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The Iowa Gardener: Iowa’s changing weather
Iowa is getting warmer; entire state now falls into Zone 5
Here in the Midwest, we are no strangers to weird weather. It’s a drought one summer and floods the next. A subzero March day can be followed the next by a balmy 70 degrees. But across the globe, weather is getting overall warmer and more extreme and that includes in Iowa.
This warmer, wilder weather means that gardens will need to be smarter than ever with basic practices like plant selection and placement, watering, weed control, pests and diseases, mulching and soil improvement. Plants and techniques that worked decades ago will not work as well now and into the future.
According to Iowa State University Extension, Iowa is approaching 1.5 degrees warmer today than it was in 1988. This does not mean that every year is warmer than the previous one. There is a considerable variation between years, but overall the trend is up.
The U.S. Department of Agriculture has already recognized this climate change by revising its Plant Hardiness Zone Map. These are the zones you often see listed on plant labels, as in “Zone 4-7.” Back in the 1990s, roughly the northern half of Iowa was Zone 4 and the southern half was Zone 5. Now the whole state is Zone 5.
This small increase in temperature may not seem like much, but for the climate, it’s huge with tremendous repercussions. For comparison, consider the fact that the difference in Earth’s temperature between now and the ice age when glaciers covered much of Iowa is only 10 to 12 degrees.
ISU Extension reports that northwest Iowa has warmed the most and southeast Iowa the least. Minnesota, Wisconsin, Nebraska and Missouri have all warmed faster than Iowa.
Winters have warmed more than any other season. Our fall has warmed more than spring. Summers have essentially remained unchanged, but this is expected to change in the future. Also, nights have warmed faster than days.
Short term, this spring is likely to be warmer and wetter than normal, according to State Climatologist of Iowa Justin Glisan. That increases the likelihood of thunderstorms and heavier rainfalls. Short-term, this is welcome news since true to climate extremes, Linn County and Eastern Iowa still is experiencing extreme drought — one of the worst it has seen in 70 years.
Other information shared by ISU Extension includes:
- The Midwest is projected to see the largest future increases in temperatures in the United States, so Iowa’s temperatures will likely ramp up. Even now, we are seeing more of those long summer heat waves that were rare when older Iowans were young. Five out of every 10 years, a five-day heat wave now averages 90 to 95 degrees in central Iowa.
- By 2050 in Iowa, the average temperature is expected to climb even more — a whopping seven degrees to 97 to 102 degrees. Once every 10 years, temperature will spike 13 degrees higher, pushing the five-day heat wave to 103 to 108 degrees. Also, those weather extremes will increase, with day-to-day and season-to-season temperatures ricocheting all over the place.
- Iowa’s annual precipitation has increased since the 1900s. This is due in large part to warming waters in the Gulf of Mexico and the fact that warmer air can hold more moisture. Most of the wettest years on record have occurred since 1982. In the future, most of the increase in this precipitation will come from wetter springs, with drier or little change in summers. However, summer precipitation will become more variable with longer stretches between rains.
- The intensity of rain has also increased. Across the Midwest, very heavy rainfalls increased by 42 percent from 1958 to 2016. Iowa ranks fourth nationally in the number of floods since 1988. This increase in heavy rainfall events is expected to continue into the future.
Next, I’ll talk about how to garden in a time of climate change.
Veronica Lorson Fowler is co-publisher of the Iowa Gardener website at www.theiowagardener.com.
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