Climate Change adaptation of urban drainage systems using the Resilience Framework Approach – Case study in Dordrecht, Netherlands
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While flooding is the most common natural hazard and third most damaging after storms and earthquakes, climate change is likely to exacerbate the issue. In the Netherlands, regional climate projections predict increases in rainfall intensity, which are likely to cause more frequent and severe floods, thereby putting people and assets increasingly at risk. The projected impacts and uncertainties associated with climate change therefore reveal the need for urban planners and water managers to plan ahead and anticipate extreme weather events. Traditional approaches to storm water management present shortcomings such as statistical uncertainties and limited flexibility for modifying a selected adaption strategy to future climatic variability. In this study, an emerging approach termed the resilience framework approach (RFA) was tested on Dordrecht’s drainage systems, and presented as an alternative approach to storm water management. The RFA builds on already existing approaches, while enhancing the flexibility of climate adaptation strategies to future climatic variability, and takes opportunity of urban renewal to perform the drainage system’s retrofit. The RFA was applied to Dordrecht’s drainage systems in order to evaluate the systems’ resilience and adaptation potential to climate change. More specifically, the aim of the study was to determine thresholds for the desired level of system performance, and to determine how much climate change the current drainage systems could cope with before exceeding those thresholds. A set of adaptation measures was researched and tested to determine if the resilience of the drainage system to climate change would be enhanced. The adaptation measures were tested in this study were: the incremental change strategy, which consisted of disconnecting 40% of open paved roads and flat roofs from the sewer system by 2045, and the transformational change strategy, which consisted of using the overland drainage system. The windows of opportunities identified to perform the system retrofit were scheduled road and building maintenance. The quantification of the current and proposed modified drainage systems’ response to climate change was performed using a geographical information system (ArcGIS) and two hydrodynamic-hydraulic models (DORD-BAS, 1D and DORD_ODS, 1D2D). The results showed that the incremental change strategy was effective in most districts, but not all. Under synthetic rainfall designs, only 60% to 65% of the districts showed considerable improvement, that is, the proposed modified sewer system could cope with more rainfall than the current sewer system. Results for the transformational change strategy were positive for two out of three districts, that is, with an adapted terrain, less buildings flooded. These results provide great insight into the capacity of the proposed modified drainage system to deal with the impacts of climate change. However, more research is needed to find adaptation measures that will increase the entire sewer system’s resilience to climate change. Moreover, additional research should be performed on the use of the overland drainage system, since only three districts were evaluated in this study. In conclusion, the contributions of the RFA to storm water management are 1) its capacity to cope with uncertainty, 2) the flexibility of adaptation strategies to future changing climate, and 3) the use of windows of opportunity, such as urban renewal, in the development of adaptation strategies. Moreover, the RFA facilitates the development of responses and adaptation measures that are appropriate at the right time and place. The results of this study show that the RFA can contribute to the adaptation of urban drainage systems to climate change. The RFA can be considered as an alternative or complementary approach to already existing approaches in storm water management.