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<br /> <br />· / / 'OUOAY 2L k~~iy <br /> <br />TELLURIDE. 0 'CDNTON / <br />{AMES. ~~:~E 0 ~REKA <br />GLADSTONE <br />TROUT LAKE. ~ <br />~ SILV~RTON <br /> <br />.RICO~ <br /> <br />o <br />HORSEFLY <br /> <br />" <br />.PLEASANT VIEW <br />, <br />.YELLOW JACKET <br />OO~OOES"'" <br /> <br />MANCOS <br />· '35 <br /> <br />.CORTEZ <br /> <br /> <br />DURANGO <br />. <br /> <br />. <br />MESA VERDE <br />NATIONAL PARK <br /> <br />. <br />KLINE <br /> <br />.LOS PINOS PASS <br /> <br />oCATHEDRAL <br /> <br />.WAGON WHEEL <br />GAP <br /> <br />35~ <br /> <br />.VALLECITO <br />DAM <br /> <br />WOLF CREEK <br />PASS <br /> <br />tMMITVILLE <br />o <br />PLATORO <br /> <br />STATE <br />TURKEYo <br />EXPERIMENTAL <br />FARM <br /> <br />l <br /> <br />IG:ACIO 30% <br /> <br />o 5 10 15 20 25 30 <br />I. ..1 I I I I <br /> <br />...- <br />~ JUAN ECOLOGY PROJECT <br /> <br />· Precipitation stations operative 1968 <br />o Precipitation stations no longer in operation <br /> <br />CUMBRES <br />. <br /> <br />Scale of Miles <br /> <br />Figure 8. Winter coefficient of variation, 1950-1968. <br /> <br />Seasonal coefficients of variation for selected <br />stations between 1914 and 1968 are given in Table 2a. <br />For all stations, except Durango, winters (November <br />to March) exhibit the lowest variability of precipi- <br />tation. If the stations are examined on an ele- <br />vational basis an interesting grouping is apparent <br />(Table 2b). For stations over approximately 2732 m <br />(9000 feet) spring precipitation (April, May) shows <br />less variability than stations between 2438 and <br />2743 m (8000 and 9000 feet) and much less variability <br />,than stations below 2438 m (8000 feet). This pre- <br />sumably reflects the.persistence of winter con- <br />ditions into these months at higher elevations. For <br />most stations the highest variability of precipita- <br />tion occurs in the transitional seasons, spring and <br />fall. <br /> <br />Precipitation variability, like total precipitation <br />amounts, is clearly subject to change over time <br />(Figure 9 and Table 3). In general, winter variabil- <br />ity is seen to be uniformly less in recent years <br />than earlier in the record and this may partly <br />account for the changing correlation fields over time <br />already noted. <br /> <br />Changes in the coefficient of variation for summer <br />precipitation do not show the coherence of the <br />winter seasons. Some stations show very large <br /> <br />decreases in variability, other show increases. <br />In view of the more convective type of storm <br />activity in the summer months, this result is <br />not surprising. Neither season shows any clear <br />spatial pattern of change in variability. <br /> <br />The Contribution Of Winter Precipitation To <br />Annual Precipitation Totals <br /> <br />For a number of stations, winter precipitation was <br />examined as a percentage of the annual total <br />(Figure 10). This illustrates clearly that the <br />contribution of winter precipitation to the annual <br />total is consistently below normal for the three <br />drought periods noted by Thomas (1959) for <br />"Pacific border" areas. Analysis of the pre- <br />dominant synoptic types during these periods may <br />shed light on the reasons for such a pattern. <br /> <br />Precipitation-Elevation Relationships <br /> <br />Precipitation-elevation relationships indicate a <br />regression relationship (r=0.76, 0.1 percent <br />significance level) in which mean annual precipi- <br />tation increases approximately 2.5 cm for each <br />100 m increase in elevation (approximately 3 inches <br />per 1000 feet). It should be noted that stations <br /> <br />49 <br />