VALUE OF SUMMER SEASON PRECIPITATION PREDICTIONS IN DECISIONS ABOUT USE OF PRECIPITATION MODIFICATION

Results from a prior investigation of crop-yield shifts produced by si mulated summer rain increases were coupled with summer rainfall foreca sts to assess the possible economic outcomes of using forecasts to sel ect the level of rain change for a summer. Simulated rain increases te sted ranged from 10% to 40%, values not scientifically established as possible from midwestern cloud seeding, but chosen to provide a wide r ange of conceivable changes. The yields of com and soybeans. under the se different levels of simulated rain increases and grown under variou s growing season conditions experienced during a five-year agricultura l plot experiment, varied considerably. To test the value of using a f orecast, a summer rain forecast (above, below, or near average) made o n 1 June and with an accuracy of 60%, was used as a guide to select th e amount of rain change to use in each of the five test years. Then, t he distribution of the financial pin from crop yields obtained was com puted. The use of the forecasts showed an expected pin in 85% of the a nnual cases studied. Use of this forecasting skill (and hence less tha n perfect choice of level of precipitation augmentation to use in a gi ven year), produced a gain in revenue expected over the five-year test period of 1.6% of the crop value, a possible maximum gain of 3.8%, an d a possible maximum loss of 0.6%. Rain increase applied without use o f summer rain predictions (and based on use of the added rain level fo und best for continuous use in all five years) provided a revenue pin of only 0.4%, considerably less than the value obtained with the forec asts. If perfect min forecasts existed, the expected pin would be 4.5% of the crop value. Even with a rain-modification technology that coul d deliver 10%, 25%, or even 40% min increases in any given summer, the agricultural value of rain augmentation in Illinois done over a serie s of years is relatively small, even when coupled with forecasts.