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OD2273 ^PPE~'DIX A Explanation of RatinR System !I For each discrete component of the environment con- sidered as a Teceptor of an impact of precipitation management, numbered ratings for each of four characteristics aTe tabulated and presented imme- diately following the subject heading. The purpose of this tabulation is to facilitate comparison of the essential characteristics and their relative importance among the various receptor components, and to avoid tediously repetitious explanations in the text. The firat tabulated characteristic is the strength of the relationship between precipitation manage- ment and the environmental component under con- sideration, without reference to whether the impact may be beneficial, hannful, or neutral in value. The relationship 1s called strong if precipitation management controls most of the variance of the environmental component and weak if it is largely ineffectual as a control. The particular defini- tions used are: " o Ineffectual Precipitation management has no direct relationship with the environmental component and any indirect relationship is weak or disturbed. Correlation is not significant by classical tests. There may be speculation about possible effects but no con- sensus as to choice between alternative speculations. Vi2ry weak Precipitation management has a direct or indirect relarionship with the environmental component that can be traced with a signi- ficant degree of confidence; the correlation is significant by classical tests. However, con- trol of changes in the environ- mental component by precipitation management is subordinate to at least one other factor and usually to a number of other factors, either natural or artificial, so that precipitation management accounts for less than 20 percent of the variance. As a "lever of management," precipi- tation management is present but inconspicuous. 2 Moderately weak Precipitation management has a direct ar indirect relationship with the environmental component. more or less comparable in strength to other relationships governing changes in the compon- ent. It generally accounts for 20 percent or more of the total variance of the environmental component. but always less than 50 percent. ~ong the "levers of management. precipitation 3 Hoderately strong management holds rank subordinate to at least one other natural or artificial control, and usually to several. Precipitation management is the single most important determinant of variation of the environmental component, even though the combined effect of other controls may at times outweigh it. Among the "levers of management," precipi- tation management is the most influential, though other "levers" may be. and usually, are important. Precipitation management has greater influence on changes in the environmental component than any other factor. Among the "levers of management ,II it is the overriding one. The second tabulated characteristic estimates the potential value of the impact, whether good, bad, mixed. or indifferen~. A moderate, gentle rain breaking a summer drought might be seen as an unalloyed good for thirsty crops, but most impacts will be a mixture of good and bad, with one or the other predominating. Indifference characterizes some cases, such as that of a field from which the crop is newly harvested. The particular definitions used are: 17 Precipitation management nearly always causes a significant amount of beneficial change in the en- vironmental component. In a given setting, the component is in a situation to benefit f~om precipi- tation management more than 80 percent of the time during an operational period. Situations during a period when effects would be ha~ful are infrequent and relatively insignificant. Precipitation management fre- quently causes a significant amount of beneficial change in the environmental component, but there may also be frequent times when the benefit is inconsequential or there may be infrequent times when it is significantly harmful. The regular application of pre- cipitation management would affect the environmental component, on the whole. more beneficially than harmfully. In a given" set- ting, the environmental component is in a situation to benefit from precipitation management more than 50 percent of the time, and beneficial effects are, in general, more consequential than harmful effects. J/ FrDm U.S. Bureau of Reclamation. P rid f i 1 _ rag ammat c ra t env rorumenta impact statement far Project Skywater. In Press. 4 Very strong +3 Strongly benefic ia I +2 Moderately b6!neficial