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- Title
The Decline in Summer Fallow in the Northern Great Plains Cooled Near‐Surface Climate but had Minimal Impacts on Precipitation.
- Authors
Stoy, P. C.; Bromley, G. T.; Prein, A. F.; Albeke, S. E.
- Abstract
Land management can moderate or intensify the impacts of a warming atmosphere. Since the early 1980s, nearly 116,000 km2 of cropland that was once held in fallow during the summer is now planted in the northern North American Great Plains. To simulate the impacts of this substantial land cover change on regional climate processes, convection‐permitting model experiments using the Weather Research and Forecasting model were performed to simulate modern and historical amounts of summer fallow. The control simulation was extensively validated using multiple observational data products as well as eddy covariance tower observations. Results of these simulations show that the transition from summer fallow to modern land cover led to ∼1.5°C cooler temperatures and decreased vapor pressure deficit by ∼0.15 kPa during the growing season across the study region, which is consistent with observed cooling trends. The cooler and wetter land surface with vegetation led to a shallower planetary boundary layer and lower lifted condensation level, creating conditions more conducive to convective cloud formation and precipitation. Our model simulations however show little widespread evidence of land surface changes effects on precipitation. The observed precipitation increase in this region is more likely related to increased moisture transport by way of the Great Plains Low Level Jet as revealed by the ERA5 reanalysis. Our results demonstrate that land cover change is consistent with observed regional cooling in the northern North American Great Plains but changes in precipitation cannot be explained by land management alone. Plain Language Summary: The northern part of the North American Great Plains have seen a globally‐unique early season climate cooling over the past five decades, with a corresponding increase in precipitation. This cooling and moistening trend has coincided with a large‐scale decrease in the practice of leaving fields bare ("fallow") during the growing season that was recommended in the early twentieth century to help conserve water for subsequent crops. Fallow fields can become quite hot in the absence of cooling from plant transpiration, and add less moisture to the atmosphere that can help contribute to rainfall. Cooler and moister air that arises from planted fields can make precipitation more likely, but is this the cause of observed climate trends in the northern Plains? We ran the Weather Research and Forecasting Model with historical and modern expanses of fallow on the land surface. Model results are consistent with observed early growing season climate cooling but do not predict substantial changes in precipitation, which instead are more consistent with additional moisture transport from the southern border of our study region. Key Points: Early growing season cooling in the northern North American Great Plains is consistent with summer fallow reductionWeather Research and Forecasting model predictions indicate that fallow reduction does not explain increases in precipitationIncreased moisture transport from the Great Plains Low Level Jet is consistent with observed increases in precipitation
- Subjects
GREAT Plains; ATMOSPHERIC boundary layer; METEOROLOGICAL research; WEATHER forecasting; SHIFTING cultivation; FALLOWING; PLANT transpiration; VAPOR pressure
- Publication
Journal of Geophysical Research. Atmospheres, 2024, Vol 129, Issue 12, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD040699