Spring is the season of water. The world starts to wake up as the sun beats down stronger, but the buds and the leaves wait for rain. We finally had a good soaking storm announce the arrival of the season with thunder interrupted sleep just the other night. Saint Paul is waking up to the water. But how that storm gets here is a story in itself, the story of planet that defines itself by life and the movement of water from one Spring to another.
Water is a strange molecule. A chemist will write it as H₂O, an oxygen atom connected to two hydrogens. An arrangement like this has a “molecular weight” of only 18 based on its composition, and by all rights it should be much lighter than the major components of our atmosphere Nitrogen (N₂, weight 28) or Oxygen (O₂, weight 32). The water should want to fly away to the upper reaches like Helium does.
The reason that water pools on the ground is the tension between the simple atoms that make it up. The bonds that tie the hydrogen to oxygen are made of electrons, and an odd quirk of statistics makes them want to stay closer to the oxygen. The result is that water, unlike other simple molecules, has a kind of electrical charge. The hydrogens are positive, electron lacking, and the oxygen is negative, electron rich. That causes the molecules to stick together and prefer to stay as a liquid where they slide past each other rather than bounce aimlessly, as a gas would.
That simple tension and the resulting charge makes life on the land of this planet possible.
We have a lot of water on Earth, so the atmosphere usually carries about as much as it can. While water prefers to settle in as a liquid, there is delicate balance between gas and liquid at any given set of conditions. The difference between the two is nothing more than heat from the sun. A relatively shallow body of water like the Gulf of Mexico becomes a bit hotter when it turns toward the sun, so the water heats up and moves into the air. Think of it as a very slow boil, a simmer you can barely see multiplied by the sheer size of the Gulf.
When water reaches the air, it behaves more or less as you would expect a gas of its kind to do – it rises above the rest of the heavier atmosphere. It eventually hits a place where there is much less of the other air around it and the pressure is low. At that point, it can shed the heat that was absorbed at the surface of the planet and start puddling back into a liquid. It starts as a mist that is still too light to fall, but with enough water the high mist thickens and becomes a cloud. It can travel long distances on the winds of the upper atmosphere driven by Earth’s rotation before this happen and may encounter colder air further north that speeds the process along. The water then falls as rain.
Here in Saint Paul, the vast majority of the rain that we see came up from the Gulf of Mexico. The Mississippi, Missouri, and Ohio watersheds are over 95% closed systems, made up of water that does nothing more than wash down the rivers to the Gulf of Mexico, waiting for the sun to pick it back up and start the journey over. Very little water can rise high enough to clear the Rocky Mountains to our west, and the winds do not bring much in from the Atlantic to the east. The reach of this cycle of rain defines the wet “land of lakes”, what Minnesota means in the Dakota language, and where it dos not go defines the dry high plains to our west.
All of this happens because of how the electrons are distributed in a simple molecule that happens to be very plentiful on this planet. All of this happens on a scale that is both too large and too small for us to much more than observe and wonder.
Modern science has explained this behavior and why the rain falls as it does very well over the last century or so. Before that time, it all seemed a bit mysterious. Humans used to rely on a deep intuition that somehow we were caught in the middle of a cycling balance of forces and prayed to God or Gods to push them one way or the other.
As much as science has been able to explain just what makes water so very special and what brings it to us, we can still use those instincts to relate to the arrival of liquid water every Spring. We are in the middle of a strange balance and a simple tension between forces that are not immediately obvious because we are both too big and too small to see them. As Saint Paul becomes green with the perfume of Spring, it’s worth spending a few moments getting to understand the intuition that taught us the lesson long before we could prove it was true.