(upbeat music)
- [Narrator] Land west of Phoenix looked like this in 2002.
Now it's covered in buildings.
Phoenix, along with Las Vegas,
is experiencing a stretch of triple digit temperatures
made worse by a heat dome.
- [Reporter] Record level temperatures
shows no signs of letting up.
- [Reporter] Unrelenting grip on the country.
- A lot of our cities have gotten bigger
in the last 20 years, especially in the southwest.
- [Narrator] Here's what happens
when heat domes form above cities
and how urban growth can make that heat even more deadly.
In Phoenix, over 20 days in July
have been at or above 110 degrees.
And space technology company, Maxar
which has been tracking the weather
predicts the city will hit at least 30
by the end of the month.
In Las Vegas, 16 days are predicted to hit that high.
That heat is driven in part by urban development.
- Imagine a city as an island with pavement, roads,
surfaces, glass and steel buildings.
All of these surfaces reflect sunlight
and that heat energy from the sun back into the air around.
- [Narrator] These highly developed areas
can see midday temperatures that are 15 to 20 degrees warmer
than surrounding vegetated areas.
We can see how these heat islands formed
by looking back at Phoenix.
Here it is 23 years ago
but after two decades of urban growth
the city has ballooned.
Back in 2000, Las Vegas looked like this
and now its city limits have expanded.
That expansion paralleled their economic growth
but more infrastructure turned up the heat.
- These are all places where heat gets trapped, right?
So in many of these cities, there's not a lot of breezes.
There's not a lot of shade or trees, and so as a result
heat can build up in these urban corridors.
- It's sometimes hard to grow trees in the west
especially in very arid places
and the native trees that grow there
may not be great at providing shade.
So you have a lot of areas that get a lot of sun.
- The other important thing about plants and trees
and vegetation and even grass
is they cycle moisture from the ground into the air
and help just a little bit, keep things cooler.
- [Narrator] That's driven Thompson, Phoenix
and Las Vegas even higher
and drove the creation of these heat islands.
But that's not the only thing fueling the hot weather.
- When you have a heat dome on top of this
it really intensifies the temperatures
for everyone living in this city.
- [Narrator] These domes are a natural weather phenomenon
and for most of July, one has been covering the southwest.
- A heat dome is a large ridge of high pressure
high in the atmosphere, that basically traps
a lot of hot air underneath it
and it can last for a long time.
Over time, the heat dome is basically reinforcing itself
in the sense that any moisture on the ground or in the soil
that may come up into the atmosphere
that perhaps could cause some
rain or rainstorms in the afternoon
that's going away.
The soils are drying out, the land is drying out
and so this hot air is making things worse and worse.
- [Narrator] The combination of a heat dome
on top of a heat island
means that being outside can be even more dangerous.
Burn centers have reported injuries
to people who touch hot door handles
and walk barefoot on scorched pavement.
- These are hot places, right?
And so there's often this feeling of
well, it's always been hot here
we're used to it, we can deal with it.
But I think that masks some of the really significant risks
that are faced by people experiencing homelessness
by people who are elderly, people who work outside.
Many of these different groups
that are exposed and vulnerable
- [Reporter] In cities already experiencing
triple digit temperatures
The National Oceanic and Atmospheric Administration
is preparing officials for increasing heat events.
- Everybody is very concerned about the future
that with warming and with climate change
we expect more of these events to happen.
And when these events happen, they're more intense.
- [Narrator] And scientists say the heat is here to stay.
- As architects, planners, and engineers look to the future
they have to take into account
the effects of climate change over time
temperatures that are rising
storms and other things that are happening as well.
So they're taking these things into account
with new kinds of technologies,
green roofs that can absorb and cool buildings
and also just in the design and shape of buildings
that can provide more shade and maybe just have
a little bit of resiliency toward a warming climate
that we're all facing in the future.
(upbeat music)