Adaptation of an aridity index for mid-season evaluation of Midwest corn yield
A modified aridity index was presented as a risk management tool for assessing possible Midwest corn yields during the growing season. The modifications were the reduction from a monthly scale to a weekly scale and the inclusion of a weighting scheme to account for corn development. Most crop yield models utilize the relationship of yield (percentage of potential) to evapotranspiration (percentage of potential). Sub-monthly indexes involving fairly direct evaluations of evapotranspiration for crop assessment have been developed in the past with satisfactory results. However, the evaluation of actual and potential evapotranspiration for these index computations is not easy to assess in near real-time because some data for input are not readily available (e.g., pan evaporation, net radiation, soil water). The aridity index, which accounts for evapotranspiration indirectly with readily available daily maximum temperature and daily precipitation data, is presented as a near real-time alternative. A model was established on the relationship between the aridity index and corn yield on data from 1980 to 1999. The relationship was tested on the 2000 and 2001 growing seasons and was found useful for evaluating the chance of yield being above or below trend. Because of the usefulness of the aridity index, a way to display it for the Midwest in near real-time was produced.