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<br />t"J'" ";, r, <br />...."J......;.J <br /> <br />. <br /> <br />. <br /> <br />2, Change in the Mean Flow over the record <br /> <br />The mean flow for the period 1974-93 at Archuleta is 104,377 Ac-ftlmonth, which is about 10% <br />higher than the mean flow for the full period of record. The trend in the mean monthly flow for the <br />Archuleta gage over the record is shown in figure 2 using lowess with a moving window of 20 years, The <br />mean flows recorded in the 1974-93 period are among the highest over the record. It is interesting to note <br />that this stream exhibits a sudden transition in the mean flow from wet to dry around 1945, stays in a <br />relatively dry state for nearly 30 years, before a sudden transition to a wet period near 1976. These <br />"climatic shifts" are similar to those observed in N. hemisphere temperature and temperature gradient <br />records by Jain et al (1997), and likely have their origin in large scale climate rather than basin hydrology. <br />Similar trends are noted at the Bluff gage. <br /> <br />o <br />o <br />o <br />o <br />o <br /> <br /> <br />Mean or 1974-93 record = 104 377 <br /> <br /> <br />o <br />o <br />o <br />o <br />~ <br /> <br />~ <br />u: <br />'" <br />" <br />'5 <br />.c <br />~ <br /> <br />-. _ _.n.. _ _.'. 00 _. 00 00 00 _ M~~Q.QUyl! r~99f~_ 'O_!l4.~Q4_ 00 _ 00 no _ _ _ moo 00 _u__ 00 m <br /> <br />o <br />o <br />o <br />o <br />0> <br /> <br />o <br />o <br />o <br />o <br />'" <br /> <br />1930 <br /> <br />1940 <br /> <br />1950 <br /> <br />1960 <br /> <br />1970 <br /> <br />1980 <br /> <br />1990 <br /> <br />Year <br /> <br />. . <br />Figure 2: Trends in the mean flow of the San Juan River at Archuleta identified lowess with a moving <br />window of240 months. The 1948-1975 period is marked by a protracted reduction of nearly 20% in mean <br />flow relative to the 1974-93 period. The period prior to 1945 has some similarity to the recent period. <br />There is nearly a 50% variation in the 20 year moving window mean over the record suggesting that 20 <br />year periods may show a high variability at the site. Flows are in Acre-feet/month. <br /> <br />May 25, 1997 <br /> <br />3 I <br />