This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A false sense of security can be dangerous. The "Safe Development Paradox" is a phenomenon in which flood-control infrastructure makes people feel safe, so communities subconsciously start building closer and closer to historically vulnerable lowlands.
We can study this effect by looking at where people settled before and after the infrastructure was built. Researchers at the International Research Institute of Disaster Science (IRIDeS), Tohoku University and Meijo University compared Meiji-era natural landscapes and the distribution of built-up areas with present-day conditions. Their flood simulations and analyses offer a picture of what it takes to keep people safe.
The work is published in the Journal of Hydrology: Regional Studies. Focusing on historically flood-prone Marumori Town in Miyagi Prefecture, Japan, the researchers examined how construction over the past century could have altered the severity of flooding or exposure to it. Evaluating how these physical changes affected flooding has been challenging because rainfall patterns, river structures and urban growth have all changed simultaneously.
To measure the impact of human-made structural changes, the researchers used detailed computer simulations and old maps to recreate and study the original natural landscape. "By looking back at conditions in the Meiji era as a natural baseline, we can use models to determine whether the flood prevention infrastructure we installed is helping," says Nilo Lemuel J. "Surprisingly, we discovered that these 'upgrades' might have made things worse in some cases." It may sound counterintuitive, but installing infrastructure to reduce flooding can sometimes make it worse.
Human-made walls along rivers called levees are designed to keep swollen rivers from spilling over during heavy rain and extreme weather events. During lighter rain, however, the same walls meant to protect us can trap rainwater inside neighborhoods, causing worse inland flooding than occurred over a century ago. During heavy storms with widespread flooding, the simulations suggested that levees reduced flood volumes.
But during light rain, when flooding is limited, flood volumes increased. Further analysis revealed a tipping point beyond which modern terrain modifications shift from mitigating flood depths to making them worse. Assessing where that tipping point lies for each body of water may be key to deciding whether flood-prevention infrastructure is necessary.
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