Water Scarcity - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 108

change is a change in weather patterns over time, from decades to millennia; the change
can be in the average weather for a region, or in the distribution of extreme weather
events.
“Some places used to getting [water] won't, and others that don't, will get more,” said
Dan Nees , a water-trading analyst with the World Resources Institute. “Water scarcity
may be one of the most underappreciated global political and environmental challenges
of our time.”
As temperatures rise, experts say, the demand for water will increase, storms will be-
come more intense, and droughts and floods will occur with greater frequency. Many
hydrologists believe evidence suggests that global warming is speeding up the hydro-
logic cycle—the rate at which water evaporates into the air and falls to the ground as
rain or snow. The implications of this are enormous: as the climate warms, there will be
more rain and less snow; diminished snowpack will lead to changes in runoff patterns
and water supplies; increased evaporation will lead to less soil moisture, which causes
greater erosion, an influx of invasive species, and the spread of pathogens.
Climate change will also change the life cycle of plants, particularly trees. With plen-
tiful rain, plants undergo a growth spurt; in dry periods, they wilt. The extra biomass
that results from a growth period creates dry tinder, which can lead to highly destruct-
ive forest fires. And it entices insects that attack large swaths of woods, such as the bark
beetles that have notoriously decimated 3.5 million acres of pine forests in northwest-
ern Colorado.
USGS scientists who conducted a ity-year survey of forests in the western United
States and Canada found that average temperatures in the West rose by more than one
degree over the last few decades, and that trees were dying twice as quickly in 2008 as
they did in the 1970s. The die-off in old-growth forests had eclipsed the growth of new
trees. Because forests act as “carbon sinks,” this has a double impact: plants take in car-
bon dioxide and release oxygen as they grow, which removes carbon from the atmo-
sphere, but when a tree dies or burns, the carbon it has stored is released back into the
air, which helps to warm the planet.
Though most experts tend to focus on how climate change will affect water quantity,
hydrologists such as USGS's Bob Hirsch point out that it also profoundly affects water
quality. Higher water temperatures, more frequent storms, and shifts in flows affect
aquatic life, pollution levels, oxygen content, and turbidity, among other things. While
Hirsch agrees the planet is warming, he says, “Scientific evidence about the specific
ways it is changing our water resources is still very unclear.”
The 2008 IPCC report highlighted concerns about equatorial regions, particularly in
sub-Saharan Africa, where climate change is adding to desertification. The UN has