Satellite observations indicate increasing proportion of population exposed to floods

Abstract

Flooding affects more people than any other environmental hazard and hinders sustainable development1–3. Investing in flood adaptation can reduce loss of life and livelihoods 4,5. However, where and how floods occur, and who is exposed, is changing due to rapid urbanization 6, new flood mitigation infrastructure 7,8, and increasing human settlements in floodplains9. Previous studies estimating population exposed to floods are limited by lack of observational data, relying instead on global models with high uncertainty4,10–14. Here we use nearly two decades of daily satellite imagery at 250 meter resolution (MODIS) to develop new estimates of flood extent and population exposure for 913 large flood events from 2000-2018, estimating 2.23 million km2 of flooded area and 290 million people directly affected. We find the at least 86 million people newly settled in a location where satellites observed inundation in the past 20 years. This represents a 20% increase in the proportion of population exposed to floods, ten times higher than previous estimates10. Near-future climate change projections (2030), indicate the proportion of population exposed to floods will continue to expand. Our findings can aid prioritization of global flood adaptation investment and inform adaptation strategies, from insurance to managed retreat, at local scales15–17. As satellite coverage and resolution increase, we anticipate observation of flood events to aid understanding where floods change and how to adapt. This flood event database will contribute to improved accuracy of global and local flood models, vulnerability assessments, efficacy of adaptation intervention, and understanding interactions of land change, climate, and floods.

DSWEmod — The Production of High‐Frequency Surface Water Map Composites from Daily MODIS Images

“…2020), large‐scale flood hazard assessments (Tellman et al. 2020), and global raster water masks (Carroll et al. 2009) are a few of the additional applications that can be readily generated from publicly available DSWEmod code and/or products (Soulard et al.…”

“…DSWEmod can be fused with Landsat DSWE methods or extended to include Sentinel-2 to either generate even more complete records or to potentially help identify finer-scale features (Zhang et al 2014;Singh et al 2020;. National wetland mapping (Vanderhoof et al 2020), large-scale flood hazard assessments (Tellman et al 2020), and global raster water masks (Carroll et al 2009) are a few of the additional applications that can be readily generated from publicly available DSWEmod code and/or products (Soulard et al 2021).…”

Estimating Population and Urban Areas at Risk of Coastal Hazards, 1990–2015: How data choices matter

“…Local studies (Schumann and Bates, 2018;Orton et al, 2020) suggest clearly that the hydrodynamics of the coastal zone are complex and nuanced, perhaps even more so in urban areas where impervious surface, underground infrastructure (sewage and subway systems), and other modifications to the landscape (including accumulations of uncollected solid waste) may impact inland flows and drainage. New work on coastal storm surges and tidal heights (Muis et al, 2020;Arns et al, 2020) and empirical flood events (Tellman et al, 2020) make new 150 avenues of research possible in the coming years, but currently hydrodynamic modeling has been restricted to certain locations or events. (Tadono et al, 2014) https://doi.org/10.5194/essd-2021-165…”

“…Since the construction of the first LECZ (McGranahan et al, 2007), others have adopted the basic methodology to create improved data for more local areas (Reimann et al, 2018;Vafeidis et al, 2019;Hauer et al, 2020), as a basis for forecasting future exposure (Reimann et al, 2018;Neumann et al, 2015), and at finer elevation bands (Lichter et 1195(Lichter et al, 2010). But the international norms and data available to model coastal flooding and sea level rise are presently emerging (Nicholls et al, 2021;Muis et al, 2020;Tellman et al, 2020;Vafeidis et al, 2019;Haigh et al, 2020;Kopp et al, 2015;Tebaldi et al, 2012), and to date mostly depend on local data.…”

How can Changes in the Human‐Flood Distance Mitigate Flood Fatalities and Displacements?

“…To investigate changes in human‐flood distance over a specified time period (2000–2018), we utilize spatiotemporal population data along with global flood inundation data (GFD, Tellman et al. (2021a)). These data sets are chosen based on their availability and coverage for the selected timeframe.…”