Surface resistance controls differences in evapotranspiration between croplands and prairies in U.S. Corn Belt sites

Authors: Schreiner-Mcgraw, Adam; Baker, John; WOOD, JEFFRY - University Of Missouri; ABRAHA, MICHAEL - Michigan State University; CHEN, JIQUAN - Michigan State University; GRIFFIS, TIMOTHY - University Of Minnesota; ROBERTSON, G - Michigan State University

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2024
Publication Date: 4/1/2024
Citation: Schreiner-McGraw, A.P., Baker, J.M., Wood, J.D., Abraha, M., Chen, J., Griffis, T.J., Robertson, G.P. 2024. Surface resistance controls differences in evapotranspiration between croplands and prairies in U.S. Corn Belt sites. Water Resources Research. 60(4). Article e2023WR035819. https://doi.org/10.1029/2023WR035819.
DOI: https://doi.org/10.1029/2023WR035819

Interpretive Summary: Water returned to the atmosphere as evapotranspiration (ET) includes evaporation from soil and plant leaves. Global ET is approximately 1.6x greater than global river flow and has wide-reaching impacts on groundwater and streamflow. In the U.S. Midwest, widespread land conversion from prairie to cropland has altered patterns of ET, yet there is no consensus on the direction of change in ET or the mechanisms controlling changes. In this study we use measurements of ET at three locations within the Long-Term Agroecosystem Research (LTAR) network that have paired cropland and prairie sites. Surprisingly, we found that in the two northern sites, the croplands had higher ET than the prairies, particularly during springtime when the croplands are fallow. We used mathematical analysis of the energy budget to show that a parameter called the surface conductance controls the differences in ET between the croplands and prairies. The surface conductance represents how easily both heat and water vapor can be transferred from the land surface to the atmosphere. During springtime in the prairies, the standing, dormant vegetation blocks transfer of water vapor from the land surface and limits the ET. Results from this study provide critical insight into the impact of land conversion from prairies to croplands on the hydrology of the U.S. Corn Belt by providing a mechanistic understanding of how land use change affects the water budget.

Technical Abstract: Water returned to the atmosphere as evapotranspiration (ET) is approximately 1.6x greater than global river discharge and has wide-reaching impacts on groundwater and streamflow. In the U.S. Midwest, widespread land conversion from prairie to cropland has altered spatiotemporal patterns of ET, yet there is no consensus on the direction of change in ET or the mechanisms controlling changes. We aimed to harmonize findings about how land use change affects ET in the Midwest. We measured ET at three locations within the Long-Term Agroecosystem Research (LTAR) network along a latitudinal gradient with paired rainfed cropland and prairie sites at each location. At the northern locations, the Upper Mississippi River Basin (UMRB) and Kellogg Biological Station (KBS), the cropland has annual ET that is 84 and 29 mm/year higher, respectively, caused primarily by higher ET, likely from soil evaporation during springtime when agricultural fields are fallow. At the southern location, the Central Mississippi River Basin (CMRB), the prairie has 69 mm/year higher ET, primarily due to a longer growing season. To attribute differences in springtime ET to specific mechanisms, we examine the energy balance using the Two-Resistance Method (TRM). Results from the TRM demonstrate that higher surface conductance in croplands is the primary factor leading to higher springtime ET from croplands, relative to prairies. Results from this study provide critical insight into the impact of land use change on the hydrology of the U.S. Corn Belt by providing a mechanistic understanding of how land use change affects the water budget.