Every spring, ranchers face the same difficult challenge of trying to guess how much grass will be available for livestock to graze during the upcoming season.
Since May 2019, an innovative Grassland Productivity Forecast or “Grass-Cast” has been helping producers in the northern and southern Great Plains reduce this economically important source of uncertainty.
Officially launched this spring, Grass-Cast is now available to producers throughout New Mexico and Arizona.
This experimental grassland forecast is the result of collaborations between the U.S. Department of Agriculture’s Agricultural Research Service, Climate Hubs and Natural Resources Conservation Service; the National Drought Mitigation Center; Colorado State University and the University of Arizona.
Funding from USDA ARS and NRCS, as well as NDMC and the USGS has supported Grass-Cast’s expansion to the Southwest region.
Caiti Steele, associate professor at New Mexico State University College of Agricultural, Consumer and Environmental Sciences Jornada Experimental Range and coordinator of the USDA Southwest Climate Hub, is on the team helping to share information about Grass-Cast.
“Deciding appropriate stocking rates is one of the most critical decisions a rancher can make for maximizing livestock weight gain while maintaining rangeland productivity,” Steele said. “But often it’s difficult to translate seasonal weather outlooks for the growing season into forage production.”
Grass-Cast uses over 30 years of historical data about weather and vegetation growth – combined with seasonal precipitation forecasts – to predict if rangelands are likely to produce above-average, near-average, or below-average amounts of forage in the upcoming growing season relative to their area’s more than 30-year history.
“To be clear, Grass-Cast doesn’t predict if or how well new stands of grass will grow in a specific location,” Steele explained. “Grass-Cast instead gives a prediction of how well existing, established rangeland forage resources will perform if the growing season is wetter, dryer or near normal in terms of precipitation and evapotranspiration.”
Grass-Cast also gives ranchers a view of rangeland productivity in the broader region to help with larger-scale decision-making, such as determining where grazing resources might be more plentiful if their own region is at risk from drought.
Steele emphasizes that Grass-Cast maps are intended to complement other sources of information that ranchers rely on for their management decisions.
“Producers should not rely on Grass-Cast as a sole source of information,” she said. “Similarly, public land managers should not use Grass-Cast as a sole source of information for setting stocking rates, determining turnout dates, or for other aspects of lease agreements, allotments or permits.”
The first publicly available forecast for the Southwest was released in May 2020, specifically for the spring growing season, which ended on May 31.
Grass-Cast maps for the Southwest’s summer growing season were posted to the Grass-Cast website in mid-June and will be updated every two weeks. These maps provide productivity estimates for rangelands at the peak of the summer monsoon growing season of June 1 through September 30.
The early monsoon season maps do show a broad range of estimates in productivity because they are mostly based on seasonal precipitation outlooks, not measured precipitation, Steele explained.
“The NOAA Climate Prediction Center currently shows equal chances of above and below-normal precipitation,” she said. “So we have equal chances of the forage production levels estimated in the three Grass-Cast maps for the Southwest region right now.”
However, as the growing season unfolds, Grass-Cast includes more and more measured precipitation amounts and its accuracy improves. The grassland productivity forecasts are updated every two weeks to incorporate newly observed weather data and emerging trends in growing conditions, so it should be consulted more than just once during the growing season.
“Keeping checking the maps,” Steele said, “and let us know what you think.”
Visit the Grass-Cast website at grasscast.unl.edu for updates, the latest maps, and other resources.
Contact Steele at [email protected] for more information and a remote presentation on Grass-Cast and how it was developed.
For more information on Grass-Cast, contact Dannele Peck, director of the USDA Northern Plains Climate Hub, at [email protected].
Author: Jane Moorman – NMSU
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