NWC REU 2015
May 26 - July 31



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Projecting Future Change in Growing Degree Days of Winter Wheat

Natalie Ruiz-Castillo, Carlos Gaitan Ospina, and Renee McPherson


What is already known:

  • Winter wheat in Southwest Oklahoma is important because this is one of the most productive regions for growing this highly consumed crop.
  • Winter wheat can serve as a forage, grain or dual purpose crop.
  • Growing degree days (GDD) are very useful in measuring plant development.
  • Statistically downscaled Global Climate Models (GCM) have been used in climate change impacts studies.

What this study adds:

  • By using new statistically downscaled outputs and focusing on this subset of the Red River Basin, a more detailed look at the accumulation of growing degree days for winter wheat is provided.
  • This provides historical and future change in mean GDD for Southwest Oklahoma.
  • We identified that the main source of uncertainty in GDD outputs was the type of GCM used.


Southwest Oklahoma is one of the most productive regions in the Great Plains where winter wheat is produced. To assess the effect of climate change on the growing degree days (GDD) available for winter wheat production, we selected from the CMIP5 archive, two of the best performing Global Climate Models (GCMs) for the region (MIROC5 and CCSM4) to project the future change in GDD under the Representative Concentration Pathway (RCP) 8.5 — a "business as usual" future trajectory for greenhouse gas concentrations. Two quantile mapping downscaling methods were applied to both GCMs to obtain local scale projections. The downscaled outputs were applied to a GDD formula to show the GDD changes between the historical period (1961–2004) and the future period (2006–2098) in terms of mean differences. The results show that at the end of the 2098 growing season, the increase in GDD is expected to be between -2.0 and 6. Also, depending on the GCM used, Southwest Oklahoma is expected to see an increase in future GDD under the CCSM4 GCM and a mix of increase, no change and decrease under the MIROC5 GCM.

Full Paper [PDF]