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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #372850

Research Project: Adaptive Grazing Management and Decision Support to Enhance Ecosystem Services in the Western Great Plains

Location: Rangeland Resources & Systems Research

Title: Seasonal grassland productivity forecast for the U.S. Great Plains using Grass-Cast

item HARTMAN, MELANNIE - Colorado State University
item PARTON, WILLIAM - Colorado State University
item Derner, Justin
item SCHULTE, DARIN - Colorado State University
item SMITH, WILLIAM - University Of Arizona
item Peck, Dannele
item DAY, KEN - Climate Variability Unit, Science Division Department Of Science, Information Technology And Innova
item Del Grosso, Stephen - Steve
item LUTZ, SUSAN - Colorado State University
item FUCHS, BRIAN - University Of Nebraska
item CHEN, MAOSI - Colorado State University
item GAO, WEI - Colorado State University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2020
Publication Date: 11/13/2020
Citation: Hartman, M.D., Parton, W.J., Derner, J.D., Schulte, D., Smith, W.K., Peck, D.E., Day, K.A., Del Grosso, S.J., Lutz, S., Fuchs, B., Chen, M., Gao, W. 2020. Seasonal grassland productivity forecast for the U.S. Great Plains using Grass-Cast. Ecosphere. 11(11). Article e03280.

Interpretive Summary: Predictions of the upcoming grazing season's grassland productivity have been requested by ranchers and land managers for the US Great Plains. We developed Grass-Cast (a grassland productivity forecast system) to provide science-informed estimates of growing season aboveground production. This system was developed with over 30 years of historical data (weather, remote sensing) and modeling of plant growth (via DayCent) and season precipitation forecasts to provide site-based and regional forecasts that can assist in land manager decision-making. Grass-Cast is available in April and updated every 2 weeks through July. These forecasts are currently available for the Great Plains, with expansion of this geographically to the US Southwest forthcoming. The website for Grass-Cast is

Technical Abstract: Every spring, ranchers in the drought-prone U.S. Great Plains face the same difficult challenge—trying to estimate how much grass will be available for livestock to graze during the upcoming summer grazing season. To reduce this uncertainty in predicting forage availability, we developed an innovative new grassland productivity forecast system, named Grass-Cast, to provide science-informed estimates of growing season aboveground net primary production (ANPP). Grass-Cast uses over 30 years of historical data including weather and the satellite-derived normalized vegetation difference index (NDVI)—combined with ecosystem modeling and seasonal precipitation forecasts—to predict if rangelands in individual counties are likely to produce below-normal, near-normal, or above-normal amounts of vegetation. Grass-Cast also provides a view of rangeland productivity in the broader region, to assist in larger-scale decision making —such as where grazing resources might be more plentiful if a rancher’s own region is at risk of drought. Grass-Cast is updated approximately every two weeks from April through July. Each Grass-Cast forecast provides three scenarios of ANPP for the upcoming growing season based on different precipitation outlooks. Near real-time 8-day NDVI can be used to supplement Grass-Cast in predicting cumulative growing season NDVI and ANPP starting in mid-April for the Southern Great Plains and mid-May to early June for the Central and Northern Great Plains. Here we present the scientific basis and methods for Grass-Cast along with the county-level production forecasts from 2017 and 2018 for ten states in the U.S. Great Plains. The correlation between early growing season forecasts and the end-of-growing season ANPP estimate is > 50% by late May or early June. In a retrospective evaluation we compared Grass-Cast end-of-growing-season ANPP results to an independent dataset and found that the two agreed 69% of the time over a 20-year period. Although some predictive tools exist for forecasting upcoming growing season conditions, none predict actual productivity for the entire Great Plains. The Grass-Cast system could be adapted to predict grassland ANPP outside of the Great Plains or to predict perennial biofuel grass production.