Laxman Joshi

Influence of coastal vegetation on the 2004 tsunami wave impact in west Aceh

In a tsunami event human casualties and infrastructure damage are determined predominantly by seaquake intensity and offshore properties. On land, wave energy is attenuated by gravitation (elevation) and friction (land cover). Tree belts have been promoted as “bioshields” against wave impact. However, given the lack of quantitative evidence of their performance in such extreme events, tree belts have been criticized for creating a false sense of security. This study used 180 transects perpendicular to over 100 km on the west coast of Aceh, Indonesia to analyze the influence of coastal vegetation, particularly cultivated trees, on the impact of the 2004 tsunami. Satellite imagery; land cover maps; land use characteristics; stem diameter, height, and planting density; and a literature review were used to develop a land cover roughness coefficient accounting for the resistance offered by different land uses to the wave advance. Applying a spatial generalized linear mixed model, we found that while distance to coast was the dominant determinant of impact (casualties and infrastructure damage), the existing coastal vegetation in front of settlements also significantly reduced casualties by an average of 5%. In contrast, dense vegetation behind villages endangered human lives and increased structural damage. Debris carried by the backwash may have contributed to these dissimilar effects of land cover. For sustainable and effective coastal risk management, location of settlements is essential, while the protective potential of coastal vegetation, as determined by its spatial arrangement, should be regarded as an important livelihood provider rather than just as a bioshield.

Users’ perspectives on validity of a simulation model for natural resource management

Managers of agro-ecosystems trade off food production and livelihood strategies against environmental services. They need tools to prospect a wide range of external conditions. Integrated simulation models allow stakeholders to discuss the plausible behaviour of agro-ecosystems and to evaluate dynamic trade-offs, as a basis for planning and policy making in agriculture and natural resource management. However, simulation models need to gain stakeholders’ acceptance before they will be utilized. Gaining stakeholders’ acceptance likely requires salience, credibility and legitimacy. We surveyed the perceptions and expectations of 122 potential model users in four countries, prioritizing these model attributes. A possible shift in user perception was assessed during a participatory model evaluation of a resource management model (FALLOW) for post-tsunami development in West Aceh (Indonesia). Potential model users, comprising natural resource managers, policy makers, lecturers and scientists, ranked salience as the most important characteristic for an integrated simulation model, followed by credibility and legitimacy. Model users’ occupation, prior exposure and interest in using a simulation model did not have a statistically significant influence on users’ perceptions of model attributes.