I’ve grown very fond of my rain jacket during the past few weeks. It’s a typical yellow slicker, slightly too long in the arms, and when I wear it, as I have nearly every day, I become a well-protected turtle. The real turtles are having a great time with all this precipitation, along with the newts and salamanders that come to life during the season of vernal pools.

Where does all this rain come from? I won’t go into the intricate machinations of the weather, the stationary lows and intermittent highs that TV weather broadcasters point to on brightly colored maps. Today I’m interested in what makes rain occur and what happens to it when it hits the earth.

We live in a windy world. The differences in pressure between cold and hot air generate wind. Wind has energy. It picks up microscopic dust particles from the Sahara Desert in Africa or the great deserts of China and whirls them upward into the atmosphere.

The atmosphere also contains water vapor. One of the more significant greenhouse gases in the atmosphere, in fact, is H2O, which retains heat so well. When water vapor hits a very small particle of dust it condenses around it. That tiny blob of water then bumps into another blob, and another, and so forth. When they reach a certain size, approximately 1 millimeter in diameter, water droplets fall from the sky.

Seems simple, but scientists, like small children, always want to know more — how does this actually work? 

The inside of a cloud is a rough place, full of strong air currents and turbulence. The turbulence creates many small swirls of air. Due to centrifugal force, these little whirlpools spin tiny water droplets out to their edges, where they bang together in clusters. The clusters of water eventually become about a millimeter in size, which is the size at which raindrops begin to fall. 



Of course, falling from a great height is no easy journey for the raindrop. It starts out as a nice round sphere, held together by the weak hydrogen bonds between the H2O molecules. Then gravity takes over. On its way to the ground the raindrop hits other raindrops and grows a bit larger. That may be good for a bank but in the world of raindrops, none are “too big to fail.” Once the raindrop reaches approximately 4 millimeters in diameter, the hydrogen bonds can’t keep all the molecules together. The raindrop breaks apart into multiple smaller-sized droplets. 

Individually, raindrops are an efficient way to move moisture from the atmosphere to the ground. When they hit the ground, however, problems can occur. I’m not talking about floods, houses toppling into rivers or cars crumpling like tissue paper. The problem that I worry about is nearly invisible. It happens at this time of year when the spring rains fall and people begin to apply all sorts of noxious chemicals to their lawns in a pursuit of the perfect green patch. 

Ortho Bug B Gon, Triazicide Insect Killer for Lawns, Weed and Feed — these easily acquired chemicals and pesticides kill insects and certain weeds in our lawns. Improperly applied, such as right before a rainstorm, or applied in excess, they don’t stay on a lawn. They will move with the water that falls from the sky.

An inch of rain falling over an acre of land equals 27,154 gallons of water. Some of that water is absorbed by the soil and sinks deep into the water table. But some of it also escapes the land, moving to the nearest stream or lake. And it carries with it what we deliberately place on our gardens and lawns, whether that is RoundUp or compost. The atmosphere has brought us a lot of raindrops in recent weeks. Let’s try to keep those drops as clean as when they first fell.