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Climate change has intensified extreme rainfall events which have made flood risk management critical for cities (IPCC, 2023). Conventional drainage systems are struggling to cope with increased stormwater flows, leading to sewer overflows and localised flooding (Ashley et al., 2020). A shift towards resilient flood management is needed, focusing on polycentric governance, integrated management, distributed infrastructure and multifunctional measures (Franco-Torres et al., 2021). Spatial planning plays a key role by integrating sectors (water management, environmental planning, transportation), coordinating policies and providing a framework to systematise incremental interventions (Davoudi et al., 2010).
There are gaps in the implementation of resilient flood risk management in planning practice (Dorst et al., 2021). In this context, knowledge production plays a crucial role in shaping flood management approaches and solutions. Indeed, the analyses carried out in the early stages of planning activities provide an opportunity to highlight the shortcomings of existing infrastructure and to advocate for change. A comprehensive analytical framework is needed to address the multiple dimensions of urban drainage, including surface and subsurface layers and different rainfall events. Through this framework, benefits beyond flood mitigation can be introduced into the urban environment.
However, there has been little research on such a framework at the urban scale. Therefore, this study proposes a composite index to analyse how cities cope with different rainfall events. The intent of the index is to capture three different urban capacities connected to flood management: (i) the capacity of an urban system to manage runoff during light rainfall; (ii) the capacity to prevent infrastructure failure during moderate rainfall; (iii) and the capacity to mitigate damage during extreme rainfall. The study also examines whether synergies or trade-offs exist between these capacities.
The study applies a quantitative methodology to Varese, a medium-sized city in northern Italy, by using the ecosystem services framework to assess the three capacities: (i) source control, (ii) local retention and (iii) flood mitigation, as part of the ecosystem service "water cycle and flow mitigation" (WCFM). These capacities are assessed using three models: InVEST from the Natural Capital Project, SWMM from the Environmental Protection Agency and HEC-RAS from the US Army Corps of Engineers. By integrating these models, the study provides a comprehensive view of (i) areas with the highest runoff throughout the year, (ii) nodes where grey infrastructures are most vulnerable to failure during moderate rainfall, and (iii) areas where stormwater accumulates during extreme events.
The study aggregates the results of the three models on the census track. Three indicators are then calculated: (i) runoff as a percentage of total rainfall, (ii) node failure density, (iii) flood risk. These results are then normalised and combined to create a composite index of the WCFM demand in Varese. The study defines priority areas for action through a hotspot analysis. A Spearman's rank correlation coefficient is used to identify synergies and trade-offs between the three indicators.
Results show almost no spatial correlation between the three indicators. This could be interpreted by the fact that they represent different phenomena that contribute separately to the demand for WCFM. There is a need to consider each dimension to provide a more comprehensive evidence base for prioritising action. Nevertheless, through the composite index and hotspot analysis, the study can identify priority areas and characterise them according to the composition of the index. This characterisation allows for more targeted interventions when developing planning strategies.
This study contributes to the growth of methodological knowledge by developing a composite index that integrates several models to assess stormwater management. It also creates practical knowledge that can guide planners in identifying priority areas for improving the effectiveness of multifunctional measures.
References
Ashley, R., Gersonius, B., & Horton, B. (2020). Managing flooding: From a problem to an opportunity. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 378(2168), 20190214. https://doi.org/10.1098/rsta.2019.0214
Davoudi, S., Jenny, C., & Abid, M. (Eds.). (2010). Planning for Climate Change: Strategies for Mitigation and Adaptation for Spatial Planners (Vol. 2). https://www.emerald.com/insight/content/doi/10.1108/ijccsm.2010.41402aae.001/full/html
Dorst, H., Van Der Jagt, A., Runhaar, H., & Raven, R. (2021). Structural conditions for the wider uptake of urban nature-based solutions – A conceptual framework. Cities, 116, 103283. https://doi.org/10.1016/j.cities.2021.103283
Franco-Torres, M., Rogers, B. C., & Harder, R. (2021). Articulating the new urban water paradigm. Critical Reviews in Environmental Science and Technology, 51(23), 2777–2823. https://doi.org/10.1080/10643389.2020.1803686
IPCC. (2023). Climate Change 2022 – Impacts, Adaptation and Vulnerability: Working Group II Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (1st ed.). Cambridge University Press. https://doi.org/10.1017/9781009325844
| Keywords | Resilient Flood Management, Stormwater Management, Adaptation, Ecosystem Services, Urban indicators |
|---|---|
| Best Congress Paper Award | No |
