Science You Can Use: A labor of love: Supporting ranchers and range managers with the South Dakota Drought Tool

Photo Credit

USDA figure

The South Dakota Drought Tool depicting where forage production would be reduced within the State as of May 1, 2026. The tool can be used for current and future predicted status so private land ranchers and public land managers can make crucial decisions for stocking capacities on their land. 

For 25 years, ranchers in South Dakota have used the South Dakota Drought Tool to estimate forage productivity of grazing lands. This crucial information helps them gauge whether to increase or decrease their herd size the following year. Management agencies also use the South Dakota Drought Tool to determine forage productivity of the lands they manage to balance the needs of livestock and wildlife.
Stan Boltz, a regional soil health specialist with the Natural Resources Conservation Service (NRCS), developed the Drought Tool to fulfill an unmet need he observed when working with ranchers. 

“Stan was well-respected in understanding the producer’s needs,” explains Jackie Ott, a Research ecologist with the Forest Service Rocky Mountain Research Station based in Rapid City. “He came up with this tool after reading the literature and identifying what environmental factors influenced forage productivity. For example, he saw that precipitation from the past two years affected current year productivity but saw that last year’s precipitation would have a greater effect on that productivity than precipitation from two years ago.” 

The Math Behind Predicting Forage Productivity 

Although the South Dakota Drought Tool has been favorably received and demonstrated its validity through use, the science underlying the tool wasn’t documented. “We told Stan we need to get his brain in mathematical format so that people can understand what he developed,” Ott says.
She, along with Shannon Kay, a Statistician with Rocky Mountain Research Station, and Emily Helms Rohrer, the State Rangeland Management Specialist with the NRCS, worked with Boltz to describe the mathematical equations underlying the tool and validate its outputs against actual forage productivity totals. 

This work was not straightforward because the Drought Tool model consists of three sub-models that account for the east-to-west precipitation gradient that occurs across the State and has been revised over the years.. Through the validation process, the team improved the model by incorporating better estimates of long-term productivity based on soil types. “The model actually predicts what producers often observe,” Ott explains. The tool is very user focused. Rohrer says, “Ranchers can put in their own precipitation data to localize for their specific microclimate.” 

A Tool That Builds Cooperation 

Ott recalls Boltz being amazed upon seeing the mathematical equations that underline what he intuitively developed based upon his literature review. Boltz unexpectedly passed away before seeing the publication of South Dakota Drought Tool: Current Model and Validation, yet his work continues to have positive impacts beyond the ranching community. The use of the Drought Tool has improved cooperation between ranchers and wildlife managers when cattle and wildlife use the same landscape for forage. And it’s why agencies and organizations such as the South Dakota Game, Fish, and Parks and the Rocky Mountain Elk Foundation provided funding for Ott and the team to develop the Drought Tool publication. 

Ott describes Boltz’s development of the South Dakota Drought Tool as a labor of love. “Stan could have just consulted as needed when producers had questions, but he wanted to come up with a solution that explained things that producers were observing,” she says. “Developing this tool was going above and beyond what his job required.”