How global greening could drain Earth’s water supply

From space, Earth looks lusher than it did a generation ago. Satellite records show that leaf area has expanded across most of the planet since the early 1980s – a phenomenon popularly called “global greening.”

It sounds like unambiguously good news: more foliage to soak up carbon, more habitat, more shade. But a new analysis throws a bucket of cold water on such an optimistic view.

In many places, greener landscapes have gone hand in hand with drier soils, especially where water is already scarce. The paradox is simple: plants that flourish also tend to drink more.

Four decades of data

The research team stitched together four decades of evidence – multiple satellite records of vegetation, modern climate datasets, and simulations from a dozen Earth system models.

They used these to tease out cause and effect between plant growth and soil moisture.

Looking from 1982 through the end of this century, they asked a straightforward question with big consequences: what usually happens to the water held in the ground when vegetation ramps up?

Greener landscapes, more water

Their answer is sobering. About two-thirds of the world’s vegetated land has greened since the early 1980s, but nearly half of those greener areas have also dried out below the surface.

That “greening–drying” pattern shows up most clearly in Central Africa, Central Asia, eastern Australia, and swaths of mid- to high-latitude Europe – places where rainfall is fickle and heatwaves are becoming more punishing.

There are brighter spots. Parts of North America, the Indian Peninsula, and the southern Sahel buck the trend, showing “greening–wetting,” where extra leaves coexist with moister soils. But the overarching story is that more vegetation often means a thirstier landscape.

Lush growth dries the land

Why would that be? Plants are living pumps. To photosynthesize, they open microscopic pores on their leaves to draw in carbon dioxide.

Water escapes through those same pores, a process called transpiration. Add more leaves or extend the growing season and you boost the total draw on the local water budget.

In wet climates with regular recharge, the added demand can be balanced by rainfall and snowmelt. In drylands, or in places where warm-season rains have weakened, the balance tips the other way. Soil moisture is the first line of credit, and it gets depleted.

Rising CO2, land management, and warming have boosted global leaf area, lengthening growing seasons and adding vegetation worldwide. Trees can shade and save soil moisture, but in water-limited regions, added transpiration often outweighs those benefits.

The atmosphere’s rising “thirst” under warming – meteorologists call it higher vapor pressure deficit – adds yet another straw to the same glass. When the air can hold more moisture, it pulls harder on leaves and soils alike.

Losing Earth’s natural water buffer

The consequences ripple well beyond a wilting lawn. Soil moisture is the quiet buffer that keeps crops from failing between rains, feeds streams weeks after a storm, and tamps down wildfire risk.

As that buffer shrinks, irrigation demand rises, late-season flows dwindle, and heat extremes become more dangerous because dry soils can no longer shed heat through evaporation.

Ecologically, greener-but-drier can rearrange communities. Woody encroachment in savannas may squeeze out grasses that grazers need. In northern forests, faster spring growth may be offset by late-summer stress that leaves trees susceptible to pests and fire.

A climate fix with tradeoffs

It’s tempting to read greening as a climate solution in its own right. And in many contexts – protecting existing forests, restoring wetlands, planting the right trees in the right places – nature is absolutely part of the answer.

What this study adds is nuance: greening is not automatically good for water. In cities, for example, more urban canopy cools streets and cleans the air, but it also increases transpiration. If the species mix is ill-suited to local rainfall, or irrigation relies on potable water, the fix can create its own strain.

On farms, hedgerows and windbreaks can improve microclimates and reduce evaporation from bare soil. Yet high-water-use species planted at large scale in arid basins may cut into already stretched rivers.

Future feedbacks between plants and water

The authors didn’t stop at the past. Using the same blend of observations and models, they projected how vegetation–water feedbacks may evolve through 2100.

In many regions, especially under hotter scenarios, soils become more sensitive to changes in plant activity: a given boost in leafiness more readily drains the root zone.

Where precipitation is expected to increase substantially, that added income can balance the books. Where it isn’t, the greening–drying paradox tightens its grip.

Smarter restoration strategies

None of this argues against restoration or tree planting. It argues for smarter versions of both. A watershed that mixes deep-rooted native species, patches of shade, and open ground can deliver carbon storage, flood mitigation, and cooling without overtaxing local supplies.

Riparian buffers that slow runoff and recharge aquifers do double duty for water and biodiversity. In drylands, species choice matters. Drought-tolerant shrubs and trees with efficient water use can stabilize soils and provide habitat without guzzling what little is available.

Even in humid regions, paying attention to late-summer soil moisture – not just annual rainfall – helps avoid surprises.

Global greening and water security

There’s also a policy undercurrent here. Nature-based solutions are rightly gaining traction in climate plans, but their success will be measured on the ground, not from orbit.

Accounting for water alongside carbon – evaluating how projects alter soil moisture, streamflow, and downwind climate – should be standard practice.

That means monitoring, course-correcting when plantings are too dense or too thirsty, and designing projects at the scale where water actually moves: the watershed.

The picture from space remains compelling: a greener Earth than our parents knew. The view from the ground is more complicated. Leaves are only half the story. Water is the other half, and in a warming world it’s the half we can least afford to ignore.

The study is published in the journal Communications Earth & Environment.

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