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. the first estimate of the effects of seeding on precipitation timing, duration, intensity and amount. o Multidimensional cloud models. - This class of model attempts to simulate the full three-dimensional structure of a developing cloud. In some cases, the model can be extended to permit examination of interactions between adjacent clouds or between clouds ancl the larger environment. Models which nest one cloud model within anclther allow for large spatial coverage at low resolution /to establish the proper large-scale flow within which clouds are embedded, while alt the same time permitting high resolution in limited spatial regions, where the clouds form. Such models, however, cannot usually describe the details of the microphysics within the clouds, and are based on parameterization of the microphysical processes. Models of this sort require large mainframe computer or "supercornputers," but can give the most realistic picture of the dynamical complexities a,nd influen- ces on cloud and precipitation evolution. A limited number of experiments should be made with this model to examine the relationship between individual cloud structure and the larger-scale meteorological and topographic forcing. Such results should be used to make estimates of the effects of larger-scale dyna- mic forcing on precipitation development and its spatial distribu- tion. It should provide realistic flow fields necessary t.o initiate the multilevel models where most of the deta'iled seeding investiga- tions should be performed. In addition, this model should be used to investigate possible large-scale responses to seeding. 4. DeSign of demonstration project The assessment team believes that a scientifically-based demonstration project (i.e., a substantial and sound scientific experiment) is urgently needed to quantitatively assess the full effects of cloud seeding in Thailand. This view appears to be supported by all Thailand government, university and private groups that the team contacted. For the reasons given in Part IV, section A.3, the catchment area of the Bhumipol Reservoir is the recommended location for the demonstration project. The dimensions of a proper scientific demonstration project include the specification of objectives and scope, physical conceptual models, sta- tistical treatment effect models, variables and measurements, treatment design or plan, treatment allocation, data collection procedures, data- base construction and data analyses. A few of these items are briefly described here; t~e weather modification literature (e.g., Brier, 1974; Tukey et al., 1978; Flueck, 1978, 1986; Bureau of Reclamation, 1979, 1982) should be consulted for a more comprehensive and detailed discussion of the design of experiments. ., . .., . 51