Figure 1. U.S. Drought Monitor (March 13, 2018).
Current Drought Conditions
The recently released United States Drought Monitor map (Figure 1) indicates that Western and Central South Dakota still remain in severe drought conditions to abnormally dry conditions (Figure 2). With grazing season just around the corner, ranchers in Central and Western South Dakota need to start re-visiting their drought management plans and making adjustments if needed.
Figure 2. U.S. Drought Monitor for South Dakota (March 13, 2018).
South Dakota Drought Tool
The South Dakota Drought Tool is an excellent place to start if your ranch does not have a drought plan in place. The drought tool is an easy to use tool that gives a ranch manager an estimate of precipitation records and projected forage production for the area of South Dakota their ranch is located. If a ranch has its own precipitation records, a manager can input those precipitation records into the drought tool for a more accurate assessment for their ranch.
Previous Growing Season
The first trigger date is based on growing conditions from the previous year. For example, much of Western South Dakota was experiencing drought conditions last year, therefore average precipitation will not be enough to recharge soil moisture this year. Above normal rainfall will be needed to bring that soil moisture back to normal. So many ranchers affected by drought last year are already implementing management actions for this year such as adjusting stocking rates and culling cows. For some ranchers in Central South Dakota that had normal precipitation last year, they need to keep a very close eye on precipitation and grass conditions for the rest of this spring. They also need to have a drought management action plan in place if dry conditions persist and a reduction in livestock numbers is needed.
The second important trigger date is around April 15. Up to this date we can assess how much dormant season moisture we received from October –March and we can assess the precipitation forecast estimates for the rest of the spring. As stated by Roger Gates former SDSU Rangeland Specialist, “In the Northern Plains, where rangelands are dominated by cool-season grasses, spring precipitation (April, May, June) is the best single predictor of vegetation production for the entire growing season.” “By mid-April climate prediction models for spring rainfall are correct more often than not.” “If rainfall forecast predictions are below normal for the next 3 months reductions in livestock numbers should be made.” So ranches that had normal precipitation last year, they need to start thinking about how they can reduce their livestock numbers and have a plan in place if the precipitation outlook for the rest of this spring is below normal.
Roughly May 15 is another trigger date to pay close attention too. If precipitation conditions are still dry by May 15, it becomes increasingly difficult to get enough precipitation to maintain average soil moisture for the remainder of the growing season. Further reduction in livestock numbers may need to happen.
Reassessment of precipitation and moisture conditions should be done again around June 15. If dry conditions are persisting, more management actions will need to be implemented. By July 1, 75% to 90% of vegetation growth has been completed (Gates).
Figure 3. Example critical date and action flow plan.
As many ranches across South Dakota are in the middle of calving season, the next 3 months are a critical period for precipitation and grassland production in South Dakota. Areas of South Dakota that were not in drought conditions last year but are experiencing dry conditions right now need to pay close attention to precipitation and grass conditions and make sure a drought plan with management actions is in place to reduce stocking rates if dry conditions persist. For ranches that were in a drought last year or the last 2 or 3 years, continue with management actions that were taken last year and make necessary adjustments to this year’s drought plan if dry conditions persist.