This year's particularly dry spring has pushed much of the Midwest, including Missouri and Illinois, into drought.
Lack of moisture has far-reaching effects, among other things agricultural production and the water level in the country's largest rivers.
“Rain is essential – that's where the drought begins and ends,” said Illinois climatologist Trent Ford. “As we were going through a drought from April to June, it just wasn't raining.”
The current situation highlights the complexity of getting out of drought when a state or region can slip into it relatively easily, Ford said. Rainfall in parts of the Midwest in recent weeks is helpful, but may not be enough to alleviate the dryness, he said.
Different types of rain
A complicating factor is the changing climate, which is causing more and more sporadic showers that can drop inches of rain in just a few hourssaid Jason Knouft, a biology professor at St. Louis University who studies the effects of human activities on freshwater resources.
“These seem to be more common than these heavy rains,” he said. “When we get these heavy rains, you have a lot of water hitting the landscape very quickly.”
The Northeast – especially Vermont – and parts of western Kentucky experienced heavy rainfall this month, which caused significant flooding. The soil is often unable to absorb all the water that comes in these types of storms, Knouft said.
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“When you put a huge amount of water on a surface, even if you dump it on the ground, the soil can only absorb so much,” he said.
The rest is runoff, meaning a local watershed only captures a fraction of the rain that fell, Ford said. He points to the St. Louis area as an example, which is close to its anniversary historic rainfall last year.
The nine inches that fell in late July helped last summer rank as the sixth-wettest on record for St. Louis, although the region was fairly dry beforehand, Ford explained.
“Hydrologically, when we think about the plant's response to this, we have very dry conditions, then we have this big burst of rainfall,” he said. “The majority are running. It's down the Mississippi, down in the gulf. Left. You don't have that water in your soil to deal with.”
What's on the ground?
Soil conditions also play an important role in an area emerging from drought and in providing resilience. But what grows in the ground isn't always the best at capturing water, Knouft said.
“We have these row crops that don't have particularly deep roots,” he said. “So when it rains, there's not as much stability in the soil, so the water is able to effectively disrupt the soil and move through the soil more quickly.”
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When a field is not in active agricultural production, crops can help soils retain rainfall, Knouft said. Perennial crops also help because their roots are deeper and maintain soil integrity, which in turn facilitates water retention, he added.
Different crops react differently to drought. However, corn and soybeans can recover from early-season drought if they receive rain Current forecasts have some worried about severe crop damage.
Other crops are not as resilient on an annual basis, Ford said.
“We've seen more widespread impacts on pastures and hay conditions, mainly because when it comes to hay and rye grasses and other things that make up pastures,” he said. “Their natural response to drought is to stop making biomass from the soil.”
Those lands may not return to productivity until next year, Ford added.
“It's all about what we care about,” he said. “If we care about corn and beans, we might need near-normal rainfall by August. If we care about reservoirs or groundwater supplies or the aquifer, then it might take a little longer than that recovery.”
Flow in the nation's largest rivers
This year's drought is also causing concerns about low flows on rivers, including the Mississippi and Missouri.
“This is really the third summer in a row where we've had some sort of drought classification across the majority of the basin,” said Mike Welvaert, coordinating service hydrologist for the North Central River Forecast Center. “Most reservoirs, lakes and some of the smaller rivers and such just don't have that much water in them.”
Water flows from these resources, but only the minimum to maintain river flows, Welvaert said. This has been going on for weeks, he explained.
Already some states have issued water restrictions due to prolonged dryness, Welvaert added.
“The fact that we're this low, this early in the year,” Welvaert said, “that's where our concern lies.”
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Public Radio St. Louis
It comes before the Mississippi River's natural low point of the year in the fall.
“It's not the driest time of the year with the rainfall,” Ford said. “But it's the lowest time for the rivers because it's the cumulative effect of all the evaporation that happened in the summer and people's use of the water in the summer for irrigation and things like that.”
Drought conditions affect Mississippi levels because there is less total water in the ground contributing to the base flow of the river and its tributaries, Welvaert said.
In more normal springs and summers, precipitation falls frequently and seeps into the ground, sometimes deep into the ground, he explained. It can then return to the surface as a spring or other source of groundwater, Welvaert added.
“So most rivers maintain a certain water level even when they are dry,” he said. “They get water from underground springs.”
But dryness in the upper Midwest and Great Plains means the top layer of soil absorbs rain when it falls, Welvaert said.
“We just don't have extra water to send down even when it rains,” he said. “The same thing is happening in the Missouri Basin.”
Both Welvaert and Ford stressed that Mississippi's fate for this year has yet to be sealed. Weather patterns can still change and create a series of storms that drop steady rain across the 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 time,” Welvaert said. “We're still hoping for some of that to happen.”
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