Residual impact projection

Residual impact projection includes adaptation of actors in projecting impacts. Residual impact projection methods analyse the possible impact of climate change and other potential drivers on a system at risk, after considering to what extent adaptation can reduce the projected impacts.

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Residual impact projection includes adaptation of actors in projecting impacts. Impact projection methods analyse the possible impact of climate change and other potential drivers on a study unit. The fundamental theoretical assumption of impact analysis is that it is possible to analytically distinguish between a study unit and its (natural and socio-institutional) environment in the sense that the environment influences the study unit but whatever happens "inside" the study unit does not feed back on its environment. This separation allows for the representation of the evolution of the environment in form of a set of scenarios that are independent from the model used to represent the study unit. If changes in the study unit would influence the environment, than an integrated (assessment) model would need to be used for representing both the study unit and its environment together. We follow the IPCC in distinguishing methods that analyse potential impacts, which are those that "may occur without considering adaptation" (Parry et al. 2007: 876), in opposition to methods that assess residual impacts, which include adaptation. One problematic aspect about potential impact assessments is that the theoretical assumption made that people don't adapt is often empirically rather unlikely to be met. The potential impact that "many millions more people are projected to be flooded every year due to sea-level rise by the 2080s", reported in the AR4 WG2-SPM (IPCC 2007), for example, is rather unrealistic because this would assume that people continue to live in the coastal zone even though they experience frequent flooding or even permanent inundation (Hinkel 2011b).

Question addressed

What are the impacts of climate change ?

Conditions of applicability

Interaction between the drivers and the study unit can be formally represented as a computational model.

Theoretical assumptions

People affected adapt. Adaptation can be formally represented by a computational model.

Steps taken

1. Selection of climate and socio-economic scenarios 2. Selection of adaptation options and strategies 3. Computation of the impacts of the scenarios and the adaptation strategies 4. Evaluation of impacts using impact indicators

Results achieved

A list of propositions that map each scenario to a residual impact. Each proposition is interpreted: 'When the world evolves according to scenario e and one adapts according to strategy a, the impact on the vulnerable system will be i.'

Issues involved

How to model adaptation? Model of adaptation (e.g. dumb, typical, smart and clairvoyant farmer) used has a significant indication on the results produced.

Example cases from literature

Hinkel et al. (2010) address the question of what will be both the potential and the residual impacts of sea-level rise on coastal countries of the EU27. The authors use the DIVA model to project the impacts of various sea-level rise and socio-economic scenarios on the countries first without any adaptation (potential impacts) and than with an adaptation strategy (residual impacts) that raises dikes to protect against coastal flooding and nourishes beach to protect against coastal erosion. It is found that the while the potential impacts are substantial, adaptation reduces these impacts significantly by one or two orders of magnitude.


Read more in the Toolbox under the following category:

Modelling future impacts

This section is based on the UNEP PROVIA guidance document

Criteria checklist

1. You want to appraise adaptation options.
2. The focus is either on collective actions and there are no conflicting interests of private actors, or the focus is on individual collective actions.
3. Decisions can be formalised.
4. The set of options does not only include short term ones.
5. Residual impacts can be projected.