This story was originally published by
Wired.
A river is a mercurial thing, running deep and fast in the rainy
season, and low and slow when the rains fade. It can dry up
completely one year, then turn into a raging flood the next.
Every so often, a river disappears entirely, bringing down the
communities it once nourished.
You hear a lot about how climate change is fueling the rise of
our seas, but not so much about how it will transform our
rivers, the flooding of which currently affects almost 60
million people a year. An ambitious new study in Nature Climate
Change, though, takes on the task of modeling rivers’ reactions
to a warming world. With their projections of flooding severity,
the researchers were able to quantify possible losses of both
property and human life. As with any climate model, the
researchers are making assumptions to present just one possible
future scenario—but even in the best case, things don’t look
pretty.
Seemingly against reason, climate models have projected that on
a warmer planet, storms will dump more water. Why? “The warmer
the air, the more moisture it can hold,” says climate scientist
Judah Cohen, who wasn’t involved in the research. “It’s just
like you build a bigger pool—it can hold more water.”
In general, when that water dumps, it dumps hard, swelling
rivers and causing flooding. “It then gets much more
complicated,” Cohen says. “Warming could maybe change the
dynamics of the atmosphere, so that you’re getting fewer and
fewer storms.” In Southern California, for instance, climate
models predict that storms will be more intense, but also less
frequent.
For this new model, the researchers looked at worldwide impacts
of fiercer storms by marrying climate models and models of river
flows. “The output of the climate model may be rainfall, for
example, and that’s the input for the river flow models,” says
climate scientist Richard Betts, of the University of Exeter,
coauthor on the new paper. “That then calculates the water flow
down river channels in all the major basins around the world.”
The researchers further modified those outcomes based on
different global temperature projections: a 1.5 degree C
increase (the idealistic goal of the Paris Climate Agreement), 2
degrees, and 3 degrees.
“What we did is take those outcomes and then look at what the
maximum river flows meant in terms of flooding impacts,” says
Betts. By looking at population and development data, they could
project that forward to predict how many people and how much
property would be at risk as climate change periodically swells
the rivers of Earth.
The projections are not encouraging. If humanity can hold global
temperature rise to 1.5 degrees C—and many climate scientists
think it may already be too late for that—loss of life from
river flooding could go up as much as 83 percent from the
current yearly average of 5,700. For 2 degrees, that jumps to as
much as 134 percent; 3 degrees, 265 percent.
As for damages, the global average from river flooding is
currently about $110 billion a year. With a 1.5 degree rise, the
models predict that could jump 240 percent; for 2 degrees it’s
520 percent, and for 3 degrees it’s a stunning 1,000 percent
increase, or a new total of $1.25 trillion a year. Under a
slightly more optimistic scenario, which projects slower
economic growth, those figures would be lower by about a third.
Still, not a good outlook.
This does not mean, though, that every region will fare equally.
The developing world, where infrastructure isn’t as strong, is
more at risk. Population growth is also a factor, as crowding
exposes more people to flooding. That’s more intense in South
Asia than North America, for example. On the other hand, the
models show that a region like Eastern Europe may see a decrease
in maximum river water flow.
“In other places, Brazil for example,” says Betts, “parts of the
country are projected to see an increase in flooding risk. But
Brazil is a huge country, and they tend not to be the places
where there’s so many people.” The models also assume certain
population and development projections will hold.
They also assume that humans won’t take steps to mitigate the
risks of flooding. “There’s an important point here, that you’re
assuming that these things don’t change in the future, which in
reality they probably would as part of adaptation,” says Betts.
Maybe river populations will build out better infrastructure and
warning systems to protect themselves. But that introduces a
whole new set of uncertainties—financial and political ones.
“Anything about the future is uncertain, but I think with this
kind of river flooding, there’s even more challenges to it,”
says Cohen. “They’re taking both the meteorological aspect of
it, which I think has a lot of uncertainty, and then multiplying
that by the economic uncertainty.”
Scientists scrutinize the past and present and extrapolate that
forward as best they can. And from the looks of this new study,
humanity would do well to prepare itself both for higher seas
and angrier rivers. In these times of uncertainty, it certainly
wouldn’t hurt. |
