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<br />ISSUES <br />Precipitation (augmented precipitation) is the system which drives the <br />abiotic system. It is for this reason that in a process oriented approach <br />to abiotic impact the precipitation (augmented precipitation) input must be <br />expressed in terms of amount, intensity, frequency, duration, form, and in the <br />case of rainfall, drop size spectra. Of these, the first three are considered <br />to be the most generally important. <br />One of the first tasks undertaken was the summarization of issues <br />pertinent to the abiotic impacts that might occur as a result of intentional <br />precipitation augmentation. These issues have been divided into two basic <br />categories -- on site issues and off site issues. The term "on site" refers <br />to those issues which are pertinent at the point where the precipitation <br />(augmented precipitation) first reaches the surface. The "off site" termin- <br />ology refers to those issues that are pertinent to the routing of the <br />precipitation (augmented precipitation) and subsequent streamflow. <br />In order to objectively evaluate the potential impacts of weather modi- <br />fication on abiotic systems the concept of levels of consideration has been <br />introduced. Three levels are defined. They include (Figure 1) Atmospheric <br />Level, Precipitation Level, and River or Streamflow Level. <br />Atmospheric Level <br />The atmospheric is perhaps the most basic and important evaluation level, <br />since it deals with the precipitation process itself. However, evaluation at <br />this level requires study of the complex interactions of atmospheric properties <br />and involves a high level of technology. The aircraft and also sophisticated <br />ground systems needed to collect and analyze atmospheric data require large <br />investment of money, time, and skills. Accordingly, knowledge of atmospheric <br />or cloud physics has not entirely kept up with the need to determine the basic <br />abiotic processes that are affected by weather modification. <br /> <br />~ <br /> <br />~ <br /> <br />ti" <br /> <br />46 <br />