Earth's biggest storms are about to get even more intense

A new global climate modeling project suggests that the heaviest rainstorms on land could become dramatically more intense this century.

Using far sharper detail than past tools, it warns that dangerous downpours may strike some regions much more often than expected.

The work, led by Dr. Ping Chang, an oceanographer at Texas A&M University, centers on MESACLIP, a set of computer experiments that simulate Earth from 1900 to 2100 at near weather-forecast detail.

Instead of boxes about 60 miles wide that many older models use, it divides the atmosphere into chunks closer to 15 miles across.

High resolution reshapes climate insight

Climate models – computer programs that simulate air, water, ice, and land physics – help scientists estimate future temperatures and rainfall. 

To stay affordable on the fastest supercomputers, many of these models chop the planet into coarse squares and move forward in large time steps.

Events with extreme precipitation, very intense rainfall that falls on only a few days each year, react strongly to details inside each grid box.

Studies have found that heavy downpours have become more common across many regions.

A new scale of detail

MESACLIP uses atmosphere boxes about 15.5 miles (25 kilometers) wide and ocean boxes near 6 miles (10 kilometers), which is very small for a global model. 

This high-resolution climate model, a climate model that uses smaller grid boxes than usual, allows storms and currents to organize more realistically.

The team ran the system from 1900 to 2100 under several greenhouse gas pathways. For some pathways it repeated the experiment ten times with small shifts in conditions, creating an ensemble forecast, a set of model runs that sample natural swings.

Altogether MESACLIP produced about 4,500 simulated years of climate, which took roughly 900 days on top-tier supercomputers.

Those runs generated around 6 petabytes of output, enough data that other teams will be mining for new results for many years.

Seeing storms that old models miss

Many earlier studies emphasized that warmer air holds more water, so more heat should mean heavier rain.

The new work highlights mesoscale moisture convergence, winds on regional scales that squeeze moist air together, as a second strong driver of future extremes.

These converging winds help feed mesoscale convective systems, large clusters of thunderstorms that last for hours and produce heavy rain. 

Studies suggest these systems produce extreme rainfall in many regions. MESACLIP also resolves hurricanes and atmospheric rivers, long bands of moist air that flow from ocean to land and can produce multi-day deluges. 

Because the model can see the structure of these features, it can better link extreme storms to broader patterns in winds and ocean temperatures.

Importantly the model reproduces both past global temperature changes and many observed heavy rain events more accurately than many coarser models. 

Wetter climate extremes

In a future where carbon pollution keeps rising strongly, the MESACLIP simulations project much heavier daily extreme rainfall over land. 

Under that high-emissions path, they find that daily rainfall extremes over land increase by 41 percent by 2100. 

Warmer air and oceans supply more water vapor, but MESACLIP shows that is only part of the story. In the fine-grid model, shifts in winds that focus moisture explain the extreme rain increase, so traditional models understate that dynamical push.

“It’s becoming clear now that the [traditional] models are not producing the true impacts of climate change,” said Dr. Doug Smith of the U.K. Met Office.

For regions like the United States Gulf Coast and coastal California, the high-resolution runs show extreme days appearing more often than models suggested. 

The simulations produce long chains of severe thunderstorms that march inland along preferred wind corridors, features that coarse grids simply could not represent.

Surprising climate twists appear

MESACLIP also reproduces an unexpected patch of recent cooling in the Southern Ocean and eastern Pacific, a feature that has puzzled scientists for years. 

In the simulations this cooling links to ozone hole above Antarctica, which strengthens winds over the Southern Ocean and drives upwelling of colder water.

The model captures Arctic warming partly because it represents warm water flowing through the Bering Strait from the Pacific into the basin. 

It suggests that the Atlantic Meridional Overturning Circulation (AMOC), a system of Atlantic currents that carries heat northward, weakens but does not collapse by 2100.

Experts want more models that resolve these intense systems directly instead of smoothing them over.

“I think we have to go for this kind of scale,” said Dr. Davide Faranda, a climate scientist at the Pierre Simon Laplace Institute.

The shift to sharper climate models

MESACLIP is part of a larger shift, as modeling centers worldwide develop similar fine-grid experiments for comparison. 

The High-Resolution Model Intercomparison Project (HighResMIP), run by a climate program, is pushing groups to run such experiments under a shared protocol for comparison.

Independent checks show that high resolution models can better match observed short bursts of intense rain than older coarse models. 

One detailed evaluation found that pushing grid spacing down toward a few miles reduced major errors in simulated extreme downpours.

New global experiments that track mesoscale convective systems directly back this up. These organized storms are expected to become more frequent and more intense in many regions as the planet warms.

Next-gen tools improve forecasts

As data accumulate, methods that use machine learning, computer algorithms that find patterns in datasets, will rely on simulations of extreme events for training. 

High-resolution ensembles like MESACLIP give those methods future-focused examples instead of only past records from a cooler world.

Put together, MESACLIP and related efforts show that when we improve our view of storms, the future looks stormier in many places but clearer.

With maps of where intense rain is expected to fall, communities can plan defenses, drainage, and warnings that match the climate they are heading toward.

The study is published in the journal Nature Geoscience.

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