WMOD00593 - Laserfiche WebLink

Home Browse Search

.....----......... - TELLURIDE. - IRONTON 00", AMES. ~~:FNE 0 ~U~KA GLADSTONE, , HERMIT SANTA MARIA , 0 · RESERVOIR " HE~MIT 7SE , , precipitation size events is related to changes in the type of synoptic activity causing precipitation in the area. Plant growth, soil erosion, and runoff may all be affected by changes in precipitation size events. For example, a high frequency of small rains during the growing season will be of more importance to plant growth than fewer larger rains, where soil water-holding capacity would soon be exceeded, resulting in rapid run-off. This aspect of climatic variability has been investigated for the San Juan area and results are presented in the "Analysis of precipitation data, San Juan area" section of this report. A comprehensive review of climatic change studies for the western United States as a whole is found in Bradley (1976). ANALYSIS OF PRECIPITATION DATA, SAN JUAN AREA Data Homogeneitr A preliminary step in analyzing climatic fluctuations involves testing data for homogeneity. The standard technique, double mass curve analysis developed by Kohler (1949), has been employed, but this has proved not to be wholly satisfactory. The technique demands a minimum of seven stations with an equal length of record and therefore does not allow testing the few stations with maximum record length which are funda- mentally of most interest. At present, therefore, o HORSEFLY PLACERVILLE . .OURAY 0.8 " ,. TROUT LAKE. . SILVERTON .RICO - - - - 0.9- -...... CASCADE .PLEASANT VIEW ',. ELECTRA LAKE. , , .YELLOW JACKET . DOLORES G r .CORTEZ MANCOS --.!... ._ --- DURANGO MESA VERDE- _ - . NATIONAL PARK - -. ...... "- FOR,"'"LEWIS ..... , 0.9 0.8 'IGNACIO " '\ . SAN JUAN ECOLOGY . KLINE o 5 I. ..1 10 I 15 I 20 25 30 I I 1 · Precipitation stations operative 1968 o Precipitation stations no longer in operation CUMBRES . Scole of Mi les Figure 6. Durango: Winter correlations, 1950-1968. data are presented without comment as to homogeneity and interpretation is mainly confined to features common to a number of stations. Further analyses are found in Bradley (1976). Examinations of Inter-Station Correlations Product-moment correlation coefficients were computed between 24 precipitation stations in the San Juan area for annual and winter precipitation amounts according to the formula: 1 L (a-a) (b-b) N r (J l'b where r is the correlation coefficient, N is the number of cases, a is each case in sample A, a is ~he mean of sample A, b is each case in sample B, b is the mean of sample B, and (Ja is the standard deviation of sample A, and (Jb is the standard deviation of sample B. In nearly all cases, inter station correlations were significantly correlated at the 5 percent level or better and in many cases at the 0.1 percent level or better, for example, see Figure 6. This indicates that the San Juan area responds fairly uniformly as a region to seasonal variations in precipitation. Thus key stations examined are likely to reflect 0.1% Significance Level .LOS PINOS PASS LAKE .CITY oCATHEDRAL .WAGON WHEEL GAP . PALISADE LAKE ...... ...... ........ WOLF CREEK PASS'" ...... tMMITVIL;:E ...... o PLATORO .VALLECITO DAM -...... ...... STATE TURKEYO EXPERIMENTAL FARM f PROJECT 47