Winter wheat, which accounts for about three-fourths of U.S. wheat production, is sown in the fall and harvested in the late spring or early summer. During early spring, the mature wheat crop forms a swath about 150 km wide that extends from southwest Oklahoma into north central Oklahoma and southern Kansas. On either side of this band is sparse or dormant vegetation, especially in extreme western Oklahoma and the Panhandle. In the late spring or early summer, wheat is harvested and previously dormant grassland has grown, resulting in a band of short stubble and bare soil surrounded by mature prairie grasses. Given these conditions and the extensive set of near-surface measurements from its Mesonet, Oklahoma is an optimal real-world environment to examine mesoscale vegetative influences on the atmosphere.

The presenter will document that, during growth and after harvest, Oklahoma’s winter wheat belt has a significant impact on the near-surface, mesoscale environment. Differences in near-surface atmospheric variables across the wheat belt and its adjacent lands are documented using the following methods: (1) observational analyses of monthly averaged daily statistics (e.g., daily maximum or minimum) during Crop Year 2000, (2) observational analyses of daily averages and instantaneous measurements for several case study days during Crop Year 2000, (3) statistical analyses of daily statistics from 1994 through 2001, and (4) numerical simulations of case study days during Crop Year 2000 that applied two different land uses over the wheat belt region for comparison.

Analysis results from these different methods are consistent and establish a convincing case that the crop belt modifies both the mesoscale climatology and, on many days, the daily weather of Oklahoma. Consequently, it is imperative that mesoscale forecasts, whether produced objectively or subjectively, account for the vegetation-land-air interactions that occur across western Oklahoma and, presumably, across other crop regions in the U.S. and around the globe.