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  • ✇Eos
  • Temperatures in Nearly All Major U.S. Cities Have Warmed Since First Earth Day Grace van Deelen
    Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today. After more than half a century of Earth Days, one planetary challenge—climate change—threatens our planet more than ever. In 1970, the year Sen. Gaylord Nelson (D-Wisc.) organized the first Earth Day events, the annual average concentration of carbon dioxide in the atmosphere was 326 parts per million. In 2025, it was 31% higher, at 427 parts p
     

Temperatures in Nearly All Major U.S. Cities Have Warmed Since First Earth Day

22 April 2026 at 18:37
A map of the United States shows which states have warmed the most since 1970. Alaska, New Jersey, New Mexico, Delaware, Massachusetts, and Vermont are the six fastest-warming states.

Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

After more than half a century of Earth Days, one planetary challenge—climate change—threatens our planet more than ever.

In 1970, the year Sen. Gaylord Nelson (D-Wisc.) organized the first Earth Day events, the annual average concentration of carbon dioxide in the atmosphere was 326 parts per million. In 2025, it was 31% higher, at 427 parts per million. 

“It may sound small, but it’s reshaping daily life.”

Changes in average annual temperatures in U.S. cities and states show the powerful effects of this increase in heat-trapping carbon dioxide. A new analysis, published today by climate research and communications nonprofit Climate Central, found that since 1970, all 50 states and 99% of major U.S. cities have warmed, with an average city-level increase of 1.6°C (2.9°F).

“It may sound small, but it’s reshaping daily life,” Shel Winkley, a meteorologist at Climate Central, said in a video released alongside the report. 

On average, the 49 U.S. states analyzed in the report have warmed by 1.7°C (3.0°F) since 1970. The six states that have warmed the fastest since the first Earth Day are Alaska with a 2.4°C (4.4°F) increase, New Jersey and New Mexico with a 2.1°C (3.7°F) increase, and Delaware, Massachusetts, and Vermont with a 2°C (3.6°F). Trends for Hawaii, which were analyzed separately and not included in the national average, also showed statewide warming.

In 2025, the United States was on average 1.4°C (2.6°F) warmer than the 20th century average. The Paris Agreement, a legally binding global treaty, sets a goal to limit warming to 1.5°C (2.7°F) above preindustrial levels, though some scientists expect that the world has already entered the period of time during which this limit will be breached.

A graph shows how much Reno, Nevada, and the United States have warmed since 1970. Reno has warmed 7.9 degrees Fahrenheit, Nevada has warmed 3 degrees, and the United States has warmed 2.9 degrees.
Warming is occurring much faster in some cities than in their respective states, or than the United States as a whole. Check out your city’s data in the Climate Central report. Credit: Climate Central, CC BY 4.0

Warming trends in the United States are most pronounced in the Southwest, where cities have warmed an average of 1.9°C (3.5°F) since 1970. And in some cases, cities are warming much faster than whole states. Three of the five cities that have warmed the fastest since 1970 are in the Southwest: Reno, Nev., with an increase of 4.4°C (7.9°F), Las Vegas, with an increase of 3.3°C (6.0°F), and El Paso, Texas, with an increase of 3.3°C (5.9°F). 

The effects are evident at the national, state, and local levels. Temperatures have warmed in 240 of the 242 cities analyzed by Climate Central. Harrisonburg, VA and Monterey, CA were the only two cities analyzed that have not warmed since 1970.

The report highlights some good Earth Day news, however, and points out that solar and wind power generation is at an all-time high in the United States, accounting for 19% of the electricity generated in the country in 2025 despite those industries facing recent headwinds from the federal administration. 

“Every fraction of a degree [of warming] that we prevent does matter, for our health, for our communities, and for the world that we’re passing on to the next generations,” Winkley said. 

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org.

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  • Location, Location, Location: The “Where” of Reforestation May Matter More Than the Extent Faith Ishii
    Planting more trees will decelerate climate change only if those trees are placed in optimal locations—primarily the tropics and subtropics—suggests new research published in Communications Earth and Environment. However, planting trees in locations like Alaska, Siberia, and large parts of the United States could actually lead to warming, said lead author and doctoral student at ETH Zurich Nora Fahrenbach. Much of the current thinking in nature-based solutions, Fahrenbach said, is ba
     

Location, Location, Location: The “Where” of Reforestation May Matter More Than the Extent

22 April 2026 at 12:36
A forest at golden hour

Planting more trees will decelerate climate change only if those trees are placed in optimal locations—primarily the tropics and subtropics—suggests new research published in Communications Earth and Environment. However, planting trees in locations like Alaska, Siberia, and large parts of the United States could actually lead to warming, said lead author and doctoral student at ETH Zurich Nora Fahrenbach.

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Much of the current thinking in nature-based solutions, Fahrenbach said, is based on the idea that “more is better.”

As in, “we’ll plant a trillion trees, or we’ll plant more than a trillion trees, and we are going to get more cooling, right?” Fahrenbach said. “That’s something we show is just not the case.”

Fahrenbach researches reforestation potentials, or global maps that identify areas where trees could be planted to mitigate climate change. In this work, she and her colleagues compared three prominent reforestation potentials to determine the effect of tree placement on local and global temperatures.

One scenario involved reforesting about 926 million hectares focused mostly on the tropics and resulted in about 0.25°C of cooling by 2100. Another called for reforesting 894 million hectares, including large areas in northern temperate and polar latitudes, and resulted in 0.13°C of cooling by 2100.

The third scenario involved planting forests strategically over only 440 million hectares of mostly tropical and subtropical land (less than half of the area covered in the other scenarios) but also resulted in 0.13°C of cooling. Geography, the findings suggest, may matter more than quantity when it comes to the cooling benefits of reforestation efforts.

Let’s Get (Biogeo)physical

The researchers modeled all three scenarios using the same parameters: Trees were planted from 2015 to 2070 and then remained steady in their population until 2100.

Planting trees in one area doesn’t just change the local temperature but has effects across the world.

All three models identified reforestation opportunities in regions such as the eastern United States, Amazonia, the Congo rainforest, and eastern China, as well as regions for which reforestation would not be as impactful, such as polar regions in the Northern Hemisphere. The researchers also found significant temperature changes across the Atlantic and Indian oceans as a result of atmospheric changes induced by reforestation, demonstrating an interconnected reality: Planting trees in one area doesn’t just change the local temperature but has effects across the world.

These local and nonlocal effects can be explained by a combination of biogeochemical and biogeophysical effects.

A biogeochemical effect relates to the movement of chemicals or chemical elements, such as trees absorbing carbon from the atmosphere.

A biogeophysical effect relates to the physical results of changing the land’s surface: Placing a tree in a snowy region, for instance, decreases the land’s albedo, meaning it causes the land surface to become darker and absorb more light, leading to more local heat. This rise in surface temperature also raises air temperature, creating cascading effects on wind patterns and oceanic currents.

Considering both processes together is essential for understanding whether a net cooling or net heating effect exists, but most policies focus only on biogeochemical effects, seeing trees solely for their ability to absorb carbon from the atmosphere, Fahrenbach said. They include prominent international policies such as the Paris Agreement and the United Nations’ Framework for REDD+.

“Really, we would also need to consider the biogeophysical effects,” Fahrenbach said. “That’s harder to do, right, considering those nonlocal effects, because just imagine, some country is going to plant a lot of trees, and that’s going to lead to warming somewhere else.”

A Call to Policymakers

Emilio Vilanova, a forest ecologist at the climate action nonprofit Verra, wrote by email, “The most important message for me is that this study emphasizes something that is often not well addressed in reforestation projects: Reforestation is not just about planting trees—it’s about designing where new forests go to maximize benefits and avoid unintended consequences.”

“Reforestation is a helpful tool, not a stand-alone solution to climate change.”

Vilanova also said the study puts the potential for reforestation efforts to address climate change in perspective. “Even very large reforestation efforts would only reduce global temperatures by about 0.13–0.25°C by the end of the century,” he said. “While meaningful, this finding also reinforces that reforestation is a helpful tool, not a stand-alone solution to climate change.”

Though the limited potential for change is sobering, the authors and Vilanova pointed out that this change does matter and that it matters how we think of our approach. They advocate for policies that adopt reforestation strategies based on location and that acknowledge both the local and nonlocal effects of reforestation.

“We really need to make sure that where we plant first, it has benefits locally, it has benefits globally,” Fahrenbach said.

—Andrew Meissen (@AndrewMeissen), Science Writer

22 April 2026: This article was updated to correct Nora Fahrenbach’s position at ETH Zurich.

This news article is included in our ENGAGE resource for educators seeking science news for their classroom lessons. Browse all ENGAGE articles, and share with your fellow educators how you integrated the article into an activity in the comments section below.

Citation: Meissen, A. (2026), Location, location, location: The “where” of reforestation may matter more than the extent, Eos, 107, https://doi.org/10.1029/2026EO260125. Published on 22 April 2026.
Text © 2026. The authors. CC BY-NC-ND 3.0
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  • ✇Eos
  • More Braided Rivers from Increasing Flow Variability Chris Micucci
    Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances The evolution of rivers that split into multiple channels is a scientific challenge in terms of modeling and prediction. On the other hand, these rivers are widespread and play a key role for ecosystems’ life, groundwater recharge, and therefore, water security. They are also extremely sensitive to hydroclimatic changes, leading to shifts in precipitation, erosion and sediment transport. Z
     

More Braided Rivers from Increasing Flow Variability

22 April 2026 at 12:00
Photo of a braided river.
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

The evolution of rivers that split into multiple channels is a scientific challenge in terms of modeling and prediction. On the other hand, these rivers are widespread and play a key role for ecosystems’ life, groundwater recharge, and therefore, water security. They are also extremely sensitive to hydroclimatic changes, leading to shifts in precipitation, erosion and sediment transport.

Zhao et al. [2026] investigate the drivers of river evolution for 97 multithread river reaches worldwide, spanning diverse climates and morphologies. The study reveals the key role of intermittency for river evolution. In particular, higher flow intermittency could lead to more even flow partitioning among threads, therefore impacting hydrology and ecosystems. With flow variability increasing after climate change, rivers are likely to increase their thread count, thus impacting livelihoods and ecosystems.

Two example multithread reaches shown in Landsat images from (b) the Irtysh River (wandering) and (c) the Yukon River (braided). Credit: Zhao et al. [2026], Figure 1(b,c)

Citation: Zhao, F., Ganti, V., Chadwick, A., Greenberg, E., McLeod, J., Liu, Y., et al. (2026). Global hydroclimatic controls on multithread River dynamics. AGU Advances, 7, e2025AV002166. https://doi.org/10.1029/2025AV002166

—Alberto Montanari, Editor-in-Chief, AGU Advances

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Text © 2026. The authors. CC BY-NC-ND 3.0
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  • ✇Eos
  • What’s Below the Great Salt Lake? More Water Anaise Aristide
    Since 1989, Utah’s Great Salt Lake has lost some 70% of its surface area, reducing its ecosystem services and creating stretches of drying lake bed (playa) that send toxic dust into the air. That drying ground has also provided opportunities for scientists to survey what lies below the lake’s floor. In a study published in Geosciences, researchers revealed glimpses of fresh water and salt water, with some fresh water lurking only a few meters below the surface. The work could provide clues f
     

What’s Below the Great Salt Lake? More Water

21 April 2026 at 12:44
Researchers stand in the distance as an orange electrical cord snakes across a dry lake bed in the Great Salt Lake.

Since 1989, Utah’s Great Salt Lake has lost some 70% of its surface area, reducing its ecosystem services and creating stretches of drying lake bed (playa) that send toxic dust into the air.

That drying ground has also provided opportunities for scientists to survey what lies below the lake’s floor. In a study published in Geosciences, researchers revealed glimpses of fresh water and salt water, with some fresh water lurking only a few meters below the surface. The work could provide clues for conserving the lake, a crucial resource for both the ecology and the economy of the region.

Salt Lake, Fresh Water

In 2023, Michael Thorne and colleagues began using a technique known as electrical resistivity tomography (ERT), which can reveal the presence of fresh or salty water, at dozens of spots near the southern and eastern edges of the Great Salt Lake. Thorne is a geophysicist at the University of Utah in Salt Lake City and a coauthor of the new study.

The lake’s desiccation allowed the researchers to access areas where “at previous times, you would never be able to do measurements because [they] would be underwater,” said Thorne.

Establishing a network of ERT sensors requires robust fieldwork. Over the course of long days in the field, Mason Jacketta, lead author of the new study, and others placed electrodes into the ground a few meters apart, making lines that stretched hundreds of meters. Between pairs of electrodes, they measured the resistance to electrical current. Salty water, filled with electricity-conducting ions, has lower resistance than fresh water.

Paired with information on the rock and sediment beneath the surface, as well as with measurements from nearby wells, the ERT data allowed the team to work out a profile of how electrical resistance varied with depth and to figure out what kind of water seeped through pores in the ground below. The team shared the results of their work on the southern part of the lake in Geosciences, while more in-depth findings about the eastern shore will appear in an upcoming publication.

“What this is really showing is that [fresh water is] prevalent all over the place.”

At many of the sites, Jacketta and others found fresh water near the surface.

“What this is really showing is that [fresh water is] prevalent all over the place,” said Elliot Jagniecki, a geologist at the Utah Geological Survey who wasn’t part of the work.

That fresh water was often in close proximity to patches of salty groundwater. At one spot in the southeastern part of the lake, the team found a shallow layer of brine. But right below that, at only 5 meters of depth, they encountered fresh water. At the team’s most northern study site, they found fresh water around 2 meters deep. On the southern shore, they found fresh water in some places as shallow as 2.8 meters.

Mysterious Formations

The team’s results also helped explain curious features around the Great Salt Lake, including mounds made of salt and islands made of reeds.

The lacy-looking layers of the lake’s so-called mirabilite mounds form in the winter, when the cold freezes upwelling salty water, concentrating its salts. With measurements taken next to where some mirabilite mounds form, the researchers could visualize the underground conduits that send salty water to the surface.

While mirabilite mounds form close to shore, mounds made of Phragmites reeds appear in the lake’s interior as well as along its periphery. Thorne and his colleague William Johnson first noticed these mysterious circles popping up in Google Maps more than a decade ago. When they went to investigate, they found Phragmites.

“The population of Phragmites around the Great Salt Lake is really not allowing fresh groundwater to go back into the Great Salt Lake.”

In the new work, the team placed a line for electrical resistivity tomography straight through a Phragmites mound. These reeds wouldn’t be able to survive in the lake’s briny water, Thorne said, but the team’s results showed fresh water rising right to where the invasive reeds grew thick.

“The population of Phragmites around the Great Salt Lake is really not allowing fresh groundwater to go back into the Great Salt Lake,” said study coauthor Tonie van Dam, a geophysicist at the University of Utah. The reeds suck up some 70,000 acre-feet of fresh water that could go back into the lake, she said. In “sucking up [fresh water] for their own existence,” van Dam explained, the reeds crowd out native plant species that provide habitat for native birds.

More Than a Beautiful Landscape

Overall, the study provides a new picture of the fresh and salty groundwater beneath the lake and how these resources feed what people observe at the surface.

It’s also helped to prompt other work, Thorne said, including one recent study in which researchers used a helicopter carrying a wire loop to create and sense electrical currents underground. That study, published in Scientific Reports, suggested there could be a large amount of fresh water under one part of the lake.

But that work is a proof of concept, Jagniecki said, and accessing such potential aquifers might not be sufficient to help address the lake’s current desiccation. Even if they could, refilling them could take thousands of years. “I just don’t think that’s a solution,” he said.

Saline lakes are fragile ecosystems sensitive to climate change, Jagniecki said. The Great Salt Lake harbors plenty of life, such as brine shrimp that become food for a host of migratory birds that use the lake as a stopover. Mineral extraction and the use of brine shrimp for feed in aquaculture are important drivers of Utah’s economy.

Getting a better understanding of how saline lake systems function could be helpful in conserving them and maintaining the resources they provide humans, Jagniecki explained.

“It’s actually more than that. It’s a beautiful landscape,” he said.

—Carolyn Wilke, Science Writer

Citation: Wilke, C. (2026), What’s below the Great Salt Lake? More water, Eos, 107, https://doi.org/10.1029/2026EO260127. Published on 21 April 2026.
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  • ✇Eos
  • 通往真正可持续太空供水系统的路径 Faith Ishii
    Source: Water Resources Research This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。 如果人类想要在太空生活,无论是在航天器里还是在火星上,首先要解决的一个问题就是如何获取水,来满足饮用、卫生需求以及为维持生命所需的植物提供水分。即便只是将水运送到近地轨道上的国际空间站(ISS),也需要花费数万美元。因此,找到在太空中高效、持久且可靠地获取和再利用水资源的方法,对于长期在太空居住至关重要。 目前的系统,比如国际空间站上的环境控制与生命支持系统(ECLSS),为闭合式水回收提供了蓝图,但它们还需要改进才能适应未来的应用。与此同时,近期的技术和科学进步正为在严苛环境下寻找、净化和管理水资源开辟新的途径。在一篇新的综述中,Olawade等人概述了地外水资源管理的现状,以及该领域的前景和挑战。 作者指出,太空水系统需要具备闭环、高效和持久耐用的特性,同时还要满足低能耗的要求。目前,ECLSS能耗过高,其效率可能也不足以满足长期任务的需求。未来建议采用的过
     

通往真正可持续太空供水系统的路径

21 April 2026 at 12:39
国际空间站上的宇航员Kayla Barron将一个银色的金属圆筒(大小和汽水罐差不多)举到镜头前。
Source: Water Resources Research

This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。

如果人类想要在太空生活,无论是在航天器里还是在火星上,首先要解决的一个问题就是如何获取水,来满足饮用、卫生需求以及为维持生命所需的植物提供水分。即便只是将水运送到近地轨道上的国际空间站(ISS),也需要花费数万美元。因此,找到在太空中高效、持久且可靠地获取和再利用水资源的方法,对于长期在太空居住至关重要。

目前的系统,比如国际空间站上的环境控制与生命支持系统(ECLSS),为闭合式水回收提供了蓝图,但它们还需要改进才能适应未来的应用。与此同时,近期的技术和科学进步正为在严苛环境下寻找、净化和管理水资源开辟新的途径。在一篇新的综述中,Olawade等人概述了地外水资源管理的现状,以及该领域的前景和挑战。

作者指出,太空水系统需要具备闭环、高效和持久耐用的特性,同时还要满足低能耗的要求。目前,ECLSS能耗过高,其效率可能也不足以满足长期任务的需求。未来建议采用的过滤和回收方法包括:利用光催化技术通过光线净化水,利用生物反应器过滤尿液和废水,利用离子交换系统去除提取水中的溶解盐和重金属,以及利用紫外线臭氧消毒杀灭病原体。每种方法各有优缺点:例如,生物反应器中的微生物燃料电池可以发电,而光催化净化则能耗较低。

在月球或火星这样的地方获取水,要么需要从风化层中提取水,要么需要钻探冰体。如何为水回收系统提供足够的能源也是一个问题,因此开发节能系统是需要优先考虑的事项。水系统的耐久性也很重要,既要保护宇航员的安全,又要能减少繁重的维护工作。

新兴技术有望应对其中许多挑战。作者们指出两个具有巨大应用前景的领域,一是纳米技术的发展,它可用于制造定制化程度更高、过滤效果更佳且耐污染的膜材料,二是人工智能(AI)技术在水系统自主管理中的应用。(Water Resources Research, https://doi.org/10.1029/2025WR041273, 2026)

—科学撰稿人Nathaniel Scharping (@nathanielscharp)

This translation was made by Wiley. 本文翻译由Wiley提供。

Read this article on WeChat. 在微信上阅读本文。

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  • ✇Eos
  • Weather Radar Data Reveal the Dynamics of Rapidly Spreading Wildfires William J. Randel
    Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Atmospheres The 2018 Camp Fire was the deadliest and most destructive wildfire in California history. The Camp Fire spread extremely rapidly, driven by strong winds and dry fuels, but also by organized long-range spotting, i.e. lofting and downwind fallout of burning embers to ignite new fires. Using operational Doppler radar and satellite observations, Lareau [2026] pr
     

Weather Radar Data Reveal the Dynamics of Rapidly Spreading Wildfires

21 April 2026 at 12:00
Aerial photo of smoke billowing from a wildfire.
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Atmospheres

The 2018 Camp Fire was the deadliest and most destructive wildfire in California history. The Camp Fire spread extremely rapidly, driven by strong winds and dry fuels, but also by organized long-range spotting, i.e. lofting and downwind fallout of burning embers to ignite new fires.

Using operational Doppler radar and satellite observations, Lareau [2026] provides the first high resolution depiction of spotting behavior during an extreme wildfire. Observations show that spot fire events for the Camp Fire occurred 5-10 kilometers ahead of the fire front, quickly merging into new fire lines. Spot fires are not random but aligned within coherent fallout zones that are shaped by plume dynamics and background winds. These results show that operational weather radar can identify lofting and fallout regions in real time, providing a new way to anticipate spotting-driven fire spread and improve early warnings for fast-moving wildfires.

(a) Along wind cross section of Camp Fire plume reflectivity observed by radar measurements, showing distinct updrafts (white arrows) and ashfall regions (blue dashed arrow). Spot fires within 10 minutes of these radar measurements are shown as filled cyan triangles. (b) Map of column maximum radar reflectivity and fire perimeter. In both panels the black dashed line indicates the eastern edge of the town of Paradise, California. Credit: Lareau [2026], Figure 6ab

Citation: Lareau, N. P. (2026). Plume-coupled long-range spotting drove the explosive spread of the 2018 Camp Fire. Journal of Geophysical Research: Atmospheres, 131, e2025JD045798. https://doi.org/10.1029/2025JD045798

—William Randel, Editor, JGR: Atmospheres

The logo for the United Nations Sustainable Development Goal 13 is at left. To its right is the following text: The research reported here supports Sustainable Development Goal 13. AGU is committed to supporting the United Nations 2030 Agenda for Sustainable Development, which provides a shared blueprint for peace and prosperity for people and the planet, now and into the future.
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  • ✇Eos
  • Can Any Single Satellite Keep Up with the World’s Floods? Chloe Campo
    Editors’ Vox is a blog from AGU’s Publications Department. As climate change increases the frequency and intensity of flooding, it’s becoming increasingly important to monitor and predict flood hazards at different scales. A new article in Reviews of Geophysics presents a data-driven performance analysis of various space-based sensors that monitor flood hazards. Here, we asked the lead author to give an overview of satellite-based flood monitoring, the benefits and challenges of using satell
     

Can Any Single Satellite Keep Up with the World’s Floods?

20 April 2026 at 13:32
Satellite image of a river with highlights indicating flood areas.
Editors’ Vox is a blog from AGU’s Publications Department.

As climate change increases the frequency and intensity of flooding, it’s becoming increasingly important to monitor and predict flood hazards at different scales. A new article in Reviews of Geophysics presents a data-driven performance analysis of various space-based sensors that monitor flood hazards. Here, we asked the lead author to give an overview of satellite-based flood monitoring, the benefits and challenges of using satellite-based sensors, and future space-based projects.

Why is it important to monitor the surface waters on Earth? 

More than half of the world’s population lives within three kilometers of a freshwater body. When seasonal flooding behaves as anticipated, it provides essential nutrient replenishment to soils and crops. However, extreme flooding disturbs the careful balance of freshwater systems and can cause damaging flooding that disrupts livelihoods.

Climate change is making these extremes more frequent and less predictable, while expanding populations in flood-prone areas amplify the human cost. Continuous monitoring of Earth’s surface waters is essential as it helps us anticipate hazards, evaluate risk, and design interventions that protect the people and places most exposed to hydrologic hazards.

What are the benefits of monitoring flood inundation from space compared to other techniques? 

Monitoring flood inundation from space is advantageous due to the wide-scale global coverage that captures important information over large areas. In-situ sensors, such as river gauges, provide valuable data but are limited in spatial coverage and may even fail under significant flood conditions. A single satellite overpass can potentially capture an entire river basin, allowing responders to see where water has spread, which communities are affected, and how the event is evolving.

When did scientists first start using satellites to monitor surface waters?

The value of monitoring surface water from space was first realized in the early 1970s, following the launch of Landsat 1. Soon after launch, it captured imagery of the devastating 1973 Mississippi River floods, producing one of the first flood maps made from space (Figure 1).  By the early 2000s, NASA’s MODIS sensors were providing global coverage at a daily frequency. Today, multiple global flood monitoring systems are in place, including the European Union’s Copernicus Emergency Management Service, which maps floods using Sentinel-1 synthetic aperture radar (SAR), and NOAA’s VIIRS Flood Mapping system.

Figure 1. Imagery from the start of the Landsat 1 mission illustrating the extent of the Mississippi River flooding of 1973 (EROS History Project). The Earth Resources Technology Satellite 1 (ERTS-1) was renamed Landsat 1 in 1975. Credit: USGS

What are the three types of satellite-based sensors that your review focuses on? 

Our review examines three families. Multispectral (optical and thermal) sensors capture reflected sunlight or emitted heat. Microwave sensors, including SAR, passive microwave radiometers, and GNSS Reflectometry (GNSS-R), can observe through clouds and at night but involve trade-offs between resolution and coverage. Finally, altimetric sensors measure water surface elevation with high precision but only along narrow tracks. Each family has distinct strengths and weaknesses that lend themselves to use in combination for comprehensive flood inundation monitoring.

What are some of the challenges of using satellite-based sensors to monitor flooding?

The fundamental problem is that floods and satellite observations are mismatched in time and space. Optical sensors often capture clouds rather than the floodwater beneath. Cloud-penetrating sensors like SAR can miss flood peaks if their orbital schedule doesn’t align with the event, and dense vegetation can obstruct floodwater from both optical and shorter-wavelength radar. Sensors with high temporal resolution typically deliver data at coarse spatial resolutions, sometimes tens of kilometers per pixel. These trade-offs form what we describe as the “iron triangle” of Earth observation: temporal resolution, spatial resolution, and cost. A sensor can typically be optimized for two, but rarely all three. Occasionally, the timing and conditions of a flood align well with sensors whose strengths are complementary across the iron triangle, yielding the kind of multi-sensor view shown in Figure 2.

Figure 2. Sentinel‐2 MSI True Color Image with Sentinel‐1 SAR derived flood‐extent superimposed on top. The top right circle highlights the missing SAR‐derived information, whereas the bottom circle highlights the missing optical information. Credit: Campo et al. [2026], Figure 5

What are some upcoming space-based sensor projects that could advance the field of hydrology?

Several are already reshaping the field. NISAR, a joint NASA–ISRO radar satellite launched in 2025, carries an L-band sensor designed to penetrate vegetation canopy, providing new insights into flooding beneath vegetation. Sentinel-1D, launched in late 2025, has restored the Sentinel-1 constellation to full two-satellite capacity, halving the revisit time. Landsat Next, a planned three-satellite constellation with 26 spectral bands and a six-day revisit, would provide valuable hydrologic data at both high temporal and spectral resolutions. However, recent budget pressures have introduced uncertainty about its final scope. Finally, the HydroGNSS mission from ESA will use GNSS-R to monitor hydrologically linked Essential Climate Variables.

—Chloe Campo (S4088633@student.rmit.edu.au; 0009-0007-4259-300X), Royal Melbourne Institute of Technology University: Melbourne, Australia

The logo for the United Nations Sustainable Development Goal 13 is at left. To its right is the following text: The research reported here supports Sustainable Development Goal 13. AGU is committed to supporting the United Nations 2030 Agenda for Sustainable Development, which provides a shared blueprint for peace and prosperity for people and the planet, now and into the future.

Editor’s Note: It is the policy of AGU Publications to invite the authors of articles published in Reviews of Geophysics to write a summary for Eos Editors’ Vox.

Citation: Campo, C. (2026), Can any single satellite keep up with the world’s floods?, Eos, 107, https://doi.org/10.1029/2026EO265016. Published on 20 April 2026.
This article does not represent the opinion of AGU, Eos, or any of its affiliates. It is solely the opinion of the author(s).
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  • What Makes Mars’s Magnetotail Flap? Sarah Stanley
    Source: AGU Advances The Sun continuously blasts charged, magnetic field–carrying particles, or plasma, in all directions. This solar wind interacts with the magnetic fields and atmospheres of several of our solar system’s planets and other bodies, sculpting long magnetic tails of charged particles—magnetotails—that stretch into space behind them. Magnetotails contain thin layers of electric current–carrying plasma sheets, which sometimes “flap” in an up-and-down waving motion. Spacecraft
     

What Makes Mars’s Magnetotail Flap?

20 April 2026 at 13:08
A large, round, glowing yellow shape is shown at right (the Sun), and a smaller, reddish-brown sphere is at left (Mars). Pale yellow streaks and thicker curving white lines radiate from the Sun in all directions. Mars appears to disrupt the flow of the pale yellow streaks, which deflect around it like water flowing around a pebble in a stream.
Source: AGU Advances

The Sun continuously blasts charged, magnetic field–carrying particles, or plasma, in all directions. This solar wind interacts with the magnetic fields and atmospheres of several of our solar system’s planets and other bodies, sculpting long magnetic tails of charged particles—magnetotails—that stretch into space behind them.

Magnetotails contain thin layers of electric current–carrying plasma sheets, which sometimes “flap” in an up-and-down waving motion. Spacecraft observations have revealed that flapping in Earth’s magnetotail can be driven by a process called magnetic reconnection, in which magnetic field lines rapidly break and then snap together in a new configuration, releasing stored energy. However, whether reconnection plays this same role beyond Earth has thus far been a mystery.

Wen et al. report the first evidence that magnetic reconnection may also trigger magnetotail flapping at Mars.

Unlike Earth, Mars lost its global magnetic field billions of years ago. But it still sports a magnetotail, thanks in large part to interactions between the solar wind and charged particles in its upper atmosphere. Strong magnetic fields embedded in certain patches of the Martian crust—remnants of its lost planet-wide field—also influence the magnetotail.

Until recently, Mars’s magnetotail could only be studied using observations from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. MAVEN showed that the Martian magnetotail is highly dynamic, with a structure that twists, shifts, and flaps—and from which charged particles may escape into space. But because MAVEN can observe only one part of the magnetotail at a time, it couldn’t identify what processes might trigger flapping.

Another spacecraft, China’s Tianwen-1 orbiter, has now provided a second set of eyes. The researchers analyzed simultaneous observations from the two spacecraft, finding that signatures of magnetic reconnection detected by MAVEN in the upstream part of the magnetotail tended to coincide with flapping events detected downstream by Tianwen-1.

Before or during flapping, the spacecraft also detected temporary, twisted plasma structures known as flux ropes. A similar link has previously been observed on Earth, and it suggests that flux ropes generated by magnetic reconnection upstream might propagate downstream, driving instabilities in the magnetotail’s plasma sheets and triggering flapping.

Though more research is needed to confirm these findings, they shed new light on how energy moves and is released in space around Mars—and possibly other planets and celestial objects. (AGU Advances, https://doi.org/10.1029/2026AV002343, 2026)

—Sarah Stanley, Science Writer

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Citation: Stanley, S. (2026), What makes Mars’s magnetotail flap?, Eos, 107, https://doi.org/10.1029/2026EO260123. Published on 20 April 2026.
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  • Choice of Glen’s n Leads to Differing Projections of Ice Sheet Mass Loss Ann Rowan
    Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Earth Surface Glacier ice is a crystalline material that flows across the Earth’s surface and is often close to the pressure-melting point. The way ice deforms is therefore an interplay of many factors including the temperature, grain size, and purity of the ice. Numerical models of ice flow are based on the Glen-Nye flow law (Glen’s Law)—a simple relationship between stre
     

Choice of Glen’s n Leads to Differing Projections of Ice Sheet Mass Loss

20 April 2026 at 12:00
Photo of a glacier with mountains in the background.
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Earth Surface

Glacier ice is a crystalline material that flows across the Earth’s surface and is often close to the pressure-melting point. The way ice deforms is therefore an interplay of many factors including the temperature, grain size, and purity of the ice. Numerical models of ice flow are based on the Glen-Nye flow law (Glen’s Law)—a simple relationship between stress and strain in ice developed by John Glen and John Nye from laboratory experiments in the 1950s. Glen’s Law derives strain (creep, or deformation flow of ice) from the applied stress raised to the power of the exponent n, multiplied by the temperature-dependent constant A. The values for these parameters are empirical, and both linear and power-law forms of Glen’s Law have been proposed, although a value of 3 is typically used for n.

Lilien et al. [2026] use a flowline model to explore the impact of the choice of value for Glen’s n on the outcome of projections of ice sheet mass change, considering different values for A and different glacier sliding laws. They found that the relationship between n and glacier mass loss is complicated and varies depending on glacier type. For dynamically controlled glaciers, increasing n increased mass loss, as ice flowed more rapidly into ablation areas. For surface mass balance-controlled glaciers, increasing n decreased mass loss, because ice flux decreased at the equilibrium line. The authors find that using a single value for Glen’s n is likely to lead to large uncertainties in projections of ice sheet change, and therefore studies of future ice sheet mass loss need to consider how the flow-law exponent varies spatially.

Citation: Lilien, D. A., Ranganathan, M., & Shapero, D. R. (2026). Effect of the flow-law exponent on ice-stream sensitivity to melt. Journal of Geophysical Research: Earth Surface,131, e2025JF008726. https://doi.org/10.1029/2025JF008726  

—Ann Rowan, Editor-in-Chief, JGR: Earth Surface

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  • Hundreds of Candidates Put the “Science” in “Political Science” Emily Gardner
    Research & Developments is a blog for brief updates that provide context for the flurry of news regarding law and policy changes that impact science and scientists today. More U.S. scientists are running for state and federal office in the U.S. midterm elections than ever before, Nature reports. Scientist-candidates represent an array of parties, although most profiled in Nature identify as Democrats. 314 Action, an organization focused on getting Democrats with scientific backgro
     

Hundreds of Candidates Put the “Science” in “Political Science”

17 April 2026 at 18:03
The U.S. capitol building seen at night.

Research & Developments is a blog for brief updates that provide context for the flurry of news regarding law and policy changes that impact science and scientists today.

More U.S. scientists are running for state and federal office in the U.S. midterm elections than ever before, Nature reports. Scientist-candidates represent an array of parties, although most profiled in Nature identify as Democrats.

314 Action, an organization focused on getting Democrats with scientific backgrounds elected to public office, offers financial support and training to candidates who apply for it. This year, the organization told Nature, they’ve received nearly three times as many applications as usual.

Sam Wang, a neuroscientist at Princeton and director of the Princeton Gerrymandering Project, is running to represent New Jersey’s 12th Congressional District.

“Usually, scientists stick with a specialized field,” Wang, a Democrat, wrote in an opinion for The Daily Princetonian. “However, I am deeply unhappy with how unequally power is divided in our society. So I have used my statistical abilities to level one part of democracy’s playing field: by repairing unfair elections.”

Why Now?

This year, Democratic candidates appear to be motivated by cuts to federal science programs, grants, and agencies, Nature reports, while Republican candidates like Jeff Wilson, who is running to represent the 13th district of Illinois, cite the pursuit of energy independence.  Third-party scientist-candidates have also run, and scientists are entering local and municipal arenas, too.

Specifically, with the recent repeal of the Endangerment Finding, loosened restrictions on pollution, and plans to break up the National Center for Atmospheric Research, some candidates and their supporters think science needs a more prominent position in public policy.

The rise in scientist candidates may also be part of an ongoing trend. More than 200 STEM professionals ran for office in the 2024 election, as Eos reported in October 2024.

“There are a lot of people who believe that science can help us live better lives and that science really does need to be front and center when we’re making public policy,” Jess Phoenix, a volcanologist, science advocate, and former Democratic candidate for the U.S. House of Representatives told Eos at the time.

In March, thousands of people attended Stand Up for Science rallies across the country to protest the misuse of science in federal policy and extensive staffing and funding cuts to scientific agencies. Since President Trump took office in 2025, more than 10,000 PhD-level scientists have left the federal workforce, Science reported in January.

Pew research data shows that public trust in scientists has declined since the COVID-19 pandemic, but it has seen modest improvements since 2023. The latest poll, released in January, found that 77% of adults in the United States have a great deal or a fair amount of confidence in scientists to act in the public’s best interest, compared to 73% in 2023. The percentage is consistently higher among Democrats than Republicans: 90% versus 65%, in 2026. In contrast, only 27% of respondents reported at least a fair amount of confidence in elected officials.

“The last thing I want [is] to become a politician,” wrote one Redditor in response to the Nature story. “But at this rate I may not have a choice if current politicians keep screwing it up.”

—Emily Gardner (@emfurd.bsky.social), Associate Editor

These updates are made possible through information from the scientific community. Do you have a story about how changes in law or policy are affecting scientists or research? Send us a tip at eos@agu.org.

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  • ✇Eos
  • Eddy or Not: Do Eddies Actually Transport That Much Carbon? Nathaniel Scharping
    Source: Global Biogeochemical Cycles The biological carbon pump moves carbon from near the ocean’s surface to deeper regions, maintaining the upper ocean’s ability to absorb carbon from the atmosphere. One component of this system is driven by eddies, or relatively small-scale circular water currents powered by physical instabilities within the ocean. Previous estimates have suggested the eddy subduction pump may play a large role in moving carbon deep into the ocean, but the absence of glob
     

Eddy or Not: Do Eddies Actually Transport That Much Carbon?

17 April 2026 at 12:49
A satellite image of the ocean shows various shades of blue swirls.
Source: Global Biogeochemical Cycles

The biological carbon pump moves carbon from near the ocean’s surface to deeper regions, maintaining the upper ocean’s ability to absorb carbon from the atmosphere. One component of this system is driven by eddies, or relatively small-scale circular water currents powered by physical instabilities within the ocean. Previous estimates have suggested the eddy subduction pump may play a large role in moving carbon deep into the ocean, but the absence of global synthesis leaves the question open.

With data from a worldwide network of remote sensors, Keutgen De Greef et al. captured the eddy subduction pump in action around the globe. Their analysis shows that this pump carries less than 5% of the overall organic carbon transported by the biological carbon pump, meaning it’s of secondary importance to understanding ocean carbon flows.

The authors used data spanning 2010 to 2024 from 941 Argo floats drifting autonomously around the globe. They found 1,333 eddy subduction events below 200 meters. Adding up the contribution of a subset of these they identified as carbon subduction events, they estimated the eddy subduction pump exports 0.05 petagram (~50 million metric tons) of carbon per year from the ocean surface. Carbon subduction hot spots exist at mid- to high latitudes in the Southern Ocean and subpolar North Atlantic, both of which also exhibited a strong seasonal peak in spring. The authors also noted a correlation between eddy kinetic energy and physical subduction events (when surface waters sink below the mixed layer), providing insights into the mechanisms driving the eddy subduction pump

The study comes with some limitations, including the sparsity of data in ocean regions including much of the Pacific, the South Atlantic, and the southern Indian Ocean, which could lead to those regions’ contributions being underestimated. The Argo floats measure particulate carbon levels but are unable to effectively measure dissolved organic carbon, meaning some carbon export is being missed. But given the minimal contribution of the eddy subduction pump, these factors may not significantly change estimates of overall biological carbon subduction, the authors suggest. (Global Biogeochemical Cycles, https://doi.org/10.1029/2025GB008912, 2026)

—Nathaniel Scharping (@nathanielscharp), Science Writer

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Citation: Scharping, N. (2026), Eddy or not: Do eddies actually transport that much carbon?, Eos, 107, https://doi.org/10.1029/2026EO260119. Published on 17 April 2026.
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  • Mediterranean Mussel Farming Could Collapse by 2050 Sarah Stanley
    Source: Earth’s Future Greenhouse gas emissions are heating our atmosphere and oceans, and turning seawater more acidic. One of the myriad expected impacts of these conditions is a reduction in farming yields of shellfish, such as oysters and mussels. Coastal communities worldwide rely on these organisms for their economies and as a major food supply. However, exactly how climate change will affect oyster and mussel farming is not yet clear. Using a novel experimental setup, Pernet et al.
     

Mediterranean Mussel Farming Could Collapse by 2050

17 April 2026 at 12:48
Four small docks overlook a waterfront. In the distance, wooden structures, shellfish farms, are visible in the water. The sky is pale.
Source: Earth’s Future

Greenhouse gas emissions are heating our atmosphere and oceans, and turning seawater more acidic. One of the myriad expected impacts of these conditions is a reduction in farming yields of shellfish, such as oysters and mussels. Coastal communities worldwide rely on these organisms for their economies and as a major food supply. However, exactly how climate change will affect oyster and mussel farming is not yet clear.

Using a novel experimental setup, Pernet et al. report new projected yields of oyster and mussel farming in the Mediterranean Sea for the years 2050, 2075, and 2100. Their results suggest that by 2050, yields of both shellfish will drop dramatically, with mussel production perhaps collapsing altogether.

Most prior studies have assessed shellfish in tank experiments under fairly idealized conditions that do not adequately reflect real-world aquaculture settings. This research team took a different approach. They developed a novel system for exposing oysters and mussels in tanks to realistic conditions using water pumped in from the sea, meaning the animals would experience fluctuations in acidity, temperature, and nutrients similar to those experienced by shellfish on nearby farms.

The researchers set up 12 experimental tanks on the French Mediterranean coast in the Thau lagoon, where shellfish farming is key for the local economy. In three tanks, oysters and mussels were exposed directly to pumped-in seawater under present, ambient conditions. The rest of the tanks received seawater that was first warmed and acidified in accordance with widely accepted climate projections for 2050, 2075, and 2100, with three tanks for each year.

The survival rate of oysters in the tanks with predicted 2100 conditions dropped by 7% compared to present rates, and their growth rate dropped by 40%. These results suggest that yields of farmed oysters in the Mediterranean could drop severely over the next several decades.

The mussels fared even worse. In fact, compared to oysters, mussels have a lower range of water temperatures in which they can survive, and the upper limit is already being exceeded in some summertime Mediterranean waters, leading to mass-mortality events. In the experimental tanks under present conditions, mussel mortality was about 40%, and nearly all mussels died under predicted 2050 conditions.

On the basis of these findings, the researchers call for the urgent development of strategies to protect Mediterranean shellfish farming, such as relocating mussel-farming operations to the cooler waters of open seas or developing cofarming with algae to increase resilience to climate change. (Earth’s Future, https://doi.org/10.1029/2025EF005992, 2025)

—Sarah Stanley, Science Writer

The logo for the United Nations Sustainable Development Goal 14 is at left. To its right is the following text: The research reported here supports Sustainable Development Goal 14. AGU is committed to supporting the United Nations 2030 Agenda for Sustainable Development, which provides a shared blueprint for peace and prosperity for people and the planet, now and into the future.
A photo of a telescope array appears in a circle over a field of blue along with the Eos logo and the following text: Support Eos’s mission to broadly share science news and research. Below the text is a darker blue button that reads “donate today.”
Citation: Stanley, S. (2026), Mediterranean mussel farming could collapse by 2050, Eos, 107, https://doi.org/10.1029/2026EO260121. Published on 17 April 2026.
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