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Avoiding Damage Costs from Urban Floods with Nature-Based Solutions : Dublin Case Study

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Title: Avoiding Damage Costs from Urban Floods with Nature-Based Solutions : Dublin Case Study
Author(s): Raschen, Annika
Contributor: University of Helsinki, Faculty of Agriculture and Forestry
Degree program: Master´s Programme in Agricultural, Environmental and Rescource Economics)
Specialisation: Environmental and Natural Resource Economics
Language: English
Acceptance year: 2021
This thesis studies the economic benefits that the installation of nature-based solutions can have as a flood risk management tool. The effects of a changing climate often accumulate in urbanised areas and can translate into an increased likelihood and heightened damage potential of precipitation-induced flood events. One way to reduce the devastating flood impact is the use of nature-based solutions, which are management tools relying on natural processes and ecosystem services (EC, 2018). Green roofs are one example of nature-based solutions. To date, little research is available in the academic literature on the economic profitability and cost-efficiency of such alternative approaches (Palmer et al., 2015). The thesis aims to contribute to the scare literature on the topic by conducting a flood damage assessment for a case study site. It is devel-oped from a research contribution to the EU OPERANDUM project, which evaluates nature-based solutions as tool to alleviate hydro-meteorological risks as well as their cost-efficiency on a broader scale (OPERANDUM Project, 2018). The thesis conducts a flood dam-age assessment for green roofs hypothetically installed in Dublin, Ireland. It estimates the expected damage costs from flood scenarios with a recurrence period of 10, 100 and 1000 years. To this end it relies methodologically on a flood damage assessment, specifically the Joint Research Centre model developed by Huizinga, de Moel & Szewczyk (2017), as well as on value transfer. The assessment is re-stricted to the calculation of direct, tangible flood damages. To provide more robust results, the assessment also draws on the analytical insights from the cost-benefit analysis literature and incorporates aspects such as discounting and a partial sensitivity analysis. In terms of software, the majority of the research is carried out in QGIS and Excel. Comparing the flood impacts with and without the installation of nature-based solutions, it assesses the size of the avoided damage costs and finds a noticeable positive impact of green roofs. The green roofs cannot only reduce the size of the flooded areas by up to 19% as well as decrease the water depth in the still inundated parts, but also noteworthily curtails the height of the direct, tangible flood damage costs. The thesis cannot extract definite conclusions on the profitability of green roofs in the sense of providing a net present value, because it does not study costs nor other benefits of green roofs for reasons of scope. It does, however, show that the installation of green roofs can lower the flood damage costs in Dublin by up to 36%. As additional conclusion, this thesis calls for research into more nuanced flood damage assessment methods, since the selected model excluded many factors. A methodological refining could increase the precision of monetary damage estimates. Altogether, the thesis observes that green roofs can be a useful tool to reduce the devastating impact of urban floods. However, green roofs should be combined with other flood management tools, since they can be insufficient if applied on their own.
Keyword(s): Nature-based Solutions Flood Damage Assessment Green Roofs Value Transfer Cost-Benefit Analysis

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