How deep does Oklahoma soil dry out during drought?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Research using Oklahoma Mesonet data puts the depth of seasonal soil moisture change, called the active zone, at about 0.5 to 4 meters (roughly 1.6 to 13 feet), depending on the soil and climate. In the severe 2022 drought, Mesonet sensors recorded critically dry soil down to at least 32 inches. Typical steel pier depths in Tulsa sit below most of that range.

What is the active zone?

Clay soil swells as it takes on water and shrinks as it dries. Near the surface, rain, heat and plants change soil moisture all year. Deeper down, moisture stays nearly constant. The active zone is the layer in between that goes through seasonal wet-dry change, and it is where most foundation movement starts. A full explanation is in shrink-swell and the active zone.

Engineers often track this with soil suction, a measure of how tightly dry soil holds onto water. Where suction stops changing with the seasons is the bottom of the active zone.

How deep is the active zone in Oklahoma?

An Oklahoma State University study combined field measurements from the Oklahoma Mesonet and the U.S. Department of Energy's Atmospheric Radiation Measurement network with modeling ¹. Its findings:

The wide range reflects how differently Oklahoma soils transmit moisture: the study identified the rate at which moisture moves through soil as the key control on how deep seasonal change reaches ¹.

How do cracks carry drying deeper?

When clay shrinks it cracks, and open cracks let air and heat reach soil far below the surface. NRCS Official Series Descriptions record this for Oklahoma-area clays:

• Durant (type location in Bryan County, Oklahoma): cracks more than 1 cm wide and 30 inches deep form during dry periods ⁴.
• Hollister (type location in Hardeman County, Texas): cracks more than 30 inches (76 cm) deep stay open 150 or more cumulative days in most years ⁵.

These cracks are one reason drought drying can extend below what normal seasons reach. See Durant and Hollister.

What do Mesonet drought records show?

D-levels come from the U.S. Drought Monitor: D2 is severe, D3 extreme and D4 exceptional drought. For year-by-year history, see drought and wet years, and for how to read live soil moisture, see Mesonet for foundation pros.

How do pier depths compare to the active zone?

Oklahoma steel push pier installation records show piers in Tulsa typically reaching 8 to 16 feet, with a median of about 12 feet ⁶. That is deeper than most of the 1.6 to 13 foot active zone range estimated for the state ¹⁶. A pier that stops at a shallow depth in late summer, when clay near the surface is at its driest and hardest, may be resting within the active zone rather than below it. See steel push piers and seasonal movement calendar.

Large trees near a house add their own drying of the clay; see trees and roots.

Related

• Shrink-swell and active zone
• Drought and wet years
• Drought and wet cycles
• Mesonet for foundation pros
• Perimeter drying settlement
• Trees and roots