Droughts and floods seem to be absolute opposites, yet increasingly they are coming hand in hand.
To understand why soil so easily repels water when it needs it most, we have to understand that soil is a living thing. The soil is made up of lots of organic matter, like dead plants and animals — that’s the stuff we can see. But what we can’t see are all the miniscule microbes. The microbiome in the soil is the network of bacteria that sequester carbon, breakdown organic material, and turn atmospheric nitrogen into ammonia that plants can use.
The microbiome is essentially the tiny team that keeps our crops growing. We take care of the microbiome when we fertilize, rotate crops, and practice minimal tilling. But during a drought, the microbiome starts to die.
Many plants contain a waxy substance to protect them and help them heal. Dead plants are broken down into organic matter, but during a drought (or in a wildfire) the wax in the plants can’t be broken down naturally because of the absence of sufficient microbes. The microbes that would normally come to the rescue simply aren’t there to help, thus the wax remains, leaving the soil with a coating of that wax on the top.
This video, posted by Dr. Rob Thompson of the University of Reading in England, shows how wet, moist, and dry soil soak up water differently.
In this experiment Dr Rob Thompson of @UniRdg_Met shows just how long it takes water to soak into parched ground, illustrating why heavy rainfall after a #drought can be dangerous and might lead to flashfloods. @R0b1et @UniRdg_water pic.twitter.com/zbb3xLTXdK
— Uni of Reading (@UniofReading) August 10, 2022
So what do we know? The microbiome breaks down plants. In a drought, our plants and microbiome die. When our microbiome dies the waxy substances in plants can’t be broken down, so it coats the soil, causing it to repel water, or in other words, be hydrophobic.
Thinking about Thompson’s video of different lawns soaking up water (or lack thereof), it’s obvious that when our soil is hydrophobic, even a little bit of water can have a big impact.
After a drought, any amount of rain will cause flooding, which can be localized or it can cause severe flooding of major waterways. Water can pool in low land areas, much like how swamps and marshes hold water in the spring, but mostly dry up in the summer. But when the soil is hydrophobic and the water wants to run off, it finds its way to creeks and rivers or drainage pipes in streets.
If you take a look through images and video of the devastation in Hereford, Texas, you’ll notice most of the damaged areas are near the running water, such as Tierra Blanca Creek.
Floods are always worse when they follow a drought, and the more droughts we have, the more damage it does to the soil. There is little we can do to prevent droughts, as we can’t control the weather, but there are things we can do to help mitigate our risks of drought.
Since soil becomes hydrophobic because of dying microbes, we need to work hard to keep our microbes happy. Especially on smaller scales, if your soil becomes hydrophobic, try working manure into the top layer of soil and watch the microbes come back to life. By keeping the microbes happy, we are giving our soil a better chance at soaking up water during or after a drought.
Having cover crops on fields and not allowing it to stand without any vegetation is important, as plants will help the soil to soak up more water, and plant roots are taking up groundwater. Think about Thompson’s video of the dry vs. moist soil — if there’s vegetation there’s some water!
As the climate warms, it is more important than ever to keep our soil healthy and microbiome happy.
To learn more, check out this podcast by Wired featuring Hannah Cloke, a hydrologist at the University of Reading, or read this article from Australia’s Department of Primary Industries and Regional Development.
Elizabeth Maslyn is a born-and-raised dairy farmer from Upstate New York. Her passion for agriculture has driven her to share the stories of farmers with all consumers, and promote agriculture in everything she does. She works hard to increase food literacy in her community, and wants to share the stories of her local farmers.
