Drought again in the Southern Plains – what does it mean big picture?Drought again in the Southern Plains – what does it mean big picture?
Just because our data do not show an intense drought, it doesn’t necessarily mean there aren’t impacts being experienced.
May 31, 2018
By Chad McNutt
There’s a memorable passage at the beginning of Elmer Kelton’s book, The Time it Never Rained, about the 1950s drought in Texas: “Why worry they said. It would rain this fall. It always had. But it didn’t. And many a boy would become a man before the land was green again.”
It’s hard to read those lines and not think about the optimism behind them. “It’ll rain eventually, and I can feed my cattle until things get better.” Drought is often described as insidious, meaning that it has a tendency to sneak up on you. It can also last for years and sometimes it’s hard to know when a drought is even over.
Kelly Redmond, a climatologist from the University of Nevada, Reno, once said it was possible to have a short-term drought occur while in the middle of a slightly longer-term wet period inside of a much longer drying trend. Considering that, it can make you think about drought on a longer timescale.
The frequent droughts that occurred in Texas and Oklahoma in 2006, from 2011 to 2015, and now in 2018, certainly had wet years in between. The question, however, is how much of a memory can those drought events, especially given how intense the 2011 drought was, have in systems like our range and croplands.
In other words, even though we say a drought is over, are there lingering or less obvious impacts that can sneak up on you over time?
To add a bit more perspective to this question, look at the map of Texas and Oklahoma that shows the number of weeks each county has been in Exceptional Drought (D4) since the beginning of 2005. Exceptional Drought is the highest drought category used in the U.S. Drought Monitor. Statistically, it should occur about 2% of the time or about once every 50 years. The data are several weeks old, but several counties in Texas and Oklahoma have been in Exceptional Drought for over 200 weeks, or about 30% of the time since 2005. That is way outside what would be expected and is certainly exceptional.
Gary McManus, Oklahoma state climatologist, is one of the experts tracking drought for the state. He communicates with a large network of farmers and ranchers, along with groups like county Extension agents and USDA’s Farm Service Agency. McManus takes input from these groups and provides it weekly to the U.S. Drought Monitor.
Over the last few years, he has noticed the usual climate and meteorological indictors used to track drought do not always correspond well with the impacts that producers are seeing on the ground. The impacts are often more severe, or faster to develop, than what he would expect just going by the data. I contacted McManus because we have been hearing about this issue and I was curious to know what was causing the disconnect between the monitoring data and what producers are seeing in their fields and pastures.
There is ongoing debate within the scientific community about the lingering or cumulative influence of droughts over time. Monitoring and tracking drought is something we are really good at, but unfortunately, we are less adept at understanding all the ecological interactions and feedbacks that occur and thus drive drought-related impacts.
According to Redmond, “Like the tree falling in the forest, does drought occur if there is no human to record or experience it?” He was getting at the importance of seeing drought through its impacts and not just the indicators we have designed to track it. Just because our data do not show an intense drought, it doesn’t necessarily mean there aren’t impacts being experienced.
The question I specifically was interested in was whether the string of droughts over the last 12 or 13 years could have affected something fundamental, like the structure and function of the soils in parts of Oklahoma, and therefore key soil qualities like water holding capacity. McManus couldn’t say if it was something as fundamental as changes in the soil but he noted that “ag producers are saying the droughts are more intense than what the indicators are saying.”
He further explained that he is hearing that they have been going into drought much sooner than what he would expect and that when they do get some moisture, it is not lasting as long. In Harper County, Okla., where Gary is originally from, he has noticed the water table has not fully recovered since the 2011 drought. He noted that spring-fed ponds used to be reliable, and now, even after good rains, the ponds are going dry relatively quickly.
On Gary’s recommendation, I contacted Tyson Ochsner, associate professor and soil scientist from Oklahoma State University. I asked Ochsner what he thought about the droughts in Oklahoma and Texas and whether they could still be having an impact, and in particular, a lasting impact on the soils in Oklahoma.
“I don’t really have the data but can imagine how it might happen,” he said. Ochsner explained that 2011 was a brutal year and that a lot of pasture and cropland were hit hard. Without vegetative cover and with little residue being returned to the soils, it is likely these harsh droughts have caused a loss of topsoil, increased soil compaction, and as a consequence, reduced water infiltration and reduced the water availability capacity of the soils.
One stark example was the dust storm that shut down I-35 in October 2012. Ochsner explained that the dust wasn’t just coming from cropland, but the range was also contributing to the massive amount of dust being generated due to a lack of vegetative cover. “If we lose topsoil to wind and or water erosion, we are going to reduce water availability capacity,” he explained.
A rule of thumb in Oklahoma has always been that you’re never more than two weeks away from a drought, Ochsner said. Oklahoma soils do not have a large water storage capacity to start with. “Best case scenario, take the top 32 inches of soil and that might store 8-9 inches of water. [Then, you] Get into peak of summer with evapotranspiration rates approaching half inch a day. That doesn’t give you many days of actual supply.”
We discussed that it’s possible the erosion of topsoil from the successive droughts since 2005 may have reduced that two-week rule of thumb to something like maybe 10 or 13 days. That could be a big deal and one of the reasons we are seeing a disparity between our indicators and impacts on the ground. Bottom line, there’s a chance we don’t have the same amount of reservoir capacity in the soils we did prior to all these drought events.
This is not good news as we are in the middle of another drought in parts of the Southern Plains. The most recent three-month forecast is showing it could be another hot and dry summer, and in many places, we are going into it with severe moisture deficits.
There is some good news, though. Ochsner and I left our conversation with him telling me that he and colleagues at OSU have soil samples from several sites across the state that were sampled before the 2005 drought. They will compare them to samples taken more recently to look at this question of changes in soil structure and composition. So, while this question about how we observe drought and understand the potential cumulative impacts is still out there, at least we recognize there is a problem and isn’t that the first step in getting help.
This story was adapted from an article in the Livestock Weather Journal, which is a publication of Livestock Wx. Chad McNutt is the co-founder of Livestock Wx and editor of the Livestock Weather Journal.
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