Oregon almonds and Louisiana oranges? It could be if future projections in hardiness zones come to fruition. A new study by University of Idaho researchers uses climate models to assess how the coldest temperature recorded each winter in the United States may change over the next several decades, and what these temperature changes might mean for horticulture.
The study, published in Environmental Research Letters, was funded by Regional Approaches to Climate Change, or REACCH, a U.S. Department of Agriculture National Institute of Food and Agriculture project led by UI.
The USDA uses multi-year averages of annual coldest temperature to assign cold hardiness zones. Growers use these zones to gauge which crops will survive in their area.
The UI researchers’ model predicts the annual coldest temperature will climb in coming years, as will overall average winter temperatures. Other studies have shown that average minimum temperatures have already been showing warming trends over the 20th century, but this new study shows extreme lows will rise faster. This will result in a widespread change in U.S. hardiness zones in response, said Lauren Parker, a doctoral candidate in geography in UI’s College of Science and the study’s lead author.
In some places, such as the Northern Plains, this shift will happen faster than in others, such as along the Pacific coast.
“When farmers are thinking about their long-term planting and management strategies, this would be something to keep in mind,” Parker said. “Our projections are for midcentury, so if you’re a young farmer just starting out, by the time you’re passing your farm along to the next generation, if not before, you may be seeing some of these changes.”
Warming of the annual coldest temperatures could allow for an expansion of areas suitable for growing high-value tree crops such as almonds and oranges that are currently limited by cold winter temperatures.
“Cold hardiness zones are linked to broader temperature patterns, and the warming of cold extremes and average minimum temperatures could mean new opportunities for growers,” Parker said. “If our favorite foods can be cultivated over a larger area, there may be more ability for stable food prices in years of regional drought, spring freeze or other events that impact crop yields.”
Co-author John Abatzoglou, an associate professor of geography at UI, added that this warming is not all good news, however.
“While warming might allow us to grow cold-intolerant species in new areas, the lack of cold temperatures may also exacerbate problems related to pests and invasive species,” Abatzoglou said.
Warming winter temperatures may allow for the over-winter survival of crops, Parker said, but there are many other factors, such as water availability and heat stress, that influence where crops can be cultivated. Ongoing work is seeking to address these factors to provide a better picture of how future climate may shift the geographic distribution of crops.