Where Does Water from Snow and Rainfall Actually Go?

Here’s a question that matches the old “If a tree falls in a forest and no one hears it, does it make a sound?” question. But this one is less abstract. If rain or snow falls on land, where does it eventually go?

If your answer is that it turns into runoff that ends up in waterways and eventually flows into the oceans, you’re only partially right. Only about a quarter of the precipitation over land does that. So what happens to the rest?

University of Utah researchers have the answer, and even some precise numbers.

In an article in the journal Science, they report that of the remaining water, most of it — 64 percent — is exhaled back into the atmosphere by plants, in a process called transpiration. Based upon previous studies, another 27 percent lands on leaves and evaporates, and the rest evaporates from soil (6 percent) or from lakes, rivers and streams (3 percent).

The findings actually were a bit of a surprise, because previous research suggested that even more of the water — as much as 80 percent — was accounted for by plant transpiration.

The researchers used hydrogen isotope ratios of water in rain, rivers and the atmosphere from samples and satellite measurements to come up with their numbers.

“It’s important to understand the amount of water that goes through each of these pathways,” one of the study’s authors, University of Utah hydrologist Stephen Good, explained in a press release. “The most important pathway is the water that passes through plants because it is directly related to the productivity of natural and agricultural plants.”

The researchers also found that of the precipitation that seeps down into the Earth’s groundwater, most moves through the soil so quickly that it isn’t available for plants to use. Only 38 percent of the water ends up being involved in moving nutrients, fertilizers or contaminants, or in affecting biological processes.

From Discovery News