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By NASA
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
Data from the SWOT satellite was used to calculate average water levels for lakes and reservoirs in the Ohio River Basin from July 2023 to November 2024. Yellow indicates values greater than 1,600 feet (500 meters) above sea level; dark purple represents water levels less than 330 feet (100 meters). Data from the U.S.-European Surface Water and Ocean Topography mission gives researchers a detailed look at lakes and reservoirs in a U.S. watershed.
The Ohio River Basin stretches from Pennsylvania to Illinois and contains a system of reservoirs, lakes, and rivers that drains an area almost as large as France. Researchers with the SWOT (Surface Water and Ocean Topography) mission, a collaboration between NASA and the French space agency CNES (Centre National d’Études Spatiales), now have a new tool for measuring water levels not only in this area, which is home to more than 25 million people, but in other watersheds around the world as well.
Since early 2023, SWOT has been measuring the height of nearly all water on Earth’s surface — including oceans, lakes, reservoirs, and rivers — covering nearly the entire globe at least once every 21 days. The SWOT satellite also measures the horizontal extent of water in freshwater bodies. Earlier this year, the mission started making validated data publicly available.
“Having these two perspectives — water extent and levels — at the same time, along with detailed, frequent coverage over large areas, is unprecedented,” said Jida Wang, a hydrologist at the University of Illinois Urbana-Champaign and a member of the SWOT science team. “This is a groundbreaking, exciting aspect of SWOT.”
Researchers can use the mission’s data on water level and extent to calculate how the amount of water stored in a lake or reservoir changes over time. This, in turn, can give hydrologists a more precise picture of river discharge — how much water moves through a particular stretch of river.
The visualization above uses SWOT data from July 2023 to November 2024 to show the average water level above sea level in lakes and reservoirs in the Ohio River Basin, which drains into the Mississippi River. Yellow indicates values greater than 1,600 feet (500 meters), and dark purple represents water levels less than 330 feet (100 meters). Comparing how such levels change can help hydrologists measure water availability over time in a local area or across a watershed.
Complementing a Patchwork of Data
Historically, estimating freshwater availability for communities within a river basin has been challenging. Researchers gather information from gauges installed at certain lakes and reservoirs, from airborne surveys, and from other satellites that look at either water level or extent. But for ground-based and airborne instruments, the coverage can be limited in space and time. Hydrologists can piece together some of what they need from different satellites, but the data may or may not have been taken at the same time, or the researchers might still need to augment the information with measurements from ground-based sensors.
Even then, calculating freshwater availability can be complicated. Much of the work relies on computer models. “Traditional water models often don’t work very well in highly regulated basins like the Ohio because they have trouble representing the unpredictable behavior of dam operations,” said George Allen, a freshwater researcher at Virginia Tech in Blacksburg and a member of the SWOT science team.
Many river basins in the United States include dams and reservoirs managed by a patchwork of entities. While the people who manage a reservoir may know how their section of water behaves, planning for water availability down the entire length of a river can be a challenge. Since SWOT looks at both rivers and lakes, its data can help provide a more unified view.
“The data lets water managers really know what other people in these freshwater systems are doing,” said SWOT science team member Colin Gleason, a hydrologist at the University of Massachusetts Amherst.
While SWOT researchers are excited about the possibilities that the data is opening up, there is still much to be done. The satellite’s high-resolution view of water levels and extent means there is a vast ocean of data that researchers must wade through, and it will take some time to process and analyze the measurements.
More About SWOT
The SWOT satellite was jointly developed by NASA and CNES, with contributions from the Canadian Space Agency (CSA) and the UK Space Agency. NASA’s Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA provided the Ka-band radar interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. The Doppler Orbitography and Radioposition Integrated by Satellite system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground operations were provided by CNES. The KaRIn high-power transmitter assembly was provided by CSA.
To learn more about SWOT, visit:
https://swot.jpl.nasa.gov
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
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Last Updated Dec 17, 2024 Related Terms
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By NASA
4 min read
NASA Satellites Reveal Abrupt Drop in Global Freshwater Levels
Earth (ESD) Earth Home Explore Climate Change Science in Action Multimedia Data For Researchers GRACE satellites measure gravity as they orbit the planet to reveal shifting levels of water on the Earth (artist’s concept). NASA/JPL-Caltech An international team of scientists using observations from NASA-German satellites found evidence that Earth’s total amount of freshwater dropped abruptly starting in May 2014 and has remained low ever since. Reporting in Surveys in Geophysics, the researchers suggested the shift could indicate Earth’s continents have entered a persistently drier phase.
From 2015 through 2023, satellite measurements showed that the average amount of freshwater stored on land — that includes liquid surface water like lakes and rivers, plus water in aquifers underground — was 290 cubic miles (1,200 cubic km) lower than the average levels from 2002 through 2014, said Matthew Rodell, one of the study authors and a hydrologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s two and a half times the volume of Lake Erie lost.”
During times of drought, along with the modern expansion of irrigated agriculture, farms and cities must rely more heavily on groundwater, which can lead to a cycle of declining underground water supplies: freshwater supplies become depleted, rain and snow fail to replenish them, and more groundwater is pumped. The reduction in available water puts a strain on farmers and communities, potentially leading to famine, conflicts, poverty, and an increased risk of disease when people turn to contaminated water sources, according to a UN report on water stress published in 2024.
The team of researchers identified this abrupt, global decrease in freshwater using observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, operated by the German Aerospace Center, German Research Centre for Geosciences, and NASA. GRACE satellites measure fluctuations in Earth’s gravity on monthly scales that reveal changes in the mass of water on and under the ground. The original GRACE satellites flew from March 2002 to October 2017. The successor GRACE–Follow On (GRACE–FO) satellites launched in May 2018.
This map shows the years that terrestrial water storage hit a 22-year minimum (i.e., the land was driest) at each location, based on data from the GRACE and GRACE/FO satellites. A significantly large portion of the global land surface reached this minimum in the nine years since 2015, which happen to be the nine warmest years in the modern temperature record. Image by NASA Earth Observatory/Wanmei Liang with data courtesy of Mary Michael O’Neill The decline in global freshwater reported in the study began with a massive drought in northern and central Brazil, and was followed shortly by a series of major droughts in Australasia, South America, North America, Europe, and Africa. Warmer ocean temperatures in the tropical Pacific from late 2014 into 2016, culminating in one of the most significant El Niño events since 1950, led to shifts in atmospheric jet streams that altered weather and rainfall patterns around the world. However, even after El Niño subsided, global freshwater failed to rebound. In fact, Rodell and team report that 13 of the world’s 30 most intense droughts observed by GRACE occurred since January 2015. Rodell and colleagues suspect that global warming might be contributing to the enduring freshwater depletion.
Global warming leads the atmosphere to hold more water vapor, which results in more extreme precipitation, said NASA Goddard meteorologist Michael Bosilovich. While total annual rain and snowfall levels may not change dramatically, long periods between intense precipitation events allow the soil to dry and become more compact. That decreases the amount of water the ground can absorb when it does rain.
“The problem when you have extreme precipitation,” Bosilovich said, “is the water ends up running off,” instead of soaking in and replenishing groundwater stores. Globally, freshwater levels have stayed consistently low since the 2014-2016 El Niño, while more water remains trapped in the atmosphere as water vapor. “Warming temperatures increase both the evaporation of water from the surface to the atmosphere, and the water-holding capacity of the atmosphere, increasing the frequency and intensity of drought conditions,” he noted.
While there are reasons to suspect that the abrupt drop in freshwater is largely due to global warming, it can be difficult to definitively link the two, said Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech, who was not affiliated with the study. “There are uncertainties in climate predictions,” Werth said. “Measurements and models always come with errors.”
It remains to be seen whether global freshwater will rebound to pre-2015 values, hold steady, or resume its decline. Considering that the nine warmest years in the modern temperature record coincided with the abrupt freshwater decline, Rodell said, “We don’t think this is a coincidence, and it could be a harbinger of what’s to come.”
By James R. Riordon
NASA’s Earth Science News Team
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Last Updated Nov 15, 2024 Editor James Riordon Contact James Riordon james.r.riordon@nasa.gov Location NASA Goddard Space Flight Center Related Terms
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By NASA
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
Clean air is essential for healthy living, but according to the World Health Organization (WHO), almost 99% of the global population breathes air exceeding their guideline limits of air pollution. “Air quality is a measure of how much stuff is in the air, which includes particulates and gaseous pollutants,” said Kristina Pistone, a research scientist at NASA Ames Research Center. Pistone’s research covers both atmospheric and climate areas, with a focus on the effect of atmospheric particles on climate and clouds. “It’s important to understand air quality because it affects your health and how well you can live your life and go about your day,” Pistone said. We sat down with Pistone to learn more about air quality and how it can have a noticeable impact on human health and the environment.
What makes up air quality?
There are six main air pollutants regulated by the Environmental Protection Agency (EPA) in the United States: particulate matter (PM), nitrogen oxides, ozone, sulfur oxides, carbon monoxide, and lead. These pollutants come from from natural sources, such as the particulate matter that rises into the atmosphere from fires and desert dust, or from human activity, such as the ozone generated from sunlight reacting to vehicle emissions.
Satellite image showing wildfire smoke drifting down from Canada into the American Midwest, captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on June 09, 2015. NASA/Jeff Schmaltz
What is the importance of air quality?
Air quality influences health and quality of life. “Just like we need to ingest water, we need to breathe air,” Pistone said. “We have come to expect clean water because we understand that we need it to live and be healthy, and we should expect the same from our air.”
Poor air quality has been tied to cardiovascular and respiratory effects in humans. Short-term exposure to nitrogen dioxide (NO2), for example, can cause respiratory symptoms like coughing and wheezing, and long-term exposure increases the risk of developing respiratory diseases such as asthma or respiratory infections. Exposure to ozone can aggravate the lungs and damage the airways. Exposure to PM2.5 (particulates 2.5 micrometers or smaller) causes lung irritation and has been linked to heart and lung diseases.
In addition to its impacts on human health, poor air quality can damage the environment, polluting bodies of water through acidification and eutrophication. These processes kill plants, deplete soil nutrients, and harm animals.
Measuring Air Quality: the Air Quality Index (AQI)
Air quality is similar to the weather; it can change quickly, even within a matter of hours. To measure and report on air quality, the EPA uses the United States Air Quality Index (AQI). The AQI is calculated by measuring each of the six primary air pollutants on a scale from “Good” to “Hazardous,” to produce a combined AQI numeric value 0-500.
“Usually when we’re talking about air quality, we’re saying that there are things in the atmosphere that we know are not good for humans to be breathing all the time,” Pistone said. “So to have good air quality, you need to be below a certain threshold of pollution.” Localities around the world use different thresholds for “good” air quality, which is often dependent on which pollutants their system measures. In the EPA’s system, an AQI value of 50 or lower is considered good, while 51-100 is considered moderate. An AQI value between 100 and 150 is considered unhealthy for sensitive groups, and higher values are unhealthy to everyone; a health alert is issued when the AQI reaches 200. Any value over 300 is considered hazardous, and is frequently associated with particulate pollution from wildfires.
NASA Air Quality Research and Data Products
Air quality sensors are a valuable resource for capturing air quality data on a local level.
In 2022, the Trace Gas GRoup (TGGR) at NASA Ames Research Center deployed Inexpensive Network Sensor Technology for Exploring Pollution, or INSTEP: a new network of low-cost air quality sensors that measures a variety of pollutants. These sensors are capturing air quality data in certain areas in California, Colorado, and Mongolia, and have proven advantageous for monitoring air quality during California’s fire season.
The 2024 Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) mission integrated sensor data from aircraft, satellites, and ground-based platforms to evaluate air quality over several countries in Asia. The data captured from multiple instruments on these flights, such as the Meteorological Measurement System (MMS) from NASA Ames Atmospheric Science Branch, are used to refine air quality models to forecast and assess air quality conditions.
Agency-wide, NASA has a range of Earth-observing satellites and other technology to capture and report air quality data. In 2023, NASA launched the Tropospheric Emissions: Monitoring of Pollution (TEMPO) mission, which measures air quality and pollution over North America. NASA’s Land, Atmosphere Near real-time Capability for Earth Observations (LANCE) tool provides air quality forecasters with measurements compiled from a multitude of NASA instruments, within three hours of its observation.
Nitrogen dioxide levels over the D.C./Philadelphia/New York City region measured by TEMPO.NASA/Scientific Visualization Studio
Air Quality Resources to Learn More
In addition to the EPA’s website, which houses air-quality related sources, the EPA also has a platform called AirNow, which reports the local AQI across the United States and allows users to check air quality levels in their area. Pistone also recommends looking at Purple Air’s real-time map, which displays PM data taken from a crowd-sourced network of low-cost sensors and translates those measurements to estimate AQI. For those concerned about air quality, Pistone recommends checking out https://cleanaircrew.org/ for resources on indoor air quality, breathing safely with wildfire smoke, and even building your own box fan filter.
To learn more about air quality research applications, see NASA’s Applied Sciences Program’s Health & Air Quality program area, which details the use of Earth observations to assess and address air quality concerns at local, regional, and national levels. Additionally, the NASA Health and Air Quality Applied Sciences Team (HAQAST) helps connect NASA data and tools with stakeholders to better share and understand the effects of air quality on human health.
Written by Katera Lee, NASA Ames Research Center
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Last Updated Oct 18, 2024 Related Terms
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