As we celebrated Water Day yesterday, UNESCO and UN-Water are warning of an impending global water crisis. Therefore, it seemed interesting to us to present you in a little more detail the Swot satellite, one of whose mission is to better understand the water cycle and its impact on climate by focusing on oceanography, hydrology and the coast that never existed did. Commentary by Annick Sylvestre-Baron, Cnes manager of the Swot program and Philippe Maisongrandre, Cnes manager of the Continental Surfaces program.
Launched in December 2022 on board a SpaceX Falcon 9 launch vehicle, the Swot satellite will revolutionize hydrology by carrying an altimeter at an altitude of 891 kilometers, capable of monitoring our planet’s rivers and lakes. Swot will be the first mission to almost completely inventory and monitor the evolution of water resources on the Earth’s surface, improving the understanding of the freshwater cycle and its impact on climate. While Unesco and UN-Water warn of an impending global water crisis for some 3 billion people on earth, this mission is much more necessary and interesting than it seems.
Annick Sylvestre-Baron, Cnes manager of the Swot program, explains to us all the importance of this mission, which will “revolutionize our knowledge of the water cycle on the planet” and why there will be “a before and an after swot”. By focusing on oceanography, continental and coastal hydrology, Swot aims to “improve our knowledge of the hydrological cycle, a cycle intimately linked to climate and its changes.” In fact, it is “the first altimetric imaging mission to observe fresh and salt water levels on the planet” to “nearly completely monitor water supplies in lakes, reservoirs and even wetlands”.
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Understanding the behavior of the continental water cycle
Thus, Swot will complete the range of observations by accurately measuring new parameters essential for monitoring resources, such as “heights, dips that allow the flow of the main rivers to be assessed, a fundamental piece of data that is currently lacking” , says Annick Sylvestre-Baron. From its orbit, Swot will access all water surfaces, including hard-to-reach areas such as the many lakes in Canada or Siberia, which make up a significant portion of the Earth’s freshwater volume, this or blue, which will become more and more sought after.
To understand Swot’s keen interest, Philippe Maisongrandre, Cnes manager of the Continental Surfaces program, reminds us that “Fresh water available in the liquid state accounts for less than 1% of all water on Earth. Therefore, it is important to be able to estimate the availability of this water on the continents and its temporal and spatial development.” However, current altimetric observations “do not cover all continents as regularly”. Swot will correct this bias.
Why is the Swot satellite a revolution?
Combined with other spatial data (optical, thermal, passive microwave, gravimetric, etc.), swot data will allow us to “better understand and know the water cycle on a global scale, as it is currently poorly understood”. You should know that if the total amount of water on Earth has been unchanged and constant for millions of years, “the distribution between the oceans, continental surfaces, and the atmosphere is in constant flux.”
Surprisingly, there is enough water on earth
In absolute terms, “there is enough fresh water on earth, but there is a problem of balancing the needs of the population with the spatio-temporal distribution of the resource”. Certain regions on the continents are affected by the lack of rain, the massive drying out of the soil and the sinking of the groundwater level. In other regions, the rain episodes are intensifying due to the increase in temperature, which increases the precipitating power of the clouds, leading to more frequent floods. For example, in early 2023, some French regions have just experienced consecutive weeks without rain. “Climate change amplifies these phenomena by increasing their frequency and intensity.” Swot will allow to better diagnose and better understand these changes in order to anticipate and better manage them.
“There is enough fresh water on earth, but there is a problem of balancing the needs of the population with the spatio-temporal distribution of the resource”
Swot is therefore timely in the context of population growth and climate change. Its data will help “facilitate water management decisions and will also provide new information about its global cycle.” In fact, measuring the flow of rivers and predicting the water level has a strong application potential in many fields such as “management of drinking water resources, irrigation of crops, river navigation, forecasting of floods and floods, or production of hydroelectric power and nuclear energy (thermoregulated by river water)” , Philippe Maisongrandre would like to tell us.
As a result of major technological innovations, Swot data will therefore not only be of interest to the scientific community. Thanks to the Aval program from which Swot benefited, the data from this satellite will be useful for many concrete applications in everyday life.
Good to know
If you want to know more about the Swot mission, we interviewed Sophie Coutin-Faye, head of altimetry department at Cnes, and Nicolas Picot, Swot downstream project manager, who explain to us why this is an unprecedented, spectacular and scientific one revolution is. We also interviewed Christophe Duplay, Swot program manager for Thales Alenia Space, who built the satellite.