In the aftermath of natural hazards, opportunities often arise for society to make changes that prevent future losses. These changes can also have environmental impacts, increase preparedness, and contribute to sustainable development. Due to the loss of biodiversity and land degradation, there is an urgent need for actions promoting positive environmental changes. Reversing the trend of land degradation and biodiversity loss is motivated by various reasons, such as preserving ecosystem functions and services that offer protection against natural hazards and reducing drivers of climate change. However, due to land degradation, loss of ecosystems, and human settlements in hazard-prone areas, it is also necessary to take actions that reduce the risk of tsunamis by improving preparedness. Improved preparedness from a people-centered perspective is a crucial aspect of sustainable development.

The four papers that make up this thesis present and apply two new frameworks— one to assess the environmental effect of human-made societal changes, and one to evaluate the maintenance of a TEWS (Tsunami Early Warning System) over time. The two frameworks capture two aspects of change after a natural hazard: i) environmental impacts and ii) Disaster Risk Reduction (DRR). The thesis focuses particularly on time, a common aspect in both frameworks.

The results indicate that changes triggered by natural hazards have a dual nature in that their impact on the environment can be both positive and negative. The thesis also provides evidence that past natural hazards can create a delayed window, which can be used as an argument for nature conservation during the establishment of national parks.

The framework for evaluating the maintenance of a TEWS shows how difficult it is to operate all parts of the warning chain over time, from tsunami detection to evacuation. If parts of the chain are not maintained, the warning system may not be reliable.

Natural hazards can present opportunities for societal change. This thesis analyzes two types of changes: i) those with environmental impact and ii) those aimed at improving tsunami preparedness. It addresses a crucial gap in post-disaster literature by focusing on the environmental impacts of changes. In light of land exploitation and loss of biodiversity, it is critical to make changes that reverse these trends and support sustainable development. Unfortunately, not all natural hazards can be prevented. Tsunamis can severely threaten coastal communities, requiring preparedness and evacuation. A people-centered approach to preparedness is also an essential aspect of sustainable development.

The thesis includes four papers that present and apply two new frameworks—one to assess the environmental impact of societal changes and another to evaluate the maintenance of Tsunami Early Warning Systems (TEWS). The results reveal that changes, even if well-intentioned, made after natural hazards can have both positive and negative impacts on the environment. The TEWS maintenance framework also highlights the ongoing challenges in maintaining all warning system components.