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<br />. The expected effects of.a successful weather modification <br />program on seasonal snow accumulation and melt can be determined by <br />a relatively simple simulation experiment. There are several sites in <br />the Sierra Nevada where measurements have been made of each snowfall <br />over a period of years. Several simulated weather modification policies <br />should be applied to these data, assuming appropriate, and stochastically. <br />varying, percentage increases in snowfall for each storm chosen for <br />seeding. The simulated season-long accumulation and disa ppearance <br />patterns can be compared with the recorded amounts to estimate the <br />expected range of variation in responses to a weather modification <br />program. <br /> <br />. A simulation study should be carried out to determine <br />the probable effect of the postulated snow augmentation on the accumulation <br />of snow in space and in time, and on snowmelt rates and amounts. <br />Existing models are adequate for such a simulation study without a <br />great deal of additional effort. Weather records and snow course records <br />are available for a number of representative sites in the Sierra Nevada. <br />Several alternate assumptions about decision policies for snow <br />augmentation can be applied to these records, with stochastic variation <br />built into the simulation to account for uncertainty associated with the <br />cloud seeding operation itself. The actual snow accumulation at various <br />dates can then be compared with the simulated results; repeated runs of <br />the simulation will permit estimating the variance of the difference. <br />Snowmelt and moisture depletion equations are available to test the <br />simulated effect of snow augmentation on these variables. The Pacific <br />Southwest Forest and Range Experiment Station of the U. S. Forest <br />Service, the California Cooperative Snow Survey of the California <br />Department of Water Resources, the U. S. Geological Survey at Menlo <br />Park, and several university groups are in a position to provide data <br />and expertise for such a program. <br /> <br />11 <br />