standard Keep the light on: Using night lights to identify flood vulnerability

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Earth at night. (NOAA)

Similar to other geohazards, floods are unpredictable and complex. This makes preparing for them challenging especially for communities that deal with unexpected or unforeseen flood events that may occur. Flooding is an interesting case study for understanding how geohazards and society interact which can have disastrous consequences if little preparation is made in advance. As far as floods in society are concerned they are usually understood in terms of risk, such as the likelihood that someone’s home or business may be flooded.

If the flood risk is low perhaps little is done to mitigate flooding. In some situations insurance can be purchased to cover extreme events if they should happen, but little is done overall. If the risk is perceived as high or of concern to an individual, community, county or nation, then usually flood mitigation efforts, including research, should be prioritised. If flood risk is high it begs the question why is this the case? This comes down to exposure and vulnerability.

If property or people themselves are exposed to the flood hazard, with little to no flood protection, they are at risk of losing their home, business, livelihood, way of life or even their lives. But better ways of identifying flood vulnerability are needed to help make communities resilient to flood hazards.

Professor Alberto Montanari from the University of Bologna visited IHRR recently to give a seminar on the damages and fatalities caused by flooding that has been increasing in countries throughout the world. As a hydrologist, a scientist who studies the movement, distribution and quality of water, he presented some of his recent work in identifying areas of flood vulnerability in Italy. He said ‘that flood vulnerability and frequency are intimately connected’, which includes the effects of climate change and other factors that affect flooding, such as land use.

The development of society over time influences the environment in profound ways transforming the pathways and flows of water, which can lead to flood hazards. Flooding in this sense is an interaction between the movement and distribution of water through the water cycle, and the societies that depend upon it for survival, but are also at risk of its damaging impacts. One clever way of identifying flood vulnerability presented by Montanari is using satellite observations of night time lights from homes or businesses, and combining them with river network data.

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Nightlight data (yellow) with river network data (blue) to quantify flood risk.

Since night lights are a useful indicator for human settlements it can be used to identify and prioritise vulnerable populations that live close to streams or rivers. The data presented by Montanari shows an increase in night lights in areas that are near rivers. In the case of countries in Asia the trends are especially pronounced. In North America the presence of night lights are actually decreasing but this could be due to the implementation of policies to reduce light pollution.

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Growth of nightlights around river networks.

If this data proves to be especially useful in identifying flood vulnerability should people who live near rivers keep the lights on at night? As development increases so do human settlements in areas that may be more vulnerable to hazards such as flooding. Night light data at the very least provides an indicator of how development and hydrological change come together. Montarnari is interested in integrating night light data with data on land use change, and changes in the shape of the landscape, as these together with other data also help determine flood vulnerability. Montanari said much of this comes down to the importance of data sharing in research.

Since the world has been and likely will continue to experience rapid, unexpected environmental change, Montanari argues that we must share data that could allow for more accurate modelling of environmental changes that have major consequences for human societies. Open data sharing is in many ways already revolutionising the sciences, and is of interest to anyone working in science, IT or creative industries, government and many other sectors. Making scientific data open source in order to identify flood vulnerability seems one of many reasons why researchers should move in this direction.

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