An expanding number of frost-free days, longer periods of drought, and an increasing number of high-temperature stress days in the coming decade are among the challenges Nebraska agriculture could face due to climate change, according to a new University of Nebraska-Lincoln report.
In short, the report that evaluates information from the May 2013 National Climate Assessment says Nebraska agriculture faces a number of potential stress points it will need to mitigate.
The UNL report, “Understanding and Assessing Climate Change — Implications for Nebraska,” said climate disruptions to agriculture have “increased in the past 40 years and are projected to increase over the next 25 years.” The report declared there is a scientific consensus on climate change and its causes.
By mid-century and beyond, the report said, “These impacts will be increasingly negative on most crops and livestock.”
On Thursday, a number of co-authors of the report were part of a discussion panel as part of the Heuermann lecture series in Lincoln.
Deborah Bathke, assistant professor of practice in meteorology-climatology at UNL, said university experts are in a position to lead on issues of adaptation, to provide “a positive, solutions-oriented focus rather than a doom-and-gloom approach.”
“Many” agricultural regions will see declines in crop and livestock production from “increased stress due to weeds, diseases, insect pests, and other climate change induced stresses,” according to the report. UNL points to a need to continue expanding and innovating conservation measures to mitigate what will be expected “loss and degradation of critical agricultural soil and water assets due to increasing extremes in precipitation.”
A rising incidence of weather extremes, the report said, will have “increasingly negative impacts” on crops and livestock. “Agriculture has been able to adapt to recent changes in climate; however, increased innovation will be needed to ensure that the rate of adaptation of agriculture and the associated socioeconomic system can keep pace with climate change over the next 25 years,” the report stated.
FROST-FREE DAYS
Farmers in Nebraska and across the country already have seen an increase in the number of frost-free days, according to the report, or the number of days between the last spring frost and the first fall killing frost.
“The length of the frost-free season determines the types of indigenous and invasive vegetation and cultivated crops that can survive within a particular region,” the report said. “Research shows that the country as a whole has experienced an increase in the number of frost-free days. The report said the length of the frost-free season in Nebraska has increased from five to 25 days and on average by more than one week since 1895.
“For Nebraska, the plant-hardiness zones between 1990 and 2006 changed dramatically. In 1990, the state was divided, with the southern portion of the state in zone five and the northern half of the state in zone four. By 2006, the entire state was in zone five, with the exception of a small portion of the state along the border with Kansas that was in zone six.”
The report said a shift in those plant-hardiness zones in the Great Plains is having a “profound effect on agriculture and ecosystems across the United States, even without considering changes in precipitation.”
TEMPERATURE CHANGES
The trend in low temperatures is greater than the trend in high temperatures, though both show overall warming, according to UNL. “These trends are consistent with the changes experienced across the Plains states, which show a general warming that is highest in winter and spring and a greater warming for the nighttime lows than the daytime highs,” the report said.
Along with annual average temperature, precipitation varies “strongly” from year to year in Nebraska, the report stated. “Unlike temperature, however, there is no discernible trend in mean annual precipitation in Nebraska.”
The trends in precipitation in the state show the most pronounced change in spring, “with a general increase across the state.” Summer is trending toward slightly less precipitation, UNL said, while fall and winter “show essentially no trend.”
Projected temperature changes in Nebraska range from 4 to 5 degrees, to 8 to 9 degrees Fahrenheit by the last quarter of the twenty-first century, the report said. “Under both the lower and higher emissions scenarios, the projected number of high temperature stress days over 100 degrees Fahrenheit is expected to increase substantially,” UNL said. “For Nebraska specifically, the projected changes are for high temperature stress days to increase to 13 to 16 additional days for the lower emissions scenario and 22 to 25 days for the higher emissions scenario.”
During the Heuermann lecture this week, report co-author Don Wilhite, professor of applied climate science in the school of natural resources at Nebraska, said if climate projections are accurate, then the multiple days above 100 degrees experienced in Nebraska in 2012 “would be an average summer.”
PRECIPITATION TRENDS
Trends for increased precipitation in the northern Great Plains are projected to become even more pronounced. The southern Great Plains will continue to become drier by mid-century and later. “The greatest increases for the northern Great Plains states so far have been in North and South Dakota, eastern Montana, and most of eastern Nebraska.”
When it comes to snow cover, the report said a projected reduction in snow pack in the northern Rocky Mountains will pose a threat to Nebraska farmers.
“Flow in the Platte and Missouri rivers during the summer months critically depends on the slow release of water as the snowpack melts,” the report said. “Such flow could be greatly reduced in coming years.”
The report said the advent of large-scale irrigation in Nebraska “has kept the summertime climate in Nebraska cooler and wetter than it otherwise would have been. “However, if reduced water availability curtails irrigation in the state, then the microclimatic effects of irrigation will be lessened in the future,” the report said.
