This year’s particularly dry spring drove a large part of the Midwest, including Missouri and Illinois, into drought.
The lack of moisture has far-reaching implications, including on agricultural production and water levels on the country's largest rivers.
“Rain is essential—it is where drought starts and ends,” said Illinois State Climatologist Trent Ford. “As we were going into drought from April through June, we just weren’t getting rain.”
The present situation highlights the complexity of exiting drought when a state or region can slip into it relatively easily, Ford said. Rainfall across parts of the Midwest in recent weeks is helpful, but it may not be enough to alleviate the dryness, he said.Different kinds of rain
One complicating factor is the changing climate, which is causing increasingly sporadic rain events that can drop inches of rain in only a few hours, said Jason Knouft, a biology professor at St. Louis University who studies the impacts of human activities on freshwater resources.
“Those seem to be more common than these long, soaking rains,” he said. “When we get these intense rainfall events, you’ve got a lot of water hitting the landscape really quickly.”
The Northeast—especially Vermont—and parts of western Kentucky both experienced intense rain events this month, which spurred significant flooding. The ground often is unable to absorb all the water that comes in these kinds of storms, Knouft said.
“When you dump a huge amount of water onto a surface, even if you’re dumping it onto soil, there’s only so much the soil can absorb,” he said.
The rest runs off, meaning a local watershed is capturing only a fraction of the rain that fell, Ford said. He points to the St. Louis region as an example, which is close to the anniversary of historic rainfall last year.
The nine inches that fell in late July helped propel last summer to rank as the sixth-wettest all time for St. Louis, though the region was quite dry beforehand, Ford explained.
“Hydrologically, when we think about the plant’s response to that, we get very dry conditions, then we get this big burst of rainfall,” he said. “The majority runs off. It’s down the Mississippi, down to the gulf. It’s gone. You don’t have that water in your soil to deal with.”What’s in the ground
Soil conditions also play an important role in an area coming out of drought and in providing resilience. But what’s growing in the ground isn’t always the best at capturing water, Knouft said.
“We’ve got these row crops that don’t have particularly deep roots,” he said. “So when the rain falls, there’s not as much stability in the soil, so the water is able to effectively disrupt the soil and get through the soil more quickly.”
When a field isn’t in active agricultural production, cover crops can help soils retain rainfall, Knouft said. Perennial crops aid too, because their roots are deeper and maintain the soil integrity, which in turn makes it easier to hold onto water, he added.
Various crops respond to drought differently. Corn and soybeans can bounce back from early season dryness if given some rain, though current forecasts have some worried about severe crop damage.
Other crops aren’t as resilient on an annual basis, Ford said.
“We’ve seen more widespread impacts to pasture and hay conditions, mainly because when it comes to hay and rye grasses and other things that make up pasture,” he said. “Their natural reaction to drought is to cut off above-ground biomass creation.”
Those lands may not return to productivity until next year, Ford added.
“It’s all relative to what we care about,” he said. “If we care about corn and beans, it may just be we need near-normal rainfall through August. If we care about reservoirs or groundwater reserves or the water table, then it may be a bit longer of that recovery.”Flow on the nation’s biggest rivers
This year’s drought is also raising concern about low flows on rivers, including the Mississippi and the Missouri.
“It’s really the third summer in a row where we’ve had some sort of classification of drought in the majority of the basin,” said Mike Welvaert, service coordination hydrologist for the North Central River Forecast Center. “Most of the reservoirs, lakes and some of the smaller rivers and such just don’t have that much water in them.”
Water is trickling out of those resources, but only the minimum to sustain river flows, Welvaert said. That’s been the case for weeks, he explained.
Already some states have issued water restrictions because of the prolonged dryness, Welvaert added.
“The fact that we’re so low, so early in the year,” Welvaert said, “that is where our concern lies.”
It comes ahead of the Mississippi River’s natural low point of the year in the fall.
“It’s not the rainfall-driest time of the year,” Ford said. “But it’s the lowest time for rivers because it’s the cumulative effect of all the evaporation that happened in the summertime and peoples’ summertime water use for irrigation and things like that.”
The drought conditions are affecting the Mississippi’s levels because there’s less overall water in the ground that contributes to the base flow in the river and its tributaries, Welvaert said.
In more normal springs and summers, precipitation falls frequently and percolates into the ground, sometimes deep into the soil, he explained. It can then return to the surface as a spring or another source of groundwater, Welvaert added.
“That’s how most of the rivers maintain their certain level of water even when it’s dry out,” he said. “They’re getting water from underground sources.”
But the dryness across the upper Midwest and Great Plains means the top layer of soil is soaking up rain when it does fall, Welvaert said.
“We just don’t have any additional water to send downstream even when it does rain,” he said. “The same thing is happening in the Missouri Basin.”
Both Welvaert and Ford stressed the Mississippi’s fate for this year isn’t sealed yet. The weather patterns can still shift and produce a string of thunderstorms that drop consistent rain across the entire basin, Welvaert said.
“We really need more prolonged rainfall, but we can keep it at bay if we get the right amount of rain in the right places at the right times,” Welvaert said. “We’re still hoping for some of that to happen.”
