Projected long-term climate trends reveal the critical role of vapor pressure deficit for soybean production in the US Midwest

Authors: SUN, WENGUANG - University Of Nebraska; Fleisher, David; Timlin, Dennis; RAY, CHITTARANJAN - University Of Nebraska; WANG, ZHUANGJI - University Of Maryland; BEEGUM, SAHILA - University Of Nebraska; Reddy, Vangimalla

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2023
Publication Date: 3/21/2023
Citation: Sun, W., Fleisher, D.H., Timlin, D.J., Ray, C., Wang, Z., Beegum, S., Reddy, V. 2023. Projected long-term climate trends reveal the critical role of vapor pressure deficit for soybean production in the US Midwest. Science of the Total Environment. 878. Article e162960. https://doi.org/10.1016/j.scitotenv.2023.162960.
DOI: https://doi.org/10.1016/j.scitotenv.2023.162960

Interpretive Summary: The Mid-West in the United States (U.S.) is a major soybean-producing region with a high level of economic importance and accounts for 34% of world soybean production. Climate extremes such as heat waves and droughts during recent years have once again raised concerns about the capacity of the region to remain as a large soybean production. Here, we use a well-validated GLYCIM soybean model and an ensemble of downscaled climate forcing from the CMIP5 models to map soybean yield production for three different current and future decades under different climate scenarios. Our work showed that the number of hot days that negatively influence soybean yield are expected to increase. These hot days were linked with dryer air which can be associated with vapor pressure deficit (VDP). Higher VPD was shown to increase drought and crop losses under future climate conditions. Results also showed that except the northernmost Midwest counties, most of the current soybean planting area will experience yield losses if atmospheric carbon dioxide levels (CO2) remain at today's levels. Higher CO2 levels, as expected for the near future, can offset a significant portion of this yield loss. These findings highlight the importance for scientists to consider the impact of higher VPD along with high temperature and low rainfall trends when assessing climate impacts. These results can be used to help identify adaptation approaches and mitigation strategies and identify opportunities for breeding programs and crop management.

Technical Abstract: Extreme weather events such as heat waves and droughts are projected to become more frequent under future climate change conditions, yet the mechanisms between soybean yields and climate factors, specifically trends involving variable rainfall and high heat episodes across a large spatial scale are still unclear. The current work utilized the mechanistic soybean model, GLYCIM, newly modified with an improved surface runoff model based on Saint-Venant equation, to evaluate rainfed soybean production across 13 US Midwestern states at a 10 km spatial resolution for three periods (2011 -2020, 2051 -2060, 2091 -2099) under Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios, respectively. Results showed that except the northernmost Midwest counties, most of the current soybean planting area suffers from yield losses without considering the [CO2] effect under different climate projected scenarios. The positive effect of CO2 fertilization on yield is apparent under both RCP scenarios and is consistent across all regions and all climate projections. Our statistical analysis indicated that the increased frequency of extreme degree days (EDD) or accumulation of hourly temperatures above 30 oC associated with increased vapor pressure deficit (VPD) play the key role in contributing to water deficits and crop losses under future climate conditions. Although the results suggest a relatively weak relationship between summer rainfall and crop yields in this region, decreasing rainfall causes increased VPD and thus induces crop water deficits. These findings imply the importance of considering VPD along with high temperature and low rainfall trends simultaneously for future agronomic adaptation and mitigation strategies, particularly for breeding programs and crop management.