Carsten Marohn

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.

A software coupling approach to assess low-cost soil conservation strategies for highland agriculture in Vietnam

Soil degradation is an environmental process mainly caused by land use decision-makers that has substantial feedback effects on livelihoods and the environment. To capture these feedback effects and the resulting human-environment interactions, we used an agent-based modeling approach to couple two software packages that simulate soil, water and plant dynamics (LUCIA), and farm decision-making (MP-MAS). We show that such a software coupling approach has advantages over hard-coded model integration as applied by most other comparable studies, as it facilitates combining of increasingly sophisticated individual models and can achieve a well-balanced representation of agricultural systems. Using a numerical application for a small mountainous watershed in northwest Vietnam we show the challenges in model coupling, calibration and partial validation, and explore the properties of the coupled model system. Scenario analysis covering the introduction of low-cost soil conservation techniques indicates that some of these techniques would have an impact on soil erosion, maize productivity and household income levels in the study catchment area under current conditions. However, maize yields and the adoption of soil conservation appear to be sensitive to the price of mineral fertilizers, with lower fertilizer prices impeding the adoption of soil conservation measures. The software coupling approach was able to capture interactions between decision-makers and natural resources, as well as the level of spatial variability, in more detail than the individual models. Still, the greater number of endogenous variables and thus degrees of freedom increased the importance of validation and testing parameter sensitivity of the results.

Crop production versus surface-water regulation: assessing tradeoffs for land-use scenarios in the Tat Hamlet Watershed, Vietnam

Local land uses play a critically important role in regulating hydrological services like surface-water runoff. This runoff influences the supply of water to streams and lowland agriculture. Land-use management decisions, in turn, are influenced by economic return. This article examines the tradeoffs between surface-water runoff regulation and income from crop production by using the land-use change impact assessment model and an economic analysis for a case study in Tat Hamlet Watershed, north Vietnam. The traditional composite swidden agriculture was used as baseline scenario, since it has been practised by farmers in the study area for decades. Two alternative scenarios were tested and compared with the composite swidden agriculture: expansion of maize monoculture and introduction of rubber plantations in the uplands. Among the land-use scenarios tested, rubber plantations appear to be better alternatives than maize monocropping in terms of surface-water regulation and improving economic return. However, implementation should consider the interests of local stakeholders as well as an analysis of possible risks and uncertainties involved.

Integrated Modeling of Agricultural Systems in Mountainous Areas

People’s decisions with respect to agricultural land use and management practices have had a major impact on natural resource degradation in Vietnam and Thailand for centuries. In addition to an ever-increasing population density, economic transformation and market integration have exacerbated the pressure on natural resources in the rural areas of both countries, particularly during recent decades. From its beginning, the Uplands Program has sought to address research questions related to the impacts of land use management on natural resource degradation at the landscape level in Southeast Asian countries, as have researchers linked to the Program in the area. Integrated modeling of land cover and land use change, as a means to simulate effects which extend over various spatial and temporal scales or scientific domains, began to play a more prominent role within the Uplands Program after 2006. This chapter highlights modeling approaches and decision support tools used as part of the Uplands Program to investigate various research questions at the human–biophysical interface, and will compare modeling approaches, looking at the issues of land use and management impacts from different angles, whereby the different focuses used by each model have resulted in different levels of detail and precision in various respects.