Why is Austin like that?

The Gulf of Mexico is a big, warm body of salt water south and east of Austin. The sun heats it, and lots of water turns into water vapor (water so spread out that it floats in the air like an invisible gas). In summer, the wind in Central Texas often blows from the south and southeast. That wind is like a conveyor belt. It carries the wet Gulf air all the way to your street.

Air full of water vapor is called humid. Humid air feels sticky because the sweat on your skin dries slowly. Drying sweat is how your body cools off, so humid days feel hotter than the number on the thermometer.

• High sun. Austin is far south in the United States. In summer the sun climbs high and shines down almost straight. Straight-down sunlight heats the ground more than slanted sunlight.
• Warm nights. Dry air lets the day’s heat escape into space at night. Humid air works more like a blanket. It holds heat in, so Austin nights stay warm.
• Heat-soaking stuff. Roads, roofs, parking lots and walls soak up heat all day and let it out slowly at night. That is why a city can stay warmer than the countryside after dark.
• Heat domes. Sometimes a big area of high pressure sits over Texas for days. The air under it sinks and warms, and it blocks clouds and rain. Sunny day follows sunny day.

Cicadas are big bugs with clear wings. On each side of a male cicada’s body is a stiff, ridged patch called a tymbal (say it “TIM-bull”). A muscle pulls the tymbal in, and it pops. When the muscle lets go, it pops back. This happens hundreds of times a second, so the clicks blur into one long buzz.

A male’s body is mostly hollow inside, like a drum. The hollow space makes the sound louder. Some cicadas are among the loudest bugs on Earth. They sing most on the hottest days, which is why their buzz sounds like summer in Austin.

Young cicadas, called nymphs (say it “nimfs”), live underground for years, sipping juice from tree roots. Then they crawl out, climb a tree, and split out of their old skin. You might find the empty shells stuck to tree bark.

The bats are Mexican free-tailed bats. In the early 1980s, after the bridge was fixed up, its underside had lots of narrow gaps. Those gaps are dark and snug, a bit like a cave. Bats moved in, and more and more came.

Today it is called the largest city bat colony in the world. Scientists estimate up to about one and a half million bats live there in summer. Most of them are mother bats raising their babies, called pups.

At dusk, the bats pour out in long, twisting ribbons and fly off to hunt flying insects through the night. When the weather turns cold in fall, most of them fly south toward Mexico. They come back in spring.

A very long time ago, long before people, warm shallow seas covered much of Texas. Tiny sea creatures and shellfish lived and died there. Their shells, made of the same stuff as chalk, piled up on the sea floor. Over a very long time, the layers pressed together and turned into rock called limestone.

That is why people around Austin sometimes find fossil shells in rocks. West of town, the land rises into the Hill Country, where this limestone pokes out everywhere.

Limestone has cracks and holes, and rainwater can slowly dissolve it to make bigger tunnels. When rain falls in the hills, some of it sinks into the cracks and flows underground. This giant underground water-holding rock is called an aquifer (say it “AK-wih-fur”). Austin’s is part of the Edwards Aquifer.

Underground, the water is far from the summer sun and the winter wind. So it stays about the same temperature all year, around 68 to 70 degrees. When it bubbles up at Barton Springs, it feels cold on a hot day and almost warm on a cold one.

A tiny creature called the Barton Springs salamander lives in and around these springs and nowhere else in the world.

The trees Austin people call “cedar” are really a kind of juniper, called Ashe juniper. In winter, many of them grow thousands of tiny cones at the tips of their branches. Those cones turn the trees orange-brown. When a cold front blows in, the wind shakes the cones, and pollen puffs out in little clouds that can look like smoke.

Pollen is a fine powder that plants use to make seeds. Juniper pollen is so light the wind can carry it a long way.

The middle of North America is wide and fairly flat, with no tall mountain wall running east to west. So cold air from Canada can slide all the way south to Texas. When it pushes into our warm, wet air, the temperature can drop fast. Texans call a strong one a blue norther.