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SUMMARY REPORTS OF WORKING GROUPS Abiotic Processes (Dr. Charles F. Leaf, Convener) The abiotics group developed the analytical framework shown in figure 1 to show the interactions that relate events at the atmospheric level (precipitation) to those occurring at the terrestrial level (microclimate, erosion, avalanches, and water yield) and on down to the aquatic level (fluvial geomorphology and water quality). The line weight of the interconnecting arrows shows not how strong the linkages are but how well understood they are. A sensitivity matrix was prepared showing, for each of these abiotic events, the settings wherein they are most important, the processes through which they operate, and the magnitude of the expected response to prolonged precipitation augmentation. Figure 2, an abridgement from the group's report, shows the portion of the matrix for which detectable responses were expected, given a prolonged precipitation augmentation of 20 percent, together with an estimate of the state-of-the-art with respect to measurement of the responses. This matrix suggests that, when all forms of response are considered, alpine areas will show the most readily detectable responses to precipitation management. This assessment of alpine response requires clarification, however, since the assessment by the abiotics group ~as at variance on this point with the San Juan Ecology Study. The San Juan study showed surface erosion, mass wasting, and consequent effects on water quality and fluvial sediment yield to be mostly associated with summer showery rainfall, which is not affected by the winter cloud seeding. After further discussion with Dr. Leaf, it became obvious that, if the assessment were restricted to winter snowpack augmentation, the expected response in the above-mentioned categories with 20 percent augmentation would be less detectable. This would then leave forests as perhaps both the largest and most important setting in which responses of erosion, channel processes, and sediment yield to winter snowpack augmentation might be detectable and sometimes important. For summertime shower augmentation, the agricultural setting claims this preeminence and is also the setting in which the state of the measurement art is most advanced. Among the environmental issues, those of water yield and fluvial geomorphology are expected to show the most readily detectable responses in the largest number of settings, followed by mass wasting. However, with 20 percent augmentation this prominence would be weakened if summer shower augmentation in alpine settings were stricken from consideration. It should be noted that in those areas having unstable or sensitive stream channels, responses in fluvial geomorphology can be detected with 20 percent augmentation-regardless of setting. All the other issues have remarkably even scores, In general, the state-of-the-art of understanding is seen as weakest in avalanches, snow duration, erosion, sediment yield, and chemical water quality; and strongest in water yield and physical water quality. The abiotics group recommended that quantification of impacts on abiotic components should proceed by further application of the principles and analytical framework it had arrived at, and that these same factors should guide the selection of research priorities as shown in the sensitivity matrix. They also recommended that the interfaces between abiotic components and other components such as vegetation should be pursued through further development of the same analytic approach, 4 -;1 ,