Climate Paradox: The drier the land, the faster the seas rise

A new study finds that widespread drying, including freshwater runoff from land into the sea, is the main driver of sea level rise, outpacing the melting of large ice sheets.

Drought and rising sea levels, two seemingly opposite phenomena, but have a complex relationship - Photo: AI

Over-draining of groundwater, prolonged droughts and faster evaporation due to rising temperatures are severely depleting the Earth’s freshwater reserves. A new study finds that “drying up of continents” is contributing to sea level rise faster than melting ice at the poles.

The more severe the drought, the higher the sea level

According to a study published in the journal Science Advances , over the past two decades, surface freshwater resources such as lakes, aquifers and soil moisture have been severely depleted. The main causes are climate change, rising temperatures causing faster evaporation, prolonged droughts and over-extraction of groundwater.

"We use a lot of water to grow crops. If things don't change, food security and access to clean water will be seriously threatened," said research team member Professor Jay Famiglietti from Arizona State University.

These changes “send one of the most serious messages about the impacts of climate change ever heard,” the authors say. Continents are drying up, freshwater is dwindling, and sea levels are rising.

The study, based on data from four NASA satellites that have tracked the movement of water across Earth over the past 22 years, including melting ice, groundwater and surface water, gives scientists a comprehensive view of the disrupted global water cycle.

Since 2014, already dry areas have gotten even drier. Several dry areas have coalesced into “megadroughts” that stretch from Central America, Mexico, California, western South America, to the Colorado River basin and the southern High Plains.

“The key message here is that water is the biggest driver of change both on land and in the oceans,” said Benjamin Hamlington, a scientist at NASA's Jet Propulsion Laboratory (JPL).

Agriculture will suffer serious consequences from unusual climate change - Photo: AI

How do drought and rising sea levels affect each other?

With the exception of Greenland and Antarctica, all of the world's major continents are experiencing unprecedented drought conditions since 2002.

Three-quarters of the world’s population lives in countries with rapidly depleting freshwater resources, according to research. Meanwhile, rising sea levels threaten to encroach further into coastal areas, reducing habitability and increasing the risk of flooding and severe storms. In the United States, extreme weather events are causing insurance companies to withdraw from many coastal cities because the risks are too great.

Drought and sea level rise may seem like two opposing climate phenomena: one is water shortage, the other is rising water causing flooding. However, scientists have shown that they can actually influence each other, especially in the current climate change.

In coastal areas like California, research shows that during droughts, sea levels can rise higher than normal. This is because less freshwater flows from the land into the ocean, allowing saltwater from the ocean to penetrate further inland. At the same time, increased evaporation during hot, dry conditions can cause sea levels to rise slightly due to changes in atmospheric pressure and hydrological circulation.

Conversely, as sea levels rise, saltwater can seep into aquifers and rivers in coastal areas, causing salinization of freshwater supplies. This makes it harder for soil to retain moisture and for plants to absorb water, exacerbating drought conditions, especially in places that rely on freshwater from rivers and groundwater.

In other words, droughts can cause seawater to intrude further, while rising sea levels can exacerbate water shortages. This vicious cycle is exposing coastal areas to a double whammy of climate risks, from prolonged drought to saltwater intrusion and water insecurity.

From a scientific perspective, drought and sea level rise are two manifestations of changes in the global energy balance and water cycle. As the climate warms, evaporation from land and ocean increases, causing a lack of moisture on land (drought) while at the same time melting polar ice and thermal expansion of ocean water, causing water levels to rise.

Droughts reduce the amount of freshwater flowing from rivers to the sea, changing salinity and sea surface temperature, two important factors that drive ocean currents. These changes can in turn affect seasonal rainfall, creating a destabilizing climate feedback loop.

In addition, saltwater intrusion caused by rising sea levels also disrupts the structure of underground aquifers, which are the main source of water during the dry season. Once these aquifers are saline, their ability to recover will be very slow, making subsequent droughts more severe.

Scientists say the link between rising sea levels and water loss from land is a sign that the natural water cycle is being seriously disrupted.

When water is sucked away from the continents, the only place it can go is the ocean. About 88% of the water vapor in the atmosphere eventually falls and flows into the sea.

Keeping a close eye on how much water is stored on land is vital. If we know where the water is going, we can improve our forecasts of future droughts, floods and water supplies.

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MINH HAI

Source: https://tuoitre.vn/nghich-ly-khi-hau-dat-cang-kho-han-bien-dang-cang-nhanh-2025072710044955.htm