New Hampshire is getting wetter on paper and drier on the ground, and a new study from Dartmouth College helps explain why. Researchers Justin Mankin and Corey Lesk analyzed decades of global rainfall records and found that storms in much of the world, including the Northeast, are consolidating into bigger and less frequent bursts. The annual rainfall totals keep rising. The amount of that rain that actually soaks into the soil and replenishes groundwater does not, according to reporting in the New Hampshire Bulletin on the study.

For Granite Staters, that finding lands at a moment when wells run dry in the summer, brush fires flare in October, and the same towns get pummeled by flash floods after a single weekend of heavy storms. The Dartmouth team’s argument is that those two experiences are not contradictions. They are two faces of the same underlying climate trend.

What the study found

Mankin and Lesk used global rainfall data going back decades to map two things at once: how often it rains, and how hard it rains when it does. They were looking for the rhythm of storms, not just the volume of water in the bucket at the end of the year.

The pattern they uncovered is what they call rainfall consolidation. Across much of the planet, storms are getting more intense, and they are arriving in clusters separated by longer dry stretches. The total annual rainfall in many regions is going up, sometimes substantially. But the share of that rainfall that arrives in a few violent bursts is also going up. Long, soaking, steady rains, the kind that creep gently into the soil and slip down into aquifers, are giving way to atmospheric river-style downpours that hit the landscape hard and then leave.

There are exceptions. In far northern latitudes the data show the opposite trend, with rain events becoming more spread out rather than more clustered. But the Northeast, including New Hampshire, sits squarely in the consolidating pattern, said state climatologist Mary Stampone, who was not involved in the study.

The intuitive question is whether more rain just translates into more groundwater. The Dartmouth team’s answer is that it does not. Their study concludes that as rainstorms consolidate into more concentrated bursts, the long-term effect on the landscape is actually drying, not wetting. Project that pattern forward another 1 degree Celsius of warming, which the planet remains on track to see in coming decades, and the researchers calculate that many of the world’s regions could shift toward abnormally dry conditions overall.

“Here we uncover a new way in which a warmer world is a drier world,” Lesk said.

Why intense rain does not refill aquifers

If you have ever watched a hard rain bounce off a baked August driveway, you have already seen the physical mechanism the Dartmouth team is describing. When rain falls slowly over a long period, soil and vegetation have time to absorb it. Water trickles down through pore spaces, recharging shallow groundwater and ultimately percolating into the deeper aquifers that wells, springs, and many municipal water systems rely on.

When rain falls in extreme bursts, that absorption process gets overwhelmed. Water hits the ground faster than the soil can take it in. Excess pools on the surface, runs off into ditches and streams, swells rivers downstream, and then is gone. The atmosphere just delivered a year’s worth of water in a weekend, and the land kept only a fraction of it.

Mankin offered a homely metaphor in interviews about the findings: think of a pint glass. “If you have a pint glass, and you get a pint of water every day and you can use it, that’s one thing. But if you get two pints, and you have a pint glass, and it spills over and you have to wait two days to get your next refill, then you can see quickly how all that water at once is not useful to you.”

Stampone, the state climatologist, said her own field observations line up with what Mankin and Lesk are seeing in their global data. “What we’re seeing on the ground is what they’re demonstrating,” she said. New Hampshire’s annual precipitation has trended upward over the long term. So has the frequency of extreme single-day rainfall events. A Climate Central analysis cited in the Bulletin coverage shows how rainfall in Concord has shifted toward more intense events over time.

What it means for New Hampshire

The Granite State has been a case study in this paradox for years. Single storms can dump enough water to overwhelm dams. The July 2023 storms that contributed to the collapse of Forest Lake Dam in Winchester are still seared into local memory. But the very next summer can see well drillers running ragged in the seacoast and Lakes Region as private wells dry up, agricultural irrigation tightens, and brush fire risk creeps up in October.

This is not a hypothetical for the state’s water managers. Last year’s drought and wildfire conditions across New Hampshire’s forests pushed officials to revisit forest management and fuel-reduction strategies. Communities along the Merrimack and its tributaries continue to wrestle with the dual challenges of stormwater management and water-quality protection, including the ongoing fight over PFAS in the Manchester wastewater discharge that feeds the river relied on by hundreds of thousands of downstream residents.

The Dartmouth study suggests this whiplash is structural, not accidental. As Mankin put it, the climate is not simply asking the state to plan for wetter conditions or drier conditions. It is asking the state to plan for both at the same time. “It’s not as simple as the binary of wetter or drier, and kind of managing for that. What climate change asks society to do is manage both at the same time, and I think these results really exemplify that,” he said.

For state and local officials, that means infrastructure investments designed for the median storm of the past will be wrong in two directions at once. Culverts and bridges sized to handle ordinary storms will be undersized for the extreme events. Wells and reservoirs designed to draw down through long, gentle storm seasons will be left high and dry during the long gaps between bursts. Tools like the state’s home insurance grants and climate resilience program are early attempts to push some of those upgrades down to the level of individual homes and small communities, but the systemic problem is much larger.

Agriculture, in particular, is exposed. New Hampshire’s farms are small, often family-run, and frequently dependent on small surface ponds, shallow wells, and natural soil moisture. A wet year that delivers all its rain in three storms can be devastating for crops, leaving fields drowned in the spring, hard-baked by midsummer, and then drowned again at harvest. Maple producers, dairy operations, and orchards each have their own vulnerabilities to this pattern.

What can be done about it

The researchers were careful not to oversell a fix. The first step, they argue, is recognizing that more annual rainfall does not necessarily mean more available water. From there, planners can design for the new rhythm rather than the old one. That includes investments in stormwater capture, low-impact development, restored wetlands and floodplains that can slow water down and let it soak in, modernization of aging dams and culverts, and groundwater monitoring that catches drawdown problems before private wells fail.

Some of that work is already happening in New Hampshire. The Department of Environmental Services has expanded drought monitoring in recent years and added more groundwater observation wells. Conservation districts and watershed associations across the state have been working with landowners on practices that improve infiltration: rain gardens, vegetated buffers, cover cropping on farmland, and forest management approaches that protect headwaters. The Hubbard Brook Experimental Forest, recently the subject of a federal review that ultimately kept the long-running research site open, continues to feed the kind of long-term data that studies like the Dartmouth one depend on.

The Dartmouth study lands as a reminder that the simple story, more rain therefore more water, is not the story we are actually in. The harder story, more rain and yet less usable water, is going to require a more honest conversation about resilience, infrastructure, and how the state pays for both.

FAQ

If New Hampshire is getting more rain, why are we still having droughts?

The Dartmouth study found that storms in the Northeast are consolidating into more intense, less frequent bursts. That means the total annual rainfall is rising, but a larger share arrives in extreme events that run off rather than soaking in, while the gaps between storms get longer. The result is more annual rain and less reliable groundwater.

Who did the study?

The study was conducted by researchers at Dartmouth College, including Justin Mankin and Corey Lesk. They used decades of global rainfall data to track how the frequency and intensity of rainstorms have shifted in different regions, including the Northeast.

Does this apply only to the Northeast?

No. The researchers found rainfall consolidation across much of the planet, with some exceptions in far northern latitudes. The Northeast, including New Hampshire, is part of the broader consolidating pattern, according to state climatologist Mary Stampone.

What does this mean for homeowners with private wells?

Homeowners on private wells may see more frequent low-yield problems during dry stretches, especially in late summer and early fall, even after wet years. Conservation practices, smarter water use, and in some cases deeper or rehabilitated wells may become more important. Tracking groundwater levels through the state's monitoring program is a good early warning system.

Can New Hampshire do anything to fix this?

There is no single fix, but the study points to a long list of measures that can soften the impact: stormwater capture, restored wetlands and floodplains, larger and more resilient culverts and dams, expanded groundwater monitoring, and conservation practices on farms and forests. Many of those investments are already underway at the state and local level, but the pace of change is slower than the climate trend.

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