Comparing green infrastructure as ecosystem-based disaster risk reduction with gray infrastructure in terms of costs and benefits under uncertainty: A theoretical approach

The Eco-DRR (ecosystem-based disaster risk reduction) is attracting attention as infrastructure that substitutes “gray” or built infrastructure, owing to its attractive characteristics such as lower costs of introduction and maintenance, provision of various ecosystem services, and local community development, among others. On the other hand, gray infrastructure is still a central measure of DRR, as there is a comprehensive understanding of its design and functioning against natural hazards. The argument about the use of green infrastructure instead of gray infrastructure in many aspects of DRR raises an important question: under what circumstances is green infrastructure more desirable? This paper uses a theoretical approach to provide an exact condition under which introducing green infrastructure is desirable, taking into consideration the aspect of uncertainty in deriving the optimal size of green infrastructure and the disaster risk (or expected damage). Under optimal green infrastructure, we show an exact level of the population, under which using Eco-DRR is preferable to gray infrastructure, expressed by parameters reflecting the probability of occurrence of hazard, probability of preventing exposure to the hazard, population size, and vulnerability to damage accruing from exposure, as well as costs and benefits of the two infrastructures. Our results provide useful information regarding policy decision-making about whether to adopt gray or green infrastructure in an area, by applying the results to various cases by assuming the exact values of the parameters.