Joining the dots: integrating climate and hydrological projections with freshwater ecosystem values to develop adaptation options for conserving freshwater biodiversity

Adaptation Research Grants Program
Leon Barmuta
University of Tasmania

Executive summary from final report:

Much climate modelling available in Australia is spatially too coarse to be useful for adaptation planning for freshwater biodiversity. Downscaling of global climate change models will become more common and will be essential for finer-scale planning and management of adaptation responses to climate change. As this happens, states and territories around Australia have several resources available to assist in planning adaptations to conserve freshwater biodiversity: data on climate change, rainfall-runoff models to predict how water moves through the landscape, and various data bases recording the occurrence of freshwater plants, animals and other ecosystem values. These resources vary in their spatial resolution and completeness, and the data sets and models have often been developed in isolation. 

These, then, are the ‘dots’ that need to be joined up so that we can understand how different climate futures will impact our freshwater biodiversity. Tasmania is uniquely placed to do this joining up because it is the first state to have the combination of finely resolved, downscaled climate models (from Climate Futures Tasmania), hydrological models—to convert runoff data into flows in rivers and inflows into wetlands—and a comprehensive planning tool for aquatic ecosystems (CFEV: Conservation of Freshwater Ecosystem Values) which maps biodiversity assets and ecosystem values consistently across the state. These resources, combined with the existing, healthy networks between researchers, managers and stakeholders enabled Tasmania to provide a test case for the integration of risk assessment and management actions at catchment and regional scales. 

The aim of this research was to investigate and test the steps necessary in developing a planning framework for adaptation options to conserve freshwater biodiversity in the face of climate change. We used Tasmania as a test case to demonstrate how downscaled climate model outputs could be integrated with spatially resolved hydrological models and freshwater biodiversity data. This enabled us to scope adaptation actions at local, regional and state scales for Tasmania, and to explore how priorities might be set, and what implications this process had for policy.

Of the six downscaled climate models available, we used the driest, the wettest and a model closest to the ‘average’ of the six models. We did this because we wanted to explore how uncertainties in the modelling process affected prioritisation and policy development. Water temperature variables were computed from projected air temperatures across the state. Hydrological modelling was straightforward in those areas of Tasmania for which rainfall-runoff models were well-developed for natural catchments, and a number of hydrological variables relevant to different biodiversity assets was selected. The changes relative to the reference period (1961–1990) in these variables was computed for each model for different time periods into the future, with most of the focus on 2010–2039. Data from the literature and expert opinion was then used, via Bayesian Belief Networks, to link probabilistically the sizes of these changes (hazards) to their consequences on each biodiversity asset to provide a probability-based assessment of the risk to that asset for the given time period. These risks were then mapped for each river segment and wetland for each climate change model. 

We concluded that downscaled climate modelling, linked with modelling of catchment and hydrological processes, refines projections for climate-driven risks to aquatic environments. Spatial and temporal hazards and risks can now be compared at a variety of scales, as well as comparisons between biodiversity assets (e.g. relative risk to riparian vegetation v. in-stream biota). Uncertainties can be identified and built into adaptation processes. Notwithstanding this progress, we identified a number of issues that need to be addressed in order to increase confidence in this process.

The main issues for improved and timely modelling are: frameworks for using and downscaling outputs from improved global climate models as they become available; better data on thermal tolerances of freshwater biota; and improved methods for predicting key water temperature variables from air temperature and other biophysical predictors. Improvements are also needed in updating and maintaining high quality biodiversity data sets, and better spatially explicit information on the contributions of groundwater to surface waters and rates of recharge. 

The list of adaptation options available to planners is extensive, but workshops and consultations showed that the key challenge is to organise these options so that stakeholders are not overwhelmed.  Scenario modelling that incorporates explicit tools for comparing costs, benefits, feasibility and social acceptability should help with setting priorities but require further development. 

A review of current Australian policies revealed a variety of responses driven by both water reform and climate change agendas. Many agencies are actively revising their policies to accommodate adaptation. However, we note that much of the reform of the water sector in the last 10–15 years has aimed to improve certainty for non-environmental water uses. Under the National Water Initiative, governments have agreed that entitlement holders should bear the risks of reduced volumes or reliability of their water allocations as a result of changes in climate. The key opportunity for uptake of human adaptions to climate change is by developing and periodically reviewing water management planning tools. Flexibility in the planning process will be crucial, especially given the divergent projections yielded by different climate models in some regions. 

Pathways need to be developed for integrating the traditional evolution of planning and policy with the needs for climate change adaptation in aquatic ecosystems. Formal mechanisms for the uptake of knowledge about identified risks into policy and legislative instruments remain under-developed in most jurisdictions, although there is considerable activity and continuing negotiations within this space. An even bigger challenge is to integrate multiple adaptation strategies (sometimes at different scales) to achieve specific adaptation objectives within regions or catchments—especially where a mix of water management and terrestrial management is required.