Protecting Lives and Livelihoods Across Alaska With NASA Surface Water Data

The United States Geological Survey (USGS) traditionally relies on in situ monitoring stations to measure river flow and assess flood risks nationwide. However, in remote and rugged environments like Alaska, maintaining these stations is dangerous, expensive (costing up to $40,000 annually per station), and labor intensive, leaving many rivers unmonitored. To address this gap, several agencies, including USGS, submitted a request through the 2018 Satellite Needs Working Group (SNWG) survey, seeking a remote sensing solution to track surface water safely and efficiently, in concert with existing in situ networks.

In response to this need, NASA’s Observational Products for End-Users from Remote Sensing Analysis (OPERA) project at the Jet Propulsion Laboratory (JPL) collaborated closely with USGS to develop the Dynamic Surface Water Extent (DSWx-HLS) data product. By leveraging near-daily Harmonized Landsat and Sentinel-2 (HLS) satellite observations, another solution from SNWG, this new tool allows the USGS to remotely calculate river widths and estimate streamflow. This solution significantly reduces operational costs and personnel hazards while providing critical data in areas that were previously too difficult to monitor.

Today, USGS actively relies on DSWx-HLS data for operational streamflow monitoring in Alaska. While satellite data can not entirely replace traditional in situ monitoring, it successfully augments these efforts and fills critical gaps in data-sparse regions. By the end of 2025, USGS aimed to remotely monitor more than 30 sites using this NASA data. As the technology and methodologies continue to mature, they plan to eventually expand this remote monitoring network to over 70 sites.

The USGS supports communities in water management and flood risk reduction through observation of streamflow conditions. The scarcity of ground stations and stream gauges in many remote parts of Alaska has historically created obstacles to decision-making. This product directly supports emergency personnel and planners, in preparing for and responding to flood risks across Alaska, especially in those areas where in situ measurements are scarce. Flood early warning can protect life and property, while understanding streamflow conditions more generally supports water management decisions. This work also protects USGS personnel from having to install or service streamflow gauges in dangerous areas.

The Dynamic Surface Water Extent (DSWx-HLS) data product is the key product for meeting this need and was co-developed by NASA and USGS to fill critical gaps in sparse ground data regions. The combination of active sensor SAR and optical data from HLS allows more frequent detection and mapping of surface water extent.

This product leverages near daily Harmonized Landsat and Sentinel-2 (HLS) Observations to calculate surface water extent and estimate stream discharge. HLS seamlessly combines the longest continuous record of Earth observing data from Landsat with European Space Agency’s Sentinel satellite data and provides global Earth observations every 1.6 days. The use of SAR data from Sentinel 1, and eventually from NISAR, provides more frequent measurements of surface water extent, particularly in dark or cloudy conditions that commonly limit the number of available observations in high-latitude areas.

USGS relies on this product to estimate streamflow in this region, significantly reducing operational costs and personnel hazards while providing critical data in areas that were previously too difficult to monitor. This provides a greater downstream benefit for effective water resource management and flood risk reduction in previously data-scarce areas, supporting more resilient communities in the long run.