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Lavaka (gullies) are often considered as the prime indication of a currently ongoing human-induced environmental crisis in Madagascar's highlands. Yet, lavaka are known to have existed long before human arrival and account for the majority of the long-term sediment input into the highland rivers and floodplains. The role of anthropogenic disturbances in their formation therefore remains highly debated and it is unclear whether lavaka erosion has recently increased. Here,we address these questions by evaluating the dynamics of lavaka in the Lake Alaotra region (central Madagascar). An overall birth to stabilization ratio of 6.1 indicates a rapid lavaka population growth over the period 1949–2010s. Using data on lavaka development we calculated a mean lavaka population age of 410 ± 40 years and estimate that the disequilibrium started at 870 ± 430 cal. BP. Floodplain sedimentation starts to increase around 1000 cal. BP and peaks over the last 400 years, thereby independently confirming this time frame of increased lavaka activity. Lavaka population dynamics modelling shows that a strong increase in environmental pressure over the last centuries is needed to attain current disequilibrium levels. A general drying of the climate since 950 cal. BP in combination with the introduction of cattle and growing human presence around 1000 cal. BP will likely have triggered the increase in lavaka erosion. However, the recent acceleration cannot be explained by climatic changes alone and seems to be linked to increased anthropogenic pressure on the environment. As such, we offer a fresh and quantitatively supported perspective on lavaka dynamics and human impact in central Madagascar, where our methodology can be used in other locations where similar questions on geomorphic equilibrium need to be answered. ispartof: Science Of The Total Environment vol:806 issue:Pt 2 ispartof: location:Netherlands status: Published online

Effective disaster risk reduction (DRR) presupposes awareness among key stakeholders on the causal factors that exacerbate disaster risks as well as a feeling of ownership over proposed DRR measures. Yet, the prevailing top-down communication of risk and the expert-centered knowledge have a limited impact in bringing significant positive change. Serious games respond to the need for a community-based DRR approach as they encourage a collective recognition of societal issues and co-learning at the different levels of the DRR governance system. However, there is still a gap in understanding how serious games facilitate co-creation of knowledge. In this article, we introduce DisCoord, a serious game first implemented in the landslide- and flood-prone Rwenzori mountains in South-West Uganda. Designed as a public pedagogy tool, Discoord bridges diverse views and sets of knowledge of DRR stakeholders separated by spatial and socio-cultural domains. Secondly, through a qualitative analysis of the dialogues, narratives and observation notes during the actual game sessions and debriefings, we explored the factors and processes that influence knowledge co-creation. Three different knowledge actors are involved in the co-creation process, namely the game designers, game facilitators and players. These actors have diverse pre-game views, which are expressed through the game rules, arguments, game strategies, and game outcomes, and are confronted within the public space provided by the game. We find that crises experienced during the game, real-life based arguments provided by the players and own interpretations by the players are key factors in the co-creation process. This study leads us to conclude that games like DisCoord are useful as a public pedagogy intervention as they bring different forms of knowledge together in a public space and facilitate co-learning. This paper also contends that countering a top-down approach of risk communication using a public pedagogy approach requires an openness towards the unpredictable, de-centered DRR, and plural co-learning outcomes.