Water moves through plants and back into the atmosphere with unexpected speed

A study from Chapman University provides the first comprehensive global estimates of water storage in Earth’s vegetation and the time it takes for that water to flow through plants. The research fills a critical gap in our understanding of the global water cycle and its sensitivity to climate and land-use changes.

Published in the journal Nature Water, the study reveals that Earth’s vegetation holds about 786 km³ of water, a mere 0.002% of Earth’s total freshwater.

However, the significance lies in the rapid movement of water through plants. This transit time, from absorption to release into the atmosphere, is among the fastest in the water cycle – ranging from five days in croplands to 18 days in evergreen needleleaf forests.

For perspective, water in lakes takes around 17 years to cycle, and in glaciers, the process spans 1,600 years.

Continuous loop of Earth’s water cycle

Earth’s water cycle, or hydrological cycle, is the continuous movement of water through the environment. It begins with evaporation, where the sun heats water from oceans, lakes, and rivers, turning it into vapor.

This vapor rises into the atmosphere and cools, leading to condensation, which forms clouds. When the clouds become heavy, water returns to Earth as precipitation in the form of rain, snow, or hail.

Once on the ground, water either flows over the surface into rivers and lakes (runoff) or seeps into the soil (infiltration).

Plants also play a role by releasing water vapor into the air through transpiration. Together, these processes recycle water, connecting oceans, land, and the atmosphere in a continuous loop.

A forgotten element of the water cycle

“Plants are the forgotten part of the global water cycle,” noted Dr. Andrew Felton, lead author and professor at Montana State University. Despite their critical role in returning water from the ground to the atmosphere, plants are often excluded from water cycle diagrams.

“Our results show that the transit of water through plants occurs on the order of days, rather than months, years, or centuries, as it does in other parts of the water cycle,” said Dr. Felton.

By combining plant water transit estimates with those for the atmosphere (8–10 days) and soil (60–90 days), researchers can now approximate the total time a drop of water spends in the terrestrial cycle.

Intensification of the water cycle

One striking finding is the rapid transit of water through croplands. During peak growing seasons, water cycles through crops in less than a day. This speed, consistent across global croplands, hints at a broader environmental implication.

“Land use change may be homogenizing the global water cycle and contributing to its intensification by more rapidly recycling water back to the atmosphere where it can turn into heavy rain events,” explained Dr. Gregory Goldsmith, senior author and associate professor at Chapman University.

Water dynamics in Earth’s vegetation

The research team utilized data from NASA’s Soil Moisture Active Passive Mission (SMAP), a satellite program designed to measure soil moisture across Earth’s surface.

SMAP data accounted for vegetation interference, which the satellite originally treated as noise to correct soil moisture readings. However, the researchers discovered that these corrections held important information about the amount of water stored in plants.

By analyzing this overlooked data and combining it with advanced measurements of how quickly water exits plants, the team developed detailed estimates.

These included five years of monthly data on plant water storage and the time water takes to move through vegetation, calculated with a spatial resolution of 9 square kilometers (approximately 3.5 square miles).

This high-resolution analysis provided a remarkable understanding of water dynamics within Earth’s vegetation.

Implications for a changing planet

The study highlights the sensitivity of plant water transit times to environmental events like deforestation, drought, and wildfires.

“The results suggest that the transit time of water through plants is likely to be very sensitive to events such as deforestation, drought and wildfire, which will fundamentally change the time it takes for water to flow through the water cycle,” said Felton.

By shedding light on the dynamic role of vegetation, this research highlights the interconnectedness of ecosystems and the urgent need to understand how land-use changes influence the global water cycle.

As the planet faces intensifying climate challenges, studies like this pave the way for more informed strategies to manage water resources and predict environmental shifts.

The study is published in the journal Nature Water.

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