Floods cause billions of dollars of damage each year, and flood risks are expected to increase due to socio-economic development, subsidence, and climate change. Implementing additional flood risk management measures can limit losses, protecting people and livelihoods. Whilst several models have been developed to assess global-scale river-flood risk, methods for evaluating flood risk management investments globally are lacking. Here, we present a framework for assessing costs and benefits of structural flood protection measures in urban areas around the world. We demonstrate its use under different assumptions of current and future climate change and socio-economic development. Under these assumptions, investments in dykes may be economically attractive for reducing risk in large parts of the world, but not everywhere. In some regions, economically efficient investments could reduce future flood risk below today’s levels, in spite of climate change and economic growth. We also demonstrate the sensitivity of the results to different assumptions and parameters. The framework can be used to identify regions where river-flood protection investments should be prioritized, or where other risk-reducing strategies should be emphasized.
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Under the ‘constant absolute risk’ objective, B:C ratios exceed 1 for all RCPs combined with SSPs. However, for SSP, which represents a more fragmented world, the B:C ratios are less than, because under this scenario, economic prospects are poor and thus the benefits of adaptation low. Under the ‘constant absolute risk’ objective’, B:C ratios exceed 1 for all combinations of RCPs and SSPs.
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In this study, we used Representative Concentration Pathways (RCPs) and Shared Socioeconomic pathways (SSPs)2 to represent future climate and changes in future socioeconomic conditions, respectively. In total, there are 4 RCPs and 5 SSPs, leading to a matrix of 20 combinations of projections.
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For the ‘optimise’ objective, there is a large difference between the RCP/SSP combinations in both the benefits and the costs. The costs at the global scale range from USD 22 billion per year (RCP2.6/SSP3) and 78 billion USD per year (RCP8.5/SSP5). Averaged across all SSPs, the results show that the costs at the global scale increase as the CO2-equivalent concentration increases (RCP2.6 = USD 40 billion per year; RCP4.5 = USD 45 billion per year; RCP6.0 = USD 47 billion per year; RCP8.5 = USD 55 billion per year). This means that globally, higher greenhouse gas concentrations will lead to higher adaptation costs as a result of a generally larger increases in flood hazard (note that there are also areas where higher greenhouse gas emissions lead to reduction in flood risk). For all combinations of RCP/SSP, on average, the benefits far outweigh the costs, leading to B:C ratios ranging from 3.6 (RCP2.6/SSP3 and RCP4.5/SSP3) to 10.2 (RCP8.5/SSP5). The B:C ratios are also larger for the RCPs with higher CO2 concentrations, since the larger increase in hazard under those RCPs means that flood damage is higher, and therefore the potential avoided damage is also higher. Averaged across all RCPs, the costs at the global scale follow the projected increases in GDP to 2080 between the different SSPs (i.e. highest costs in SSP5 and lowest costs in SSP3, which are the SSPs with the highest and lowest global GDP growth respectively).Under the ‘constant absolute risk’ objective, B:C ratios exceed 1 for all RCPs combined with SSPs. However, for SSP, which represents a more fragmented world, the B:C ratios are less than, because under this scenario, economic prospects are poor and thus the benefits of adaptation low. Under the ‘constant absolute risk’ objective’, B:C ratios exceed 1 for all combinations of RCPs and SSPs.
Percentage reduction in current expected annual damage for simulations carried out with assumed current protection standards compared to no flood protection
B:C ratio at sub-national level, and percentage of models for which B:C ratio exceeds 1, for the EAD-constant and EAD/GDP-constant adaptation objections
Protection standards at sub-national level in 2080 and associated B:C ratios
by Philip J. Ward, Brenden Jongman, Jeroen C. J. H. Aerts, Paul D. Bates, Wouter J. W. Botzen, Andres Diaz Loaiza, Stephane Hallegatte, Jarl M. Kind, Jaap Kwadijk, Paolo Scussolini & Hessel C. Winsemius
Nature Climate Change http://www.nature.com
Published online 31 July 2017
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