PRAFOR: Probabilistic drought Risk Analysis for FORested landscapes

Lead Research Organisation: UK CENTRE FOR ECOLOGY & HYDROLOGY
Department Name: Atmospheric Chemistry and Effects


This research aims to extend theory for probabilistic risk analysis of continuous systems, test its use against forest data, use process models to predict future risks, and develop decision-support tools.

Risk is commonly defined as the expectation value for loss. Most risk theory is developed for discrete hazards such as accidents, disasters and other forms of sudden system failure. Less theory has been developed for systems where the hazard variable is always present and continuously varying, with matching continuous system response. We can think of dynamic systems whose performance varies with ever-changing resource availability or other dynamic constraints, e.g. crop growth depending on water supply, or urban health as a function of air pollutant concentration. Risks from such continuous hazards (levels of water, pollutants) are not associated with sudden discrete events, but with extended periods of time during which the hazard variable exceeds a threshold. To manage such risks, we need to know whether we should aim to reduce the probability of hazard threshold exceedance or the vulnerability of the system. In earlier work (Van Oijen et al. 2013,, we showed that there is only one possible definition of vulnerability that allows formal decomposition of risk as the product of hazard probability and system vulnerability (R = p[H] V). We have used this approach to analyse risks from summer droughts to the productivity of vegetation across Europe under current and future climatic conditions (Van Oijen et al. 2014, 2014.html). This showed that climate change will likely lead to greatest drought risks in southern Europe, primarily because of increased hazard probability rather than significant changes in vulnerability. We plan to improve on this preliminary theoretical work in different ways:

- Add one more major risk component to the analysis: exposure to the hazard, so that risk becomes the product of three terms. That will allow distinguishing between hazards that only affect few individuals or points in space to those that affect larger populations and areas.
- Derive equations for quantifying the uncertainties in our estimates for risk and its components. Only with quantified uncertainties can the estimates play a legitimate role in decision-support.
- Relax assumptions underlying previous work and develop the theory for any type of joint probability distribution for hazard, exposure and vulnerability. This will likely require the use of extreme value theory and numerical estimation using Bayesian hierarchical modelling.
- Test our equations and numerical algorithms on both observed and simulated data in this research. Observational data will be from forests in the U.K., Spain and Finland. Simulated data will be generated by process-based modelling of forest response to climate change.
- Analyse the underlying causes of vulnerability, as represented by the parameters and processes of the process-based forest model.
- Show the wider implications of the risk decomposition and the uncertainty quantification, by embedding the equations in Bayesian decision theory to allow identification of optimal drought management measures.
- Develop an interactive web application as a tool for preliminary exploration of risk and its components to support decision-making.

The work will be carried out by CEH-Edinburgh in close collaboration with Biomathematics and Statistics Scotland (BioSS, part of the James Hutton Institute, Aberdeen) and Forest Research UK (Alice Holt, Aberdeen, Edinburgh). Data and expertise from Spain and Finland will be provided by two Project Partners: the University of Alcalá (Madrid, Spain) and the Natural Resources Institute (Luke-Helsinki, Finland).

Planned Impact

Our risk analyses will inform future national climate change risk assessments (CCRA), and future IPCC reports. The project outcomes will benefit a variety of stakeholders whom we are in contact with:

- The Forestry Commission (England), Natural Resources Wales, Scottish Forestry and NI Forest Service in the evolved administrations through evidence on future climate suitability, forest adaptation measures and conservation strategies for two major conifer species.
- DEFRA, Natural England and Scottish Natural Heritage and other agencies through evidence on likely changes in risk and impacts on forest ecosystem structure and function.
- Public and private sector forestry practitioners, producers and processors (via UK Forestry Societies, Institute of Chartered Foresters and Confederation of Forest Industries through the DSS developed and through the exploration of the potential of management options to reduce risk. Our work will also provide valuable evidence to specialist woodland groups e.g. the Native Woodland Discussion Group, Woodland Trust, RSPB.
- European groups seeking evidence for policy-making and national and EU long-term forest management planning such as European Forest Institute, European State Forest Association and national Forest Owners Associations through the Confederation of European Forest Owners.
- This research will also be of substantial interest to the broad swath of the public concerned about the sustainability of our way of life, woodland resource, woodland resilience and their links to climate security.
- Development of this new risk assessment framework will have many possible applications across environmental science, in addition to the immediate examples developed in this proposal. In forestry, it will help develop further FR's work on wind risk (UK forestry's biggest present risk to production) and in risks to tree health from various pest and pathogens, where there is considerable concern. The improved assessment of current and future drought risk will be particularly useful. The combined risk assessment and modelling framework will lend itself to application to other novel species to help define 'climate-smart' forestry, and strengthen sector resilience through species diversification. At the European scale, the methodologies developed will allow extensive assessment of Scots pine vulnerability.


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Title Probabilistic Risk Analysis and Bayesian Decision Theory 
Description The theory developed in PRAFOR has has been published in a a book "Probabilistic Risk Analysis and Bayesian Decision Theory" The theory in PRAFOR extends the previous theory on risk, defined as the statistical expectation of loss, that can be formally decomposed as the product of two terms: hazard probability and system vulnerability. This required a specific definition of vulnerability that replaces the many fuzzy definitions abounding in the literature. In PRAFOR the approach as been expanded to a more complex risk analysis with three components, now including exposure, rather than two, and with various definitions of hazard. New equations have been derived to quantify the uncertainty of each risk component and to show how the approach relates to Bayesian decision theory. The theory developed in PRAFOR and presented in the book provides precise definitions, new theory, and many examples with full computer code in the language R. The approach is based on straightforward use of probability theory which brings rigour and clarity. 
Type Of Material Improvements to research infrastructure 
Year Produced 2022 
Provided To Others? Yes  
Impact This theory does not directly impact on animal welfare 
Title Bayesian Decision Theory for Drought Risk Analysis in Forested Catchments 
Description We have now derived a decision theory modelling approach to use in conjunction with the risk analysis tool produced last year. There are two versions, one which uses approximations to the fully Bayesian model, and an alternative which makes fewer assumptions and uses Markov Chain Monte Carlo methods. This has involved a novel comparison of decision theory and risk analysis with clear identification of which approach is appropriate in which context. The models have been completed in R and using the "Nimble" package for simulation, to allow full integration with forest models and weather generators or emulators. The approach has been described in a draft book which will be published in due course by Springer Nature. A Github repository containing code will also be made available at the conclusion of the project, now delayed (with approval) to May 2022. 
Type Of Material Data analysis technique 
Year Produced 2022 
Provided To Others? No  
Impact We are at present creating usable case studies using actual drought and forestry data, in co-operation with Forest Research in the UK and with the University of Alcala in Spain. 
Description Presentation to European Forest Institute (EFI) funded project FOSPREF-Wind 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation to an end-of-project webinar for the EFI funded project FOSPREF-Wind. The talk demonstrated some of the work in PRAFOR on model development and risk theory.
Year(s) Of Engagement Activity 2022