A coupled approach to regional flood and land-use modeling to determine the impact of land-use-change and mitigation strategies on flood risk reduction

Abstract

Flooding is already one of the most devastating natural hazards when it comes to damage caused. A key factor for damage caused by flooding is the urbanization of floodplains. The high-density characteristic of urban development entails a high monetary value at risk. It also implies a high quantity of impervious areas furthering the intensity of occurring floods. With predicted future demographic and population growth these metropolitan areas are likely to increase. This will further negatively impact the potential flood loss. Estimations suggest an increase of up to US$ 63 Trillion of value at risk within the global 1 in 100-year floodplain by 2050. Climate change is adding further pressure on future flood risk by increasing the intensity and frequency of severe flood events. Therefore, prudent flood risk management is vital to mitigate these future threats. This includes an increased importance of regional development planning in risk management. Technically, the implementation of land use planning as a mitigation strategy leads to a two-way interaction between flood and land use change models. In addition, the application of other mitigation choices is spatially limited to small areas within a region. To model and test the placement of such options an upscaling is necessary. Also, when dealing with future change, uncertainty needs to be considered. Local uncertainty is a problem in the results of standard land use models, dealt with by using statistical approaches to follow the allocation of different land use classes across the region of interest. This thesis is organised in three publications dealing with the challenges of modelling regional flood risk in a distant future. The first paper introduces a computational framework to model the effect of land use planning as part of a mitigation strategy. This allows for the consideration of land use and climate change as drivers in future flood risk. The second paper investigates the use of portfolios of nature-based solutions (NBSs), as another land use-based mitigation option, in a regional planning application. For this purpose, rules of allocation to identify suitable locations were developed and tested to determine the tradeoffs between portfolio size and corresponding effect on flood impact. In this case NBS portfolios are used to overcome the difference in spatial resolution in land use planning and the traditional modelling of NBSs. The final paper introduces a framework using a range of approaches to deal with uncertainty to investigate the impact of local uncertainty in land use change on future value at stake and the impact on future flood risk. The approaches include a baseline with uncertainty being not considered, a most likely, a most valuable, and a weighted average scenario. The key findings of this thesis are the importance of using an integrated computational framework that considers plausible changes in the flood-land use nexus explicitly with the aid of linked, dynamic flood and land use models. It also provides a proof of concept of the consideration of portfolios of NBSs for flood risk reduction at the regional scale and highlights the value of and the necessity to include uncertainties in future land use as part of flood risk assessments.