Understanding multiple thresholds of coupled social-ecological systems exposed to natural hazards as external shocks

Societies and ecosystems worldwide are increasingly subjected to hazards of natural and anthropogenic origins. Increasing the resilience and reducing the vulnerability of social–ecological systems (SES) so that they can withstand these shocks is crucial. External shocks (e.g. cyclones, earthquakes, tsunamis, floods) can induce an SES to move from one regime to another (or one stability domain to another), the latter typically being unfavourable. This can be through the disruption of ecosystems and the services they provide to society and/or through disruption of the social and economic structure and networks of the SES. Important characteristics of SES are the thresholds (boundaries) separating stability domains, but these are very difficult to evaluate because of the complex nature of SES. We use the example of the 2004 Indian Ocean tsunami impact on groundwater resources and the coastal communities relying on them in Sri Lanka, to illustrate that a practical approach for SES threshold characterisation could be through description of the dependency of social groups with respect to essential ecosystem services and through an understanding of the state of the ecosystems providing these services. However, this is not sufficient and changes of adaptive capacities of different social groups, access to the environmental services and the interventions undertaken by different actors also need to be considered. Furthermore, the question of when (time and phase) and why (stimuli) SES might shift into another state should be reviewed more critically. The implication is that multiple thresholds within the sub-components of the SES have to be assessed