CHICAGO, April 30 (Xinhua) -- Data from the past three decades suggest that excessive rainfall can affect crop yield as much as excessive heat and drought, according to a study released by the University of Illinois (UI) on Tuesday.

In the study, UI researchers linked crop insurance, climate, soil and corn yield data from 1981 through 2016. They found that during some years, excessive rainfall reduced U.S. corn yield by as much as 34 percent relative to the expected yield, while drought and excessive heat caused a yield loss of up to 37 percent during some years.

"We linked county-level U.S. Department of Agriculture insurance data for corn loss with historical weather data, letting us quantify the impact of excessive rainfall on yield loss at a continental scale," said Kaiyu Guan, a natural resources and environmental sciences professor and the study's principal investigator. "This was done using crop insurance indemnity data paired with rigorous statistical analysis - not modeled simulations - which let the numbers speak for themselves."

The researchers also found that the impact of excessive rainfall varies regionally.

"Heavy rainfall can decrease corn yield more in cooler areas and the effect is exacerbated even further in areas that have poor drainage," said Yan Li, a former UI postdoctoral researcher and lead author of the study.

Excessive rainfall can affect crop productivity in various ways, including direct physical damage, delayed planting and harvesting, restricted root growth, oxygen deficiency and nutrient loss, the researchers said.

The findings have been published in the journal Global Change Biology.