Hydrology, Cryosphere & Earth Surface Meeting Report

How Much Land Surface Is Under Water at Any Given Time?

NASA Workshop on Remote Sensing of Inundation Extent; Boulder, Colorado, 21–22 May 2018

By and J. Toby Minear

Measurement of inundation extent in rivers, lakes, reservoirs, and wetlands is of vital importance to addressing scientific and societal problems ranging from flood prediction to quantification of the global carbon cycle. Boundaries between dry land and open water extend for long distances, and they change over time, so ground-based measurement of inundation extent is difficult. Instead, remote sensing is a promising way to comprehensively monitor surface water extent at large spatial scales.

Recent deployment of satellite-based sensors capable of measuring inundation extent—such as the Landsat Operational Land Imager (OLI), Phased Array type L-band Synthetic Aperture Radar (PALSAR), and Sentinel-1 and –2 and the anticipated launch of new missions, including NASA’s Surface Water and Ocean Topography (SWOT) and the joint NASA–Indian Space Research Organisation’s (ISRO) Synthetic Aperture Radar (NISAR) missions—presents an opportunity to reimagine monitoring inundation extent from space.

At a workshop held at the University of Colorado, more than 30 U.S. and international scientists discussed the potential for global inundation extent data products, and they developed recommendations for relevant government agencies. Meeting participants identified key science questions requiring inundation extent measurements, assessed capabilities of current remote sensing products, and explored the potential for advances in inundation measurement. Attendees had expertise in remote sensing methods development, global hydrology, aquatic ecology, carbon cycle science, and flood modeling.

The meeting produced five key recommendations:

  • Participants strongly urge all space agencies to develop and maintain free and open data policies because global inundation extent measurement depends on making mosaics from many images acquired across space and time.
  • Space agencies from the United States, Europe, France, Japan, and Canada maintain or are developing satellite instruments capable of measuring inundation extent and other variables critical to understanding inland and coastal water bodies. To optimally leverage these tools, attendees recommend that surface water hydrologists and their sponsors create an Inland Waters Science Team to coordinate science and data product development internationally.
  • This science team should use data from synthetic aperture radar, passive microwave, and optical instruments to develop consistent, dynamic, global inundation extent products in open water and vegetated environments at high temporal resolution. An effort to develop consistent products will benefit and will later use measurements from future missions like SWOT, NISAR, and Sentinel sensors and other optical and radar missions scheduled for launch in the next decade.
  • Current inundation extent products are often not well validated. Participants recommended development of a system of inundation extent validation sites and data sets including extensive airborne and ground-based measurements. This network should include sites for long-term monitoring and intensively instrumented campaigns focused on individual events, such as major floods. It could be coordinated through the Inland Waters Science Team.
  • Attendees recommend focused development of two static data sets critical to global inundation science: a high-resolution, global floodplain digital elevation model with submeter vertical accuracy and a very high spatial resolution (<5 meter) data set of maximum and minimum open water extent based on optical imagery.

The workshop was supported by the NASA Terrestrial Hydrology Program, with travel organized by ATA Aerospace LLC. It was generously hosted by the Cooperative Institute for Research in Environmental Sciences at the University of Colorado.

—Tamlin M. Pavelsky (email: [email protected]), Department of Geological Sciences, University of North Carolina at Chapel Hill; and J. Toby Minear, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder

Citation: Pavelsky, T. M., and J. T. Minear (2018), How much land surface is under water at any given time?, Eos, 99, https://doi.org/10.1029/2018EO104135. Published on 15 August 2018.
Text © 2018. The authors. CC BY-NC-ND 3.0
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