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<br />Recommendations for Use of the llIA Methods <br /> <br />During development of the IRA method, a longer list of statistical attributes was consolidated <br /> <br />to minimize the number of computations and to reduce redundancy, while at the same time <br /> <br />retaining as much sensitivity to different forms of hydrologic alteration as possible. The IIIA <br /> <br />. ..m"":~o <br />groups of statistics are robust in their ability to quantitatively describe alterations peculiar to- <br /> <br />,; "'IeVI1, <br />specific human influences such as flOod control.' However, users must bear in mind the riskof , "".1 <br />, , , , ,,' :iltw"1ii~#: ' <br />losing informationabout:characteristics of-hydrologic alteration when rehitive differenCeS~;;.~~;.:;t <br />..o;~.{. <br />averaged across attributes within IRA groups (Suter 1993). We therefore strongly recOmmend"., <br />tC!l!! <br />that IHA results be presen~ in the full IRA scorecard format (e.g., as shown in TablesT~ ,. <br />. - ~'-'. " <br /> <br />.-. . . . '. ." .,..<',:,"., ',".;..<:~~ <br />4) to retain information about the specific hydrologic alterations associated with the ,,~'. ' <br /> <br /> <br />.', " <br />. .. - _ _. _ .i.. " ~;:'_' ..Ii! <br />perturbation under investigation. Reporting the full suite of hydrologic attributes wilralsij;,;~ <br /> <br />, ",;,.~,,,.; <br />enable investigators to explore relationships between individual attributes and biotic 'reSponses~;~';;f. <br />. -:"';T{;~t~</':-:' <br /> <br />This caution about lumping hydrologic attributes into IHA groups and averngiOg reSUlts '.,. <br />;~ <br />within groups should not inhibit exploration of the relationship between overall group averages <br /> <br />and specific typeS of human impacts such as reservoir operations, ground water pumping, <br /> <br />:.:;,;:rt'ln.l <br /> <br />,~ ~n:~:"$fD <br />timber harvest, or urbanization. In fact, such integrative analysis is urgently needed to enable <br />...t~.- .", <br />" .,., . :+..."a~:,'. ' <br />ecosystem managers to better assess or anticipate the impacts of certain land and water uses;'c;;~'.;. <br /> <br />The sensitivity and robustness of individual IRA parameter~ and IHAgroup~ to a'~id~~~l~il~;':~ <br /> <br />of human impacts in different bioregional settings remains to be tested. '!illlfJ~ii';';~ <br />;';; ,..!Ji;I. ." <br /> <br />- '. ~-. <br /> <br />.,oi~~;:i;A . <br /> <br />,"~~ <br /> <br />23 <br /> <br />