Landsat at 50: How satellites revolutionized the way we see – and protect – the natural world

The Belo Monte Dam’s construction, shown here in 2012, flooded land and changed the river. Mario Tama/Getty Images^[6]

When work began on the Belo Monte Dam project in the Brazilian Amazon in 2015, Indigenous tribes living along the Big Bend of the Xingu River started noticing changes in the river’s flow. The water they relied on for food and transportation was disappearing.

Upstream, a new channel would eventually divert as much as 80% of the water to the hydroelectric dam, bypassing the bend.

The consortium that runs the dam argued that there was no scientific proof that the change in water flow harmed fish.

But there is clear proof of the Belo Monte Dam project’s impact – from above, write Pritam Das^[7], Faisal Hossain^[8], Hörður Helgason^[9] and Shahzaib Khan^[10] at the University of Washington. Using satellite data from the Landsat program, the team showed how the dam dramatically altered^[11] the hydrology of the river.

The front satellite image shows the Big Bend of the Xingu River on May 26, 2000, before the Belo Monte Dam project began. Move the slider to the left to see the same region on July 20, 2017.

“As scientists who work with remote sensing, we believe satellite observations can empower populations around the world who face threats to their resources,” Das and his colleagues write.

Read more: Satellites over the Amazon capture the choking of the ‘house of God’ by the Belo Monte Dam – they can help find solutions, too^[12]

It’s hot in the city – and even hotter in some neighborhoods

A street fan provides relief on a hot summer day in New York City. Stephen Chernin/Getty Images^[13]

Landsat’s instruments can also measure surface temperatures, allowing scientists to map heat risk street by street within cities as global temperatures rise.

“Cities are generally hotter than surrounding rural areas, but even within cities, some residential neighborhoods get dangerously warmer than others just a few miles away,” writes Daniel P. Johnson^[14], who uses satellites to study the urban heat island effect at Indiana University.

Neighborhoods with more pavement and buildings and fewer trees can be 10 degrees Fahrenheit (5.5 C) or more warmer than leafier neighborhoods, Johnson writes. He found that the hottest neighborhoods tend to be low-income, have majority Black or Hispanic residents and had been subjected to redlining, the discriminatory practice once used to deny loans in racial and ethnic minority communities.

Comparing maps of New York City’s vegetation and temperature shows the cooling effect of parks and neighborhoods with more trees. NASA/USGS Landsat^[15]

“Within these ‘micro-urban heat islands,’ communities can experience heat wave conditions well before officials declare a heat emergency,” Johnson writes.

Knowing which neighborhoods face the highest risks^[16] allows cities to organize cooling centers and other programs to help residents manage the heat.

Read more: Landsat zooms in on cities' hottest neighborhoods to help combat the urban heat island effect^[17]

The making of ghost forests

The white trunks of a ghost forest mark a coastal North Carolina landscape. Emily Ury, CC BY-ND^[18]

Satellites that scan the same areas year after year can be crucial for spotting changes in hard-to-reach regions. They can monitor snow and ice cover, and, along U.S. Atlantic coast, dying wetland forests.

These eerie landscapes of dead, often bleached-white tree trunks have earned the nickname “ghost forests.”

Emily Ury^[19], an ecologist now at the University of Waterloo in Ontario, used Landsat data to spot wetland changes. She then zoomed in with high-resolution images from Google Earth – which includes Landsat images – to confirm that they were ghost forests.

“The results were shocking. We found that more than 10% of forested wetland^[20] within the Alligator River National Wildlife Refuge [in North Carolina] was lost over the past 35 years. This is federally protected land, with no other human activity that could be killing off the forest,” Ury writes.

Landsat’s view of the Alligator River and refuge shows signs of ghost forests on the east side of the river. NASA Earth Observatory^[21]

As the planet warms and sea levels rise, more salt water is reaching these areas, increasing the amount of salt in the soil of coastal woodlands from Maine to Florida. “Rapid sea level rise seems to be outpacing the ability of these forests to adapt to wetter, saltier conditions,” Ury writes.

Many more stories can be found in Landsat’s images, such as an overview of the war’s effects^[22] on Ukraine’s wheat crop, and how algae blooms have spread in Florida’s Lake Okeechobee^[23]. Countless projects are using Landsat data to track global change and possibly find solutions to problems, from deforestation in the Amazon^[24] to the fires that have put Alaska on pace for another historic fire season^[25].

An artist’s rendering of Landsat 8. NASA/Goddard Space Flight Center Conceptual Image Lab^[26]

Read more: Sea level rise is killing trees along the Atlantic coast, creating 'ghost forests' that are visible from space^[27]

Authors: Stacy Morford, Environment + Climate Editor

Read more https://theconversation.com/landsat-at-50-how-satellites-revolutionized-the-way-we-see-and-protect-the-natural-world-186986

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