Value of Summer Season Precipitation Predictions in Decisions about Use of Precipitation Modification

Abstract

Results from a prior investigation of crop-yield shifts produced by simulated summer rain increases were coupled with summer rainfall forecasts to assess the possible economic outcomes of using forecasts to select the level of rain change for a summer. Simulated rain increases tested ranged from 10% to 40%. values not scientifically established as possible from midwestern cloud seeding, but chosen to provide a wide range of conceivable changes. The yields of corn and soybeans, under these different levels of simulated rain increases and grown under various growing season conditions experienced during a five-year agricultural plot experiment, varied considerably. To test the value of using a forecast, a summer rain forecast (above, below, or new average) made on 1 June and with an accuracy of 60%, was used as a guide to select the amount of rain change to use in each of the five test years. Then, the distribution of the financial gain from crop yields obtained was computed. The use of the forecasts showed an expected gain in 85% of the annual cases studied. Use of this forecasting skill (and hence less than perfect choice of level of precipitation augmentation to use in a given year), produced a gain in revenue expected over the five-years test period of 1.6% of the crop value, a possible maximum gain of 3.8%, and a possible maximum low of 0.6%. Rain increase applied without use of summer rain predictions (and based on use of the added rain level found best for continuous use in all five years) provided a revenue gain of only 0.4%, considerably less than the value obtained with the forecasts. If perfect rain forecasts existed, the expected gain would be 4.5% of the crop value. Even with a rain-modification technology that could deliver 10%, 25%, or even 40% rain increases in any given summer, the agricultural value of rain augmentation in Illinois done over a series of years is relatively small, even when coupled with forecasts.