearoa-New Zealand. The policy uses a river environment classification derived from climate, topography, and geology inputs to determine spatially-distributed target attribute states. We calculated and mapped class membership of the classification and resulting target attribute states for future climate scenarios from regional projections. Apparent spatial patterns in shifts to warmer and drier climate classes are anticipated for a considerable proportion of river segments under the highest future emissions scenario towards the end of century. Climate-driven shifts in class membership led to shifted target attribute states corresponding to either increased or decreased sediment targets depending on location, and the emergence of conditions that have no specified environmental targets because they fall outside of existing classes. Findings highlight the potential impact of climate change upon both target attribute states and actual fine sediment states which should be considered when devising environmental classifications and setting target attribute states. Our method offers a practical approach to anticipate climate-driven impacts on any environmentally-driven spatial classification used to derive management units and target attribute states.