Where Does Rain Go After It Falls?

We tend to think of rain as something that simply falls from the sky, soaks the ground and disappears. But once a raindrop reaches the surface, its journey is really just beginning.

Some rain sinks into the soil. Some is absorbed by plants. Some travels deep underground, while some runs across the surface into streams and rivers. Eventually, much of that water returns to the atmosphere or makes its way to lakes and oceans.

Where an individual raindrop goes depends on where it lands, how hard it is raining, what the soil is like and even what happened during the days before the storm.

First Stop: The Soil

When rain lands on bare ground, a lawn, garden or forest floor, some of it begins moving into the soil. This process is called infiltration.

How quickly that happens varies enormously.

Loose, healthy soil with plenty of organic matter generally allows water to soak in more easily. Compacted soil, heavy clay and paved surfaces allow much less water to penetrate. Soil structure and health play an important role in how rain moves through a garden. If the ground is already saturated from previous rain, there may simply be nowhere for additional water to go.

Very dry soil doesn't always absorb water easily either. In some cases, hydrophobic soil can actually repel water, causing it to bead up or run across the surface instead of soaking in.

The intensity of the rain matters too. A gentle rain may soak into the ground almost as quickly as it falls. During a heavy downpour, rain can arrive faster than the soil can absorb it, causing water to collect or begin flowing across the surface. That's why rainfall intensity can matter just as much as the total amount of rain.

Plants Get Some of It

Plants intercept rainfall before it even reaches the ground. Water collects on leaves, branches and stems, and some of that water evaporates directly back into the atmosphere.

Rain that reaches the soil can be absorbed by plant roots. The plant uses some of this water for its biological processes, but a surprisingly large amount eventually returns to the atmosphere through transpiration.

During transpiration, water moves from the roots through the plant and is released as water vapor through tiny openings in its leaves called stomata.

Evaporation from soil and water surfaces combined with transpiration from plants is known as evapotranspiration. It's one of the major ways water returns from land to the atmosphere.

Trees and buildings can also affect how much rain reaches a particular patch of ground in the first place. These localized rain-shadow effects can make rainfall around a yard surprisingly uneven.

Some Rain Keeps Traveling Down

Water that isn't taken up by plants may continue moving deeper into the soil. Eventually, some of it reaches layers of earth and rock that are saturated with water. This underground water is called groundwater.

Groundwater isn't necessarily a giant underground lake. In many places, it occupies tiny spaces and cracks within soil, sand, gravel and rock. The upper boundary of this saturated area is what we call the water table.

Groundwater can remain underground for very different lengths of time. Some moves relatively quickly and eventually emerges through springs or seeps. Other groundwater may remain below the surface for decades, centuries or even longer.

In fact, some groundwater can remain underground for thousands or even millions of years. Here's a closer look at how rain becomes groundwater and how long it can stay there.

It can also supply wells, making rainfall an important source of drinking water in many communities.

When the Ground Can't Take Any More

Not every raindrop soaks into the ground. If rain falls faster than the soil can absorb it—or if the soil is already saturated—the excess begins moving across the surface as runoff.

Runoff follows gravity downhill. Small flows join other small flows, eventually reaching drainage ditches, creeks and streams. Streams feed larger rivers, and rivers may empty into lakes, reservoirs, wetlands or the ocean.

This is why a heavy storm miles upstream can cause a river to rise even if little or no rain fell where you're standing.

Cities can produce especially large amounts of runoff because roofs, roads, sidewalks and parking lots don't absorb water the way soil does. Instead, rainfall is quickly directed into gutters, storm drains and waterways.

What Happens in a Forest?

A forest gives rainfall a particularly complicated route to the ground.

Some rain is caught by leaves and branches. Some evaporates without ever reaching the soil. Water that does make it through the canopy may drip from leaves, run down tree trunks or land on a layer of leaves and organic material covering the forest floor. That layer slows the water down and gives it more time to infiltrate the soil.

Roots, burrowing animals, decaying plant material and microorganisms also help create spaces through which water can move. This is one reason healthy, undisturbed soils can play an important role in slowing runoff and storing rainfall.

Eventually, Much of It Reaches a Larger Body of Water

Follow surface water long enough and much of it eventually reaches a lake or the ocean. But the route may be anything but direct.

A raindrop falling on a hillside might soak into the soil, become groundwater, emerge months later in a spring, enter a creek, flow into a river and eventually reach the ocean. Another drop from the same storm might land on a driveway, enter a storm drain and reach that same river within hours.

Two raindrops landing only a few feet apart can therefore take very different journeys. And even before they hit the ground, individual raindrops can have surprisingly eventful trips through the atmosphere. Here's how far a raindrop can fall and what happens to it on the way down.

Then the Sun Takes Over

Water doesn't stay put forever. Energy from the sun causes water from oceans, lakes, rivers, puddles and damp soil to evaporate, changing from liquid water into water vapor. Plants add still more water vapor through transpiration.

That water vapor rises into the atmosphere. Under the right conditions, it cools and condenses into tiny droplets or ice crystals, forming clouds. Eventually, some of that water may become precipitation again.

The water falling in your yard today could once have been groundwater, river water, lake water or ocean water. It may have passed through soil and plants many times before returning to the atmosphere.

A Raindrop Doesn't Really Have an Ending

The familiar diagram of the water cycle—evaporation, clouds, rain and back to the ocean—makes the process look almost like a neat circle. In reality, water follows countless overlapping routes and travels at very different speeds.

Some rain may be back in the atmosphere within hours. Some may spend a growing season inside soil and plants. Some may enter a river and reach the ocean, while some may seep deep underground and remain there for generations.

And the amount of water beginning that journey can vary even within the same community. Rainfall can differ substantially over surprisingly short distances, particularly during localized showers and thunderstorms.

Rain doesn't simply disappear after a storm. It changes location, changes form and keeps moving through the landscape, living things and atmosphere—eventually becoming part of another cloud and, perhaps, another rainy day.