The calendar has flipped to 2013 and the drought of 2012 is continuing in Iowa and a large section of the United States. The eastern Corn Belt has seen some relief, but the western Corn Belt and the Great Plains continue to be quite dry. Wallaces Farmer this week listened to presentations by Iowa weather experts Harry Hillaker and Elwynn Taylor, who gave an update and outlook on the situation as it appears for the new year.
Although rainfall earlier in December increased topsoil moisture in much of Iowa, not much has changed regarding total soil moisture supplies over the past few months. Subsoil in most of Iowa remains dry. The year 2012 went into the record books as one of the warmest years on record at many locations in and around Iowa, and at a number of locations it was one of the driest years ever.
December brought little chance of replenishing reserve soil moisture supplies before spring. Figures compiled by Hillaker, the state climatologist with the Iowa Department of Agriculture, show Iowa ended 2012 with 26.31 inches of total precipitation, which is 8.96 inches below normal. The annual average for Iowa is 35.27 inches, he says.
Despite snowfall, drought conditions will likely continue into spring
Yes, there was a big snowstorm in a large section of Iowa right before Christmas. But it's hard to break a drought with snow. It would take a lot of snow. A foot of snow provides about an inch of water, more or less. The long-term average is 13.3 inches of snow equates to an inch of water in Iowa but that varies from one storm to the next. A foot of snow equaling an inch of water is a "close enough" thumb rule to use, says Hillaker. As of the second week of January 2013, Iowa is running about a 9 inch rainfall deficit. It would take 9 or 10 feet of snow to break the drought—an unlikely event.
Of course, snow melt runs off instead of soaking into frozen ground which is another consideration. The wide swings in temperature we've seen in January from one side of normal to the other will likely be a feature of Iowa weather during the remainder of this winter, he says, with the pattern not likely remaining the same for long periods of time.
Historically, years with a rainfall deficit of the magnitude of 2012 don't recover to normal annual precipitation in a single year, says Taylor, the Iowa State University Extension climatologist. An additional year of significant dry weather is considered likely in 2013 and a fourth consecutive year of below trend U.S. corn yield is a distinct possibility. That's the message Taylor is delivering to farmer meetings around the state and the Midwest this winter.
It is unlikely that subsoil moisture supply will be fully recharged in many Iowa fields by start of 2013 planting
Crop roots reached deeper than usual in 2012 to produce a greater-than-anticipated yield in many locations in Iowa, but that resulted in 8 to 9 feet of moisture depleted soil and a requirement of about 16 inches or more of rain needed to replenish subsoil moisture for the 2013 crop. A foot of soil profile holds about 2 inches of water at full capacity. Considering the amount needed to make up the moisture deficit and how dry much of Iowa is this winter, Taylor says it is unlikely subsoil moisture will be fully recharged statewide by the start of the planting season.
Eastern Iowa caught some rain this past fall and is in better shape than western Iowa. Hillaker says the eastern third of the state could see its subsoil moisture supply climb back up to normal if Iowa receives good rains this spring. Going into winter, about 72% of the state was running "short to very short" on subsoil moisture.
The driest area of Iowa this winter is far northwest Iowa, which had an extremely dry fall in 2012. "There, in the driest areas, they probably now have less than a third of their normal amount of subsoil moisture," says Hillaker. "That's not good. Normal spring rainfall wouldn't bring them up to field capacity. It would take a wetter-than-normal spring to get those extremely dry areas turned around." He says the area of Iowa with the greatest deficiency in subsoil moisture is roughly north of a line from Sioux City to Spencer and then to approximately Forest City.
La Nina vs. El Nino situation remains in neutral, which creates a lot of uncertainty in regard to weather for 2013 growing season
Climatologists were hoping this past fall that the weather pattern would change to an El Nino situation, which would be favorable for the U.S. Corn Belt. But that hasn't happened. "We are still in neutral in regard to La Nina versus El Nino," says Hillaker, "and that is basically the expectation through winter and spring, and maybe next summer. Usually, it is late summer before La Nina and El Nino events and weather patterns switch to a great degree."
Temperature measurements of the ocean's surface water in the Tropical Pacific along the equator are what determine whether an El Nino or a La Nina event is occurring. "As we are now moving into mid-January 2013, the situation remains in neutral and it appears these neutral conditions will continue for the first few months of this year, with no indication of either El Nino or La Nina forming," adds Taylor.
It would take 18 inches of rain this spring to completely recharge subsoil moisture in fields where corn roots reached 9 feet deep last summer
Talking to farmers, Taylor is speaking at a lot of meetings all over Iowa and in neighboring states this winter. "The big concern is that the subsoil moisture supply was tapped out in 2012 in many fields," he says. "It wasn't replenished last fall, so will we get the necessary rains to recharge the subsoil moisture this spring?"
Taylor says subsoil moisture reserves in the drier areas of Iowa are so well tapped out that it is "now very dry, beyond anything we've seen in the last 20 years. Each foot of soil profile can hold about 2 inches of water available to plants. And that reserve moisture in many areas of Iowa and in some other states is now gone, not just in the top 5 feet of soil like we usually expect, but all the way down to 9 feet in many fields. It would take 18 inches of rain this spring to get the subsoil moisture supply completely recharged. That is unlikely to occur."
To keep tabs on the drought situation each week, visit the U.S. Drought Monitor website at droughtmonitor.unl.edu.