|Student:||Bastian van den Bout|
|Timeline:||March 2016 - 17 June 2020|
The behavior of hazardous land surface processes is substantially influenced by their repeated or simultaneous occurrence. Hazardous land surface processes include erosion, flooding, flash floods and debris flows, which frequently occur in tropical semi-mountainous regions. The hydrological cycle often triggers hazardous land surface processes by intense precipitation events. As precipitation is a trigger that applies to a variety of hazardous land surface processes, this results in multi-hazard events where several processes are triggered simultaneously. Multi-hazard events have complex internal interactions and that have substantial impact on their behavior, and change the way that the land surface is altered (Figure 1).
Figure 1 The cascading effect of hazardous land surface processes through the altered land surface state.
The substantial influence of multi-hazard interactions and temporal feedbacks on the behavior of hazardous land surface processes has been reported in a variety of environments. Spatial interactions include blocked rivers or drainage channels by debris flows, in turn causing flooding. Flow properties can be directly affected, such as the viscosity of debris flows when they are diluted by overland flow. Several temporal feedbacks are furthermore known. Debris flows frequently leave loose materials exposed to runoff, where vegetation only restores after several decades. In many areas prone to flooding, storms cause debris and sediment deposits in channels and rivers, which decrease transport capacity.
Important fields where a complete understanding of the development of hazard behavior is required are long term Disaster Risk Management (DRM) and Urban Planning. Disaster risk can be defined as the combined expression of vulnerability, exposure and hazard (Figure 2). The cascading effects of multi-hazard events strongly influences the hazard behavior. Simultaneous or repeated occurrence of land surface processes alter the process behavior and therefore hazard, exposure and risk. Vulnerability is furthermore influenced through time by the reduced effectiveness of disaster risk measures. DRM can, through understanding and through adaptation and mitigation, reduce the financial damage and casualties that are caused predominantly by land surface hazards. The decision making process for both the adaptation to, and mitigation of, extreme land surface processes is predominantly based on future projections of risk, exposure and vulnerability. Long-term DRM plans are generally constructed for the coming decades and therefore need a long term vision on the impact of extreme land surface processes. Due to this, an increase in understanding of cascading feedbacks in multi-hazard behavior would significantly aid the decision making process for DRM.
Within the research project, two primary goals are set. First, a modelling method is developed that includes both geomorphological processes such as debris flows, (shallow) landslides and erosion, and hydrological processes, such as infiltration, interception, runoff and flooding (Figure 2). Within this model, that is primarily based on existing knowledge, the interactions between different hazardous processes are simulated. During the second phase, the temporal feedbacks will be investigated. In this investigation, the developed model will be used to simulate recurring intense precipitation events and the effect on a landscape.
Figure 2 On overview of the processes that we will include in an integrated model.
In summary, natural hazards take place simultaneously and show complex interactions and behaviors. To increase understanding of hazardous processes, an integrated approach to modelling is needed. We want to help the development of the tools to analyze multi-hazard events in a holistic manner. Based on these tools, long-term temporal behavior can be investigated, which can aid disaster-preparedness.