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More Than Half the Lower 48 Is in Drought Right Now, and the Clay Under Your Slab Is Shrinking

By Call The Local Editorial16 min read
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More Than Half the Lower 48 Is in Drought Right Now, and the Clay Under Your Slab Is Shrinking

The number to start with is 52.70%. That is the share of the Lower 48 sitting in drought (D1 through D4) as of the August 18, 2026 U.S. Drought Monitor national summary. Counting the U.S. and Puerto Rico together, it is 44.34%. Roughly 93.1 million people live inside those boundaries, and 42 states show moderate drought or worse.

Most coverage of a number like that goes straight to lawns, reservoirs, and crop yields. Fair enough. But there is a second map hiding inside the drought map, and it matters more to your house than your grass does. Across a wide band of the country, the dirt your foundation rests on is not inert fill. It is clay that swells when it is wet and shrinks when it is dry, and it does both with enough force to move a building. When drought pulls water out of that clay, the soil contracts and quietly withdraws support from the slab or footings above it.

If you live in the Texas Blackland Prairie, the Gulf Coast, western Oklahoma, the Carolinas Piedmont, or the Colorado Front Range, a drought map is also a foundation map.

What actually changed this week

It is worth being precise here, because the regional picture is less uniform than the headline percentage suggests. The Drought Monitor summary for the August 18, 2026 map, authored by David Mocko (SSAI/NASA/GSFC) and Curtis Riganti of the National Drought Mitigation Center, describes broad degradation in two regions and a mixed bag everywhere else.

  • The South got worse across the board. Per the authors, all states saw declining drought conditions under "anomalously warm temperatures and almost no precipitation." Only eastern Tennessee improved. Extreme and exceptional drought (D3 to D4) remains entrenched in western Oklahoma, the Texas Panhandle, and southeastern Arkansas.

  • The West degraded too, in small to moderate steps across California, Oregon, Washington, Nevada, and northern Utah, with exceptional drought holding in northeastern Oregon and far southern Idaho. Southern Utah and Arizona improved slightly on monsoon activity.

  • The High Plains and Midwest mostly improved. Eastern Colorado, Wyoming, and Nebraska picked up welcome rainfall, and abnormally dry areas were removed entirely from Indiana, Ohio, and Kentucky. Degradation was confined to pockets: North Dakota, Michigan, Wisconsin, and southern Missouri.

  • The Northeast was mixed. Northern Maine, New Hampshire, and Vermont slipped, while upstate New York, Massachusetts, Maryland, Pennsylvania, and West Virginia improved on significant rain.

So the accurate summary is broad degradation across the South and the West, with pocket degradations in North Dakota, the Upper Midwest, and northern New England. If you are in Ohio or upstate New York, this week was good news. If you are in Texas, Oklahoma, or Arkansas, it was not.

Why a flash drought is harder on a slab than a slow one

Not all droughts stress a foundation the same way. NOAA's NIDIS program defines flash drought as rapid onset or intensification driven not by rainfall deficit alone, but by low precipitation combined with abnormally high temperatures, high winds, and radiation changes. Those extras spike evapotranspiration, which is the combined loss of water from soil surfaces and plants. The result is that soil moisture is stripped in weeks rather than over a season.

"Anomalously warm temperatures and almost no precipitation" is the textbook signature. And that speed is exactly the problem for a structure. Clay that dries gradually over many months lets a building settle in small increments it can often absorb. Clay that dries hard and fast pulls support away faster than the concrete above it can redistribute load, and concrete relieves stress the only way it knows how, which is by cracking.

The Intermountain West shows how extreme the heat side of this has been. A NIDIS status update dated August 20, 2026 reports roughly 95% of Arizona, Colorado, New Mexico, Utah, and Wyoming in drought, with about 30% in D3 to D4. January through July 2026 was the warmest on record for nearly every county in the region, and July was the warmest on record for Wyoming.

The physics, in homeowner terms

The clay minerals that cause trouble are smectites, and montmorillonite is the one you will hear named most often. They have a layered structure that takes water molecules in between the layers. Add water and the mineral physically expands. Take water away and it contracts. Ordinary sand and silt do not do this in any meaningful way. Smectite clay does it dramatically.

Consider the Texas state soil, Houston Black. Its NRCS Official Series Description classifies it as fine, smectitic, thermic Udic Haplusterts, with clay content running 40 to 60%. When it dries, the surface develops cracks 0.5 to 4 inches wide extending 12 inches or more deep, and in most years those cracks stay open 90 to 150 cumulative days. That is a formal soil-survey observation, not a worst case. Below the surface, the series shows distinct pedogenic slickensides at 61 cm and deeper, which are polished shear surfaces created by the soil grinding against itself as it swells and shrinks. The ground surface itself often shows gilgai microrelief, a subtle mound-and-swale pattern cycling every 10 to 24 feet with 8 to 46 cm of amplitude.

Now put a slab on top of that. Through a wet spring, the clay swelled and lifted. Through a hot, rainless August, the perimeter dries first, because the edges of the slab are exposed to sun, wind, and thirsty landscaping while the center stays insulated by the house. The soil contracts at the edges and the perimeter loses bearing support unevenly. That is why drought-related damage shows up first at the weakest points in the structure above, which are the openings: doors, windows, and corners.

The USGS mapped the national footprint of this problem decades ago in Swelling Clays Map of the Conterminous United States (Olive, Chleborad, Frahme, Schlocker, Schneider, and Schuster, 1989, I-MAP 1940, DOI 10.3133/i1940). It is still the canonical federal reference for where in the country this applies.

Your photo checklist for this month

This is the part to actually do, and it takes about twenty minutes. Walk the house inside and out with your phone and look for:

  • New or widening diagonal cracks above door and window corners. Openings concentrate stress, so they crack first.

  • Doors and windows that suddenly will not latch, or that stick in a way they did not in June. A door that swings open on its own is telling you the frame is out of square.

  • Gaps between crown molding and the ceiling, or between baseboard and floor.

  • Stair-step cracks in brick mortar joints on the exterior, following the mortar rather than cutting through brick.

  • Floors that slope or feel bouncy, and tile or grout lines that have started to crack in a line.

  • Separation at the garage door frame, which is a large opening in a wall with little to brace it.

Two habits make these photos worth ten times more later. First, date-stamp them, or at least keep them in a dated folder. Second, put a pencil mark and today's date at each end of every crack you find. If you repeat that in October and the crack has grown past the mark, you have documented movement instead of guessing about it. An engineer, an insurance adjuster, and a future buyer will all care about that record.

Regional soil notes

Texas Gulf Coast and the Blackland Prairie

Gulf Coast Vertisols and the Blackland Prairie soils of MLRAs 86A and 86B in north and east central Texas are the most reactive residential soils in the country. Houston Black and its relatives run 40 to 60% clay and crack the way the NRCS description spells out above. Combine that with the South's current warm and dry pattern and the Panhandle's D3 to D4 conditions, and Texas is where you would expect the highest volume of new foundation complaints this fall.

Oklahoma

Western Oklahoma is carrying D3 to D4 right now, per the August 18 map. That is the second consecutive layer of stress on soils that were already dry, and areas that never fully recharged over the spring have less moisture reserve to lose before the clay starts contracting.

The Carolinas and Virginia Piedmont

People are often surprised the Piedmont belongs on this list. It does. The Iredell series, weathered from diabase, diorite, and gabbro across SC, NC, VA, GA, and AL in MLRA 136, is classified as fine, mixed, active, thermic Oxyaquic Vertic Hapludalfs. Linear extensibility totals 6.0 cm or more between the surface and the paralithic contact, and the Bt horizon is rated VERY HIGH for shrink-swell. Permeability runs 0.0015 to 0.06 inches per hour, which is close to impermeable, so rain sheets across the surface rather than soaking in. That combination is rough: the soil shrinks hard in drought, then refuses to rewet quickly when rain finally arrives.

The North Carolina Geological Survey lists expansive soils as a named geologic hazard and notes they can occur anywhere in the Mountain, Piedmont, or Coastal Plain, with the greatest potential in the Carolina terrane and the Triassic Basins. Their framing is the clearest short version of the whole problem: swelling heaves foundations upward, shrinking pulls soil away and causes uneven settlement, and both produce cracked walls, foundation cracks, uneven floors, and broken utility lines.

The Colorado Front Range

The Colorado Geological Survey calls expansive soil the state's most damaging geologic hazard, responsible for more property damage than tornadoes, floods, earthquakes, and hurricanes combined. The mechanism there is bentonite and montmorillonite, which can expand up to 20% by volume and exert uplift forces up to 30,000 pounds per square foot. For context, engineers treat volume increases of 3% or more as potentially damaging. About half of the roughly 30 sedimentary bedrock formations exposed in the Front Range Urban Corridor, which runs from Fort Collins and Greeley down to Pueblo and Cañon City and holds more than 80% of Colorado's population, contain swelling clay.

Colorado homeowners have an unusually good free resource in the CGS consumer publication SP-43, A Guide to Swelling Soil for Colorado Homebuyers and Homeowners, with companion titles SP-14 on landscaping and maintenance on swelling soil and EG-07 on potentially swelling soil and rock in the Front Range Urban Corridor.

The money reality, and it is not friendly

Here is where a lot of homeowners get an unpleasant surprise. Standard homeowners policies generally exclude earth movement, and they separately exclude gradual settling, shrinking, and expansion. Drought-driven soil movement lands squarely in both buckets, because insurers treat it as gradual and foreseeable rather than a sudden accidental loss.

The Texas Department of Insurance home insurance guide is unusually blunt about this. It states that most policies do not cover damage from earthquakes or earth movement, and it lists "damage to foundations or slabs" among optional endorsements. In plain terms, in Texas foundation coverage is something you buy in advance, not something you discover you had after the crack appears. Check your declarations page now, not in November.

There is one real exception worth understanding. Damage caused by a sudden covered peril, such as a burst supply line or an accidental water discharge that erodes soil under the slab, can be covered even where soil-movement damage is not. That distinction is why plumbing hydrostatic testing matters. If a leak under the slab is the actual cause, testing establishes it, and the claim changes character entirely. If you are heading toward a claim, get the hydrostatic test before you file, not after.

What repairs cost

These are bands, not quotes. Costs vary a lot by region, access, soil, and how much of the perimeter is affected. Per HomeAdvisor's 2026 foundation repair cost data (an aggregator of reported project costs, not a primary source):

  • Cosmetic crack repair: $250 to $800

  • Slab jacking / mudjacking: $500 to $1,300

  • Piering or underpinning: $1,000 to $3,000 per pier, and whole-house jobs use a lot of piers, which is how these land in five figures

  • National average job: $5,175, with a typical range of $2,225 to $8,133

  • Severe cases: up to roughly $16,000

  • Structural engineer inspection: $340 to $780

That last line is the most important number in this article, and it is the smallest one.

How to tell a real engineer's report from a sales call

A licensed professional engineer sells you a report. A repair contractor sells you piers. Both may be perfectly honest, but only one of them gets paid the same amount whether your house needs work or not. When a repair company advertises a "free inspection," understand what it is: a sales call performed by someone whose revenue depends on the recommendation.

Paying $340 to $780 for an independent evaluation ahead of a potential $15,000 decision is the cheapest money in this entire process. Ask for a PE who does not also hold the repair contract.

What should a real evaluation contain? The Foundation Performance Association, a Texas nonprofit, publishes the reference standards on this in its committee papers index. The key document is FPA-SC-13-1, "Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings" (April 11, 2015, with a September 28, 2022 errata sheet). Practically speaking, look for a floor-elevation survey with actual measurements, a clearly stated level of investigation, and specific findings tied to observed conditions rather than generic language. Two other FPA papers are worth knowing about: FPA-RC-01-0 (2004) catalogs why foundation repair systems fail after installation, which is a useful reality check on any lifetime warranty pitch, and FPA-SC-18-0 (2014) covers standard of care for engineers working in Texas.

Prevention is cheap, boring, and works

The whole goal is stable soil moisture. Not wet, not bone dry, just consistent. Nothing here is expensive.

  • Soaker or drip line around the perimeter, placed roughly 8 to 18 inches out from the slab rather than pressed against it. Run it on a consistent schedule instead of sporadically. Because clay accepts water very slowly, use short repeated "cycle and soak" runs rather than one long soak that mostly runs off.

  • Never saturate. Re-wetting bone-dry clay too fast can drive heave and cause its own cracking. If your soil is already deeply cracked, ease back into watering gradually.

  • Downspout extensions carrying roof water 4 to 6 feet away from the house. This is a $15 fix that prevents a soaked spot right where you least want one.

  • Grade sloping away from the foundation so surface water leaves rather than pools.

  • Root barriers for thirsty trees. Mature willow, silver maple, oak, and elm can dewater clay well past their canopy dripline during a flash drought. A vertical root barrier between the tree and the foundation is the standard mitigation. And be careful with the obvious-seeming fix: removing a large tree near a slab can itself trigger heave as the soil rehydrates over the following seasons.

What is next

This is not a one-week story. The NOAA Climate Prediction Center Seasonal Drought Outlook valid for August through October 2026 favors drought persistence across southern Texas and the High Plains, anticipates development in the Northern Plains, and expects improvement across the Southeast. If you are in the persistence zone, the clay under your house has more drying ahead of it.

One closing point that catches people off guard. Foundation damage from drought often does not become visible during the drought. It shows up on the swell side, after the rain returns and the clay expands again, lifting unevenly against a structure that has already settled into a new shape. So do not read a wet October as the all clear. Take the photos now, mark the cracks, get the watering routine going, and if the marks move, spend the $340 to $780 on someone whose only product is an honest answer.

Sources

Note: This article contains AI-assisted content and has been reviewed by our editorial team.

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