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Recent research highlights the significant impact of land use changes and irrigation practices in the U.S. Corn Belt on local precipitation patterns, fundamentally altering the climate of this key agricultural area.
The study, which appears in the Proceedings of the National Academy of Sciences, investigates the phenomenon of “precipitation recycling.” This process involves the atmospheric moisture released by various natural features—such as plants, soils, and water bodies—returning to the same region as precipitation.
Utilizing sophisticated computer modeling techniques, researchers discovered that agricultural activities in conjunction with shallow groundwater significantly enhance the precipitation recycling ratio by nearly 30%. This increase plays a crucial role in bolstering rainfall during the growing season, which is essential for crop development.
The researchers noted that the degree of precipitation recycling fluctuates throughout the year and across different years. It tends to peak during the summer months, aligning with the growth cycle of corn crops, and in years experiencing low moisture influx from external sources.
Lead author Zhe Zhang from the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR) emphasized the implications of this research for food and water security: “Understanding how agricultural practices can influence regional climate is critical, especially in the U.S. Corn Belt, where consistent rainfall is fundamental for both farmers and water resource managers.” He underscored the importance of recognizing the origins of rainfall.
Insights derived from this study could enhance future rainfall forecasts for the Corn Belt, providing valuable information that could assist in developing planting strategies and managing water resources more effectively.
This research involved collaboration among various scientists from NSF NCAR, the Hong Kong University of Science and Technology, and the University of Santiago de Compostela in Spain, and was supported through funding from NSF.
Transformations in Land Use
The U.S. Corn Belt encompasses multiple states across the Midwest and Great Plains, stretching from Ohio in the east to Nebraska in the west. Historical accounts indicate that before European colonization, this area consisted of diverse tallgrass prairie and woodlands. Currently, however, it is predominantly agricultural land with extensive irrigation systems.
Prior studies have documented an increase in humidity and rainfall in the region. Nonetheless, Zhang and his team aimed to quantify the specific impact of precipitation recycling.
To achieve this, researchers employed the NSF NCAR Weather Research and Forecasting (WRF) model, known for its high-resolution atmospheric simulations at four kilometers. They also utilized the Noah-MP model, which allows for comprehensive examination of groundwater interactions, crop growth, and irrigation effects. By applying a physically accurate algorithm, they traced water vapor movement within their simulations.
To isolate the influences of agriculture and the region’s natural shallow groundwater, simulations that included various combinations of crops, irrigation, and groundwater were compared against models lacking some of these elements. These simulations were run at the NSF NCAR-Wyoming Supercomputing Center.
The results indicated that the precipitation recycling ratio—measuring the proportion of local precipitation attributable to these processes—was 18% due to the interplay of shallow groundwater, corn plants, and irrigation evaporation. In contrast, models without these factors showed a reduced precipitation recycling ratio of only 14%, representing a 29% decrease.
Focusing their analysis on three distinct years—2010 (a notably wet year), 2011 (average conditions), and 2012 (a dry year)—the researchers found that recycled precipitation was most prominent in 2012, a year with minimal moisture contributions from sources like the Gulf of Mexico.
“Our ability to clarify the contributions of different processes to precipitation changes has important implications,” stated Zhang. “Since agriculture is heavily dependent on rainfall, these insights can guide effective management of agricultural practices and water availability.” He and his research team are planning further investigations to examine how shifting precipitation trends might influence agricultural productivity.
This research was conducted with support from the NSF National Center for Atmospheric Research, a facility backed by the U.S. National Science Foundation and managed by the University Corporation for Atmospheric Research. The views, findings, and recommendations expressed in this material do not necessarily represent those of NSF.
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