You can call it climate change, or you can call it extreme variables in weather patterns. Whatever you want to call it, regardless of your beliefs, the numbers don't lie: In Nebraska, variability in weather events has become more frequent over the last 30 years.
However, the challenge with a state like Nebraska is the general variability in precipitation and climate from east to west means that the frequency of changing weather extremes is also highly variable from one part of the state to the other. In addition, it's important to note that trends over a 30-year period can vary dramatically from trends over a 100-year period.
Overall, Nebraska's average annual temperature is increasing — about 2 degree F per century — although that's mostly due to increases in minimum temperatures in winter, and mostly in western Nebraska, according to state National Oceanic and Atmospheric Administration data. Meanwhile, the frost-free period is happening later, but mostly in western Nebraska as well. The incidence of May freeze events since 2010 has doubled compared to the previous 10-year period.
"At least when it comes to winter temperatures, western Nebraska has increased at a faster rate since 1895," says Tyler Williams, Nebraska Extension educator. "It's generally been warming quite a bit earlier in western Nebraska. Even as you get into central Nebraska, you can see that trend. A lot of the warming has come in the latter part of the winter. Even from recent memory, February and March have generally been quite warm in western and central and southern Nebraska."
WETTER IN EAST: NOAA data shows an increased amount of variability in precipitation events in the eastern part of the state for the last 30 years. This data shows precipitation for east-central Nebraska from 1917 to 2017.
In the eastern part of the state, state climatologist Al Dutcher notes there has been a distinct cooling pattern in the spring. "The tendency we've seen has been that our springs overall cooling tendency is only one piece of the pie," says Dutcher. "If we break it down further, what has become prevalent recently is we're dominated by spring temperatures that are warmer than normal in March than get cooler than normal for the second half of the spring when we're getting into the field and planting."
With precipitation, it's a little more difficult to illustrate a consistent trend, adds Dutcher, since the nature of precipitation in Nebraska is variable. However, he says there has been an increase in variability in precipitation starting in the late 1970s to early 1980s, particularly in eastern Nebraska. "That came off of a long-sustained downtrend in variability for the previous 30-year period," says Dutcher. "Prior to that, we saw a significant increase in variability, which matches up for the period of the ’30s and the ’40s."
Williams notes there has been an increase in spring precipitation, especially in eastern Nebraska in April, coming off of an increasingly dry, warm March. But that has come at the expense of summer and fall precipitation — and the overall trend in precipitation has been fairly stable statewide.
However, precipitation and humidity play a role in recent temperature patterns. It takes more energy to warm and cool water than drier air. That's why the humid east sees much less diurnal temperature swings between day and night than the semi-arid west.
"Consequently in the summertime, with more precipitation and humidity, we've seen warmer nighttime temperatures," Williams says. "Especially in July, it won't get quite as cool at night, but not as hot during the day. A lot of times that coincides with humidity and soil moisture."
That's largely driven by the dominant pressure systems in the state, adds Dutcher. The western half of the state is primarily under the influence of a high-pressure ridge, while the eastern half is primarily under a low-pressure tropospheric trough — or an area of below-normal pressure in the upper atmosphere.
WARMING TREND: Overall, statewide NOAA data shows the average annual temperature in Nebraska is increasing by about 2 degrees F per century, mostly due to increases in minimum temperatures in winter, mainly in western Nebraska.
"Nebraska lies in the middle of the country and splits these two in half," says Dutcher. "The western half is more in line with what happens in the western U.S. in regards to temperatures, while the eastern is more consistent with what happens in the Hudson Bay region."
So, the variability in weather patterns in eastern Nebraska may not apply to western Nebraska, and this affects growers in different parts of the state in different ways. "The interplay of regional variability is an important play on understanding this climate change issue," Dutcher says.
In upcoming Resilient Ag Landscapes installments, look for additional information on what weather variability means for growers, and what growers can do to address it.