Roughness coefficients for densely vegetated flood plains /

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Coproducing flood risk management through citizen involvement: insights from cross-country comparison in Europe

Across Europe, citizens are increasingly expected to participate in the implementation of flood risk management (FRM), by engaging in voluntary-based activities to enhance preparedness, implementing property-level measures, and so forth. Although citizen participation in FRM decision making is widely addressed in academic literature, citizens’ involvement in the delivery of FRM measures is comparatively understudied. Drawing from public administration literature, we adopted the notion of “coproduction” as an analytical framework for studying the interaction between citizens and public authorities, from the decision-making process through to the implementation of FRM in practice. We considered to what extent coproduction is evident in selected European Union (EU) member states, drawing from research conducted within the EU project STAR-FLOOD (Strengthening and Redesigning European Flood Risk Practices towards Appropriate and Resilient Flood Risk Governance Arrangements). On the basis of a cross-country comparison between Flanders (Belgium), England (United Kingdom), France, the Netherlands, and Poland, we have highlighted the varied forms of coproduction and reflected on how these have been established within divergent settings. Coproduction is most prominent in discourse and practice in England and is emergent in France and Flanders. By contrast, FRM in the Netherlands and Poland remains almost exclusively reliant on governmental protection measures and thereby consultation-based forms of coproduction. Analysis revealed how these actions are motivated by different underlying rationales, which in turn shape the type of approaches and degree of institutionalization of coproduction. In the Netherlands, coproduction is primarily encouraged to increase societal resilience, whereas public authorities in the other countries also use it to improve cost-efficiency and redistribute responsibilities to its beneficiaries.

Dealing with flood damages: will prevention, mitigation, and ex post compensation provide for a resilient triangle?

There is a wealth of literature on the design of ex post compensation mechanisms for natural disasters. However, more research needs to be done on the manner in which these mechanisms could steer citizens toward adopting individual-level preventive and protection measures in the face of flood risks. We have provided a comparative legal analysis of the financial compensation mechanisms following floods, be it through insurance, public funds, or a combination of both, with an empirical focus on Belgium, the Netherlands, England, and France. Similarities and differences between the methods in which these compensation mechanisms for flood damages enhance resilience were analyzed. The comparative analysis especially focused on the link between the recovery strategy on the one hand and prevention and mitigation strategies on the other. There is great potential within the recovery strategy for promoting preventive action, for example in terms of discouraging citizens from living in high-risk areas, or encouraging the uptake of mitigation measures, such as adaptive building. However, this large potential has yet to be realized, in part because of insufficient consideration and promotion of these connections within existing legal frameworks. We have made recommendations about how the linkages between strategies can be further improved. These recommendations relate to, among others, the promotion of resilient reinstatement through recovery mechanisms and the removal of legal barriers preventing the establishment of link-inducing measures.

Assessment of Flood Risk Under Future Climate Conditions

Global climate change is predicted to have impacts on the frequency and severity of flood events. In this study, output from Global Circulation Models (GCMs) for a range of possible future climate scenarios was used to force hydrologic models for four case study watersheds built using the Soil and Water Assessment Tool (SWAT). GCM output was applied with either the "delta change" method or a bias correction. Potential changes in flood risk are assessed based on modeling results and possible relationships to watershed characteristics. Differences in model outputs when using the two different methods of adjusting GCM output are also compared. Preliminary results indicate that watersheds exhibiting higher proportions of runoff in streamflow are more vulnerable to changes in flood risk. The delta change method appears to be more useful when simulating extreme events as it better preserves daily climate variability as opposed to using bias corrected GCM output.

FLOOD RISK ASSESSMENT UNDER HISTORICAL AND PREDICTED LAND USE CHANGE USING CONTINUOUS HYDROLOGIC MODELING

Current procedures for flood risk estimation assume flood distributions are stationary over time, meaning annual maximum flood (AMF) series are not affected by climatic variation, land use/land cover (LULC) change, or management practices. Thus, changes in LULC and climate are generally not accounted for in policy and design related to flood risk/control, and historical flood events are deemed representative of future flood risk. These assumptions need to be re-evaluated, however, as climate change and anthropogenic activities have been observed to have large impacts on flood risk in many areas. In particular, understanding the effects of LULC change is essential to the study and understanding of global environmental change and the consequent hydrologic responses. The research presented herein provides possible causation for observed nonstationarity in AMF series with respect to changes in LULC, as well as a means to assess the degree to which future LULC change will impact flood risk. Four watersheds in the Midwest, Northeastern, and Central United States were studied to determine flood risk associated with historical and future projected LULC change. Historical single framed aerial images dating back to the mid-1950s were used along with Geographic Information Systems (GIS) and remote sensing models (SPRING and ERDAS) to create historical land use maps. The Forecasting Scenarios of Future Land Use Change (FORE-SCE) model was applied to generate future LULC maps annually from 2006 to 2100 for the conterminous U.S. based on the four IPCC-SRES future emission scenario conditions. These land use maps were input into previously calibrated Soil and Water Assessment Tool (SWAT) models for two case study watersheds. In order to isolate effects of LULC change, the only variable parameter was the Runoff Curve Number associated with the land use layer. All simulations were run with daily climate data from 1978-1999, consistent with the 'base' model which employed the 1992 NLCD to represent 'current' conditions. Output daily maximum flows were converted to instantaneous AMF series and were subsequently modeled using a Log-Pearson Type 3 (LP3) distribution to evaluate flood risk. Analysis of the progression of LULC change over the historic period and associated SWAT outputs revealed that AMF magnitudes tend to increase over time in response to increasing degrees of urbanization. This is consistent with positive trends in the AMF series identified in previous studies, although there are difficulties identifying correlations between LULC change and identified change points due to large time gaps in the generated historical LULC maps, mainly caused by unavailability of sufficient quality historic aerial imagery. Similarly, increases in the mean and median AMF magnitude were observed in response to future LULC change projections, with the tails of the distributions remaining reasonably constant. FORE-SCE scenario A2 was found to have the most dramatic impact on AMF series, consistent with more extreme projections of population growth, demands for growing energy sources, agricultural land, and urban expansion, while AMF outputs based on scenario B2 showed little changes for the future as the focus is on environmental conservation and regional solutions to environmental issues.

EVALUATION OF NON-STATIONARITY IN ANNUAL MAXIMUM FLOOD SERIES OF MODERATELY IMPAIRED WATERSHEDS IN THE UPPER MIDWEST AND NORTHEASTERN UNITED STATES

United States federal agencies assess flood risk using Bulletin 17B procedures which assume annual maximum flood series are stationary. This represents a significant limitation of current flood frequency models as the flood distribution is thereby assumed to be unaffected by trends or periodicity of atmospheric/climatic variables and/or anthropogenic activities. The validity of this assumption is at the core of this thesis, which aims to improve understanding of the forms and potential causes of non-stationarity in flood series for moderately impaired watersheds in the Upper Midwest and Northeastern US. Prior studies investigated non-stationarity in flood series for unimpaired watersheds; however, as the majority of streams are located in areas of increasing human activity, relative and coupled impacts of natural and anthropogenic factors need to be considered such that non-stationary flood frequency models can be developed for flood risk forecasting over relevant planning horizons for large scale water resources planning and management.