Figure 1. S.D. Grasslands Current Projected Production for March 15, 2017.
Current Grassland Conditions
The South Dakota Natural Resources Conservation Service (NRCS) recently released two maps (Figure 1 & Figure 2) highlighting the current grass production estimates and projected peak grass production estimates for South Dakota. These maps updated monthly by the NRCS indicate dry conditions spreading east into areas of North-Central and South-Central South Dakota. Ranchers in Central and Western South Dakota need to start re-visiting their drought management plans and making adjustments if needed.
Figure 2. S.D. Grasslands Projected Peak Production by July 1, 2017.
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 (Figure 3). 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 lies on. If a ranch has its own precipitation records, a manager can input them into the drought tool for a more accurate assessment for their ranch.
Figure 3. South Dakota Drought Tool from NRCS.
Figure 4. Critical date and action flow plan.
First Trigger Date
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 (Figure 5), 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 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.
Second Trigger Date
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 Extension Rangeland Management 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 in areas with normal precipitation last year, 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.
Third Trigger Date
Roughly May 15 is another trigger date to pay close attention too. If 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 persist, more management actions will need to be implemented. By July 1, 75% to 90% of vegetation growth has been completed (Gates).
Figure 5. South Dakota Drought Tool Evaluation for Meade County, Maurine weather station on 3/29/2017.
The Big Picture
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. Areas in Central 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, continue with management actions taken at that time and make necessary adjustments to this year’s drought plan if dry conditions persist. To find climate prediction models with temperature and precipitation forecast estimates, please refer to the National Weather Service climate prediction website.
Reference: Gates, R. 2013. Developing Trigger Dates for Drought Contingencies. SDSU Extension, Brookings.