Ag Weather Forum

While derechos may not be on producers' minds as we head into winter, a recent study takes a new approach to determine how crop yields and ratings are affected by derechos in the United States.

Derechos are long-lived windstorms that are associated with rapidly moving rain showers and thunderstorms. These storms can provide widespread damage and have detrimental impacts on crop yields.

In a recent study published in October, Northern Illinois University researchers and an employee from the reinsurance company, Guy Carpenter, took a new approach to studying how derechos affect crop ratings and yields. The study leveraged USDA crop condition data during a nine-year period, from 2015 to 2023, and overlapped the crop conditions with derecho footprints.

Previous studies have looked at the effects of strong winds and heavy precipitation on crops, but this study emphasized a knowledge gap on the understanding of the broader impacts of derechos on crop conditions and yields. Other studies have also relied more heavily on satellite data to determine crop damage from derechos, but satellite data has some limitations from cloud cover.

The authors of this recent study used the USDA's National Agricultural Statistics Service (NASS) crop condition dataset, and it allowed them to study county-level impacts of derechos on corn and soybeans. By using the NASS dataset, they were able to calculate the Crop Condition Index, or CC Index, to help with their assessment of crop conditions in derecho-affected areas. With a range from 1 to 5, a CC Index of 5 corresponds to 100% of a surveyed crop reported in excellent condition while a CC Index of 1 corresponds to 100% of a surveyed crop reported in very poor condition.

Out of 79 derechos that were examined in the central and eastern U.S. from 2015 to 2023, researchers found that the highest frequency of derechos occurred within the Corn Belt and eastern portion of the Great Plains. The top five corn and soybean producing states reside in these areas and contribute 60% and 53% of the national corn and soybean production, respectively. Approximately 90% of the national corn and soybean acreage experienced at least one derecho throughout the nine years included in the study.

Researchers discovered that the derecho that hit Iowa and Illinois on Aug. 10, 2020, was the most detrimental to corn and soybean production within the 2015-23 period. Story County, Iowa, had a maximum CC Index of 1.23 proceeding that derecho. However, over the nine years studied, Illinois experienced the most negative derecho impacts on corn and soybeans. The county-mean maximum CC Index decline was 0.33.

Additionally, those counties affected by a derecho saw an overwhelming decline in crop conditions whereas only a small number of counties saw a net benefit following a derecho. States such as Michigan, Pennsylvania and Louisiana were amongst the states that saw net benefits after a derecho. However, this brings up an important relationship between crop exposure and derecho risk. These are states outside of the Corn Belt that do not have as high cropland density and their derecho risk is lower compared to states within the Corn Belt.

This study also looked at derecho impacts on crop conditions within different times of the growing season. During the early growing season, derechos that hit in May would lead to improvements in crop conditions and yields for both corn and soybeans. This is due to rapid vegetative growth and plants can often recover if damage is not severe.

The months of June and July showed more pronounced declines in crop conditions and yield. Corn and soybeans are entering critical growth stages as corn starts to silk and soybeans start to flower. In June, the mean yield change ranged from zero to 1% for corn and soybean-producing counties within a derecho footprint. By August, 61% of corn-producing counties declined in conditions and yield after a derecho moved through. On the other hand, 56% of soybean-producing counties showed a decline in conditions and yield.

Researchers also hypothesized that preexisting growing conditions can influence how crops respond and recover from a derecho. Soil moisture was one of the key factors. If a derecho brought heavy rain to an area in May, both corn and soybeans would see a mean improvement in the CC Index ratings. Yields could increase from 1.1-6.3%. Later in the growing season, prolonged drought stress followed by a sudden increase in precipitation didn't lead to significant improvements in crop conditions and yield. Drought-stressed plants can often have reduced root function and diminished leaf area, forcing a slower recovery rate.

Overall, a crop's response to derechos depends on more than just the strength of the derecho. Location, crop growth stage, preexisting conditions, and post-event weather patterns can all influence the response of the crop. Yet, if a derecho caused conditions and yield prospects to decline immediately after the storm, conditions would continue to decline through the rest of the growing season.

To read the full study, visit: https://www.sciencedirect.com/….

Teresa Wells can be reached at teresa.wells@dtn.com

(c) Copyright 2025 DTN, LLC. All rights reserved.