Research

Evaluating climate change adaptation options for urban flooding in Copenhagen based on new high‐end emission scenario simulations

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Abstract

Climate change adaptation studies on urban flooding are often based on a model chain approach from climate forcing scenarios to analysis of adaptation measures. Previous analyses of impacts in Denmark using ensemble projections of the A1B scenario are supplemented by two high‐end scenario simulations. These include a regional climate model projection forced to a global temperature increase of 6 degrees as well as a projection based on the RCP8.5 scenario. With these scenarios projected impacts of extreme precipitation increase significantly. For extreme sea surges the impacts do not seem to change substantially. The impacts are assessed using Copenhagen as a case study. For both types of extremes large adaptation measures are essential in the global six degree scenario; dikes must be constructed to mitigate sea surge risk and a variety of measures to store or convey storm water must be implemented as well as new paradigms for city planning to mitigate the impact of change in extreme precipitation risk. For both hazards business‐as‐usual are not possible scenarios, because large autonomous adaptation will occur in lack of suitable policy‐driven changes. Copenhagen has developed an adaptation plan to pluvial flooding that makes the urban areas more robust and reduces the risk of flooding in current climate to a very low level. The economic benefit in the A1B scenario is substantial, and even in the 6 degree scenario the frequency of flooding is not much higher than national recommendations today. The expected annual damage in the six degree scenario will be higher than today because the size and frequency of extreme events will increase.