Flood risk (d)evolution: Disentangling key drivers of flood risk change with a retro-model experiment

Abstract

Flood risks are dynamically changing over time. Over decades and centuries, the main drivers for flood risk change are influenced either by perturbations or slow alterations in the natural environment or, more importantly, by socio-economic development and human interventions. However, changes in the natural and human environment are intertwined. Thus, the analysis of the main drivers for flood risk changes requires a disentangling of the individual risk components. Here, we present a method for isolating the individual effects of selected drivers of change and selected flood risk management options based on a model experiment. In contrast to purely synthetic model experiments, we built our analyses upon a retro-model consisting of several spatio-temporal stages of river morphology and settlement structure. The main advantage of this approach is that the overall long-term dynamics are known and do not have to be assumed. We used this model setup to analyse the temporal evolution of the flood risk, for an ex-post evaluation of the key drivers of change, and for analysing possible alternative pathways for flood risk evolution under different governance settings. We showed that in the study region the construction of lateral levees and the consecutive river incision are the main drivers for decreasing flood risks over the last century. A rebound effect in flood risk can be observed following an increase in settlements since the 1960s. This effect is not as relevant as the river engineering measures, but it will become increasingly relevant in the future with continued socio-economic growth. The presented approach could provide a methodological framework for studying pathways for future flood risk evolvement and for the formulation of narratives for adapting governmental flood risk strategies to the spatio-temporal dynamics in the built environment.

Towards a more systemic understanding of flood risks

“…Another explanation could be to assign the responsibility for the observed limited risk reduction to climate change or the change of exposure and vulnerability of people and assets. This is supported by evidence for influences of environmental and societal drivers of change from various studies (e.g., Zischg et al, ).…”

Mapping the Sensitivity of Population Exposure to Changes in Flood Magnitude: Prospective Application From Local to Global Scale

“…The application of this method on the local scale is based on hydraulic simulations and synthetic hydrographs describing a wide range of flood magnitudes. The synthetic hydrographs were derived from the analysis of typical flood events and typical shapes of hydrographs and flood peak-volume relationships were extracted from historic flood events to be used for scaling the flood magnitude as outlined in Zischg et al (2018a) and Zischg et al (2018c). The synthetic hydrographs with increasing flood magnitudes were subsequently used to elaborate a set of inundation maps that can be overlaid with population data.…”

Alpine Water – common good or source of conflicts?

“…Although flooding hazards are well known and understood, rising land prices have caused residential and industrial areas to be established in flood-prone areas. Where once wetlands or seasonal pastures provided retention room for flood water, expensive and vulnerable assets now need to be protected from flooding (Zischg et al 2018). As figures from Austria show, this trend is still continuing (Fig.…”