NH
Natural Hazards

Multihazard

NH10 Multi-Hazards: The Latest EGU Natural Hazards Sub-Division

NH10 Multi-Hazards: The Latest EGU Natural Hazards Sub-Division

Earlier this year, the EGU Natural Hazards Division approved the addition of a new sub-division focused on the theme of ‘multi-hazards’. The Science Officers representing this sub-division, Joel Gill (British Geological Survey) and Marleen de Ruiter (IVM-VU Amsterdam), reflect on why this sub-division is necessary and how you can get involved.

Many regions are affected by multiple natural hazards, with hazards and/or their impacts not always occurring independently. The Sendai Framework for Disaster Risk Reduction, therefore, advocates for ‘multi-hazard’ approaches to disaster risk assessment and reduction. The UN defines ‘multi-hazard’ as follows: 

“Multi-hazard means (1) the selection of multiple major hazards that the country faces, and (2) the specific contexts where hazardous events may occur simultaneously, cascadingly or cumulatively over time, and taking into account the potential interrelated effects” (UNDRR Terminology, 2017).

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Multi-Natural-Hazards: how can we deal with such complex chain of events?

Multi-Natural-Hazards: how can we deal with such complex chain of events?

Today we have the honor to have Prof. Victor Jetten as our guest. Throughout his career Victor, has been working in modelling of natural hazard and land degradation processes. Starting with biomass and grazing capacity, the effects of logging on the natural rain forest water balance, he then moved to soil erosion and land degradation processes as a result of land use change and overgrazing. He believes that all these processes should not be studied and modeled as separate disciplines but in a much more holistic way. In the context of Natural Disasters stakeholders are confronted with chains of multiple hazards: such an earthquake leading to landslides leading to blockage of river systems leading to flash floods (such as happened in Wenchuan in 2008 and Nepal in 2016). Each subsequent extreme rainfall triggers landslides and extreme erosion, forging possibly more change in these areas than several decades of climate change, and wiping out years of development. Victor thinks science has to be useful for society and his aim is to provide timely and actionable spatial information in disaster preparedness, prevention and response. To this end he develops together with PhD researchers the opensource model openLISEM, that is able to simulate runoff, river discharge, floods, erosion and deposition and debris flows, in an integrated and spatially detailed way.

 

  1. Today we are going to talk about multi-hydromorphic-hazards. Victor, what can you tell us about it?

We have moved from theory and models to understand processes in nature to the application of that knowledge in a hazards context (as a result of triggers such as extreme weather events or earthquakes). The probability of that event was added, to serve stakeholders better. But things become complicated very rapidly: we almost never know the probability of the event itself, so we exchanged that for the probability of the driving process, which is not the same. Hazards happen at the same time or as a chain of events: the 2008 earthquake in Wenchuan had direct earthquake damage, triggered over 100000 landslides, hundreds of which dammed rivers that potentially led to flash floods. Flash floods are triggered after an el Nino year because the sparse vegetation led to overgrazing. This complexity gives us problems: we have different models for different processes made by separate groups of scientists: geomorphologists look at landslides, hydrologists at flooding (but not so much at sediment in floods and where sediment comes from), erosion is the domain of soil scientists and agriculture (but floods are far downstream), meteorologists focus on the weather part of hazards. This is perfectly natural as each of these are sciences in itself. But now you live on a Caribbean island and are hit by a hurricane. Your house is subject to sea surges, wind damage, flash floods and landslides. These effects are aggravated because of a lack of landscape management that gradually filled up the river channels with sediment. Who will help you? An army of scientists that each speak their own language! And of course the solutions are in spatial planning and governance, which are again separate sciences.

 

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