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Yosemite Nature Notes 47(3) (1978)


SNOW—THE MISSING LINK

Jim Huning

Most persons who visited Yosemite last summer were struck by the moderate to low water conditions that existed throughout the Park. At times, visitors were even irate because Yosemite Falls were dry or showed only as a wet streak down the granite walls. Many visitors that I contacted at my campfire program on the California drought were aware of, and accepted, low water conditions in the Park and appeared to carry the ‘low water concept’ to their urban dwellings and practice conservation measures. I suspect that considerable mass media exposure of the drought has served to make this drought more ‘real’ to everyone than droughts that had occurred in the past. Perception of drought conditions varied as a function of geographic location and, not too surprisingly, occupation. A farmer or rancher from the central San Joaquin Valley was significantly more cognizant of low water conditions than the urbanite from, say, the Los Angeles Metropolitan area.

Winter precipitation during 1976-77 has gone down on the record books as the driest in California’s history. The visitor must realize, however, that droughts occurred in the past, and will occur again in the future. Certainly droughts in the past (1860’s, 1890’s, 1924, 1931) were of similar magnitude. The primary difference between those droughts and the present one is that with the large population,. agricultural and industrial bases that exist today, the perceptions and effects of drought conditions are much more dramatic. Indications are that we are entering a period of increasing precipitation variability.1 Such a situation implies increasing environmental stress on all biota. Is this a bad or negative situation, one that should have mitigating efforts placed against it? I think not. On the contrary, it will, and is, affording us a chance to observe and examine natural processes at work. One striking example has been the ‘bloom’ of the lodgepole needleminer moth (Evagora milleri). The casual visitor to Tuolumne Meadows could not help but notice the ‘rust’ colored appearance of the lodgepole pine (Pinus contorta var. murrayana), or the apparently dead lodgepole pines along the lower flanks of Mammoth Peak. Would the needleminer moth be as active if it were not for the meteorological conditions which brought on the great drought and associated mild winter conditions for the past several winters? Probably not.2 But, the needleminer moth has been with us before — to do us a service by thinning the forest — and will be with us in the future. If the higher elevations receive a harsh winter, the needleminer infestation will subside.

The winter of 1976-77 was so mild that every winter month in Tuolumne Meadows, October-March, recorded maximum temperatures above 50F (10C). The lowest daily minimum temperature occurred in March, -11F (-24C). Most minimum temperatures were above 0F (—18C), a temperature far too mild to kill the needleminer moth larvae.3

How dry was the winter past? Although our precipitation recording network is sparse and of questionable accuracy (in mountainous terrain), it appears that most watersheds within the Sierra Nevada received only from 30-60% of their normal precipitation.4 The water content of the Sierra snowpack amounted to only about 5% of the normal value on 1 May 1977.5 In other words, all runoff had occurred by 1 May. The following winter precipitation data illustrate the severity of the drought in Yosemite.

1976-77 Winter Precipitation
Park Headquarters (3,970’)South Entrance (5,120’)
RAINFALL(DEPARTURE)RAINFALL(DEPARTURE)
October.82"(-.78).71"(-1.32)
November.82(-1.58).81(-5.52)
December.10(-6.85).64(-7.50)
January2.00(-4.51)1.92(-6.31)
February1.87(-3.66)2.26(-4.83)
March1.85(-3.25)2.09(-4.30)
TOTAL7.46"(-20.63)8.43"(-29.78)
 
NOTE: All data given in inches
Source: U.S. Department of Commerce Weather Bureau

Although negative departures occurred each month, the departures were especially great in several months (e.g., December). October-March precipitation at Park Headquarters and South Entrance were 27% and 22% of normal, respectively. In addition, for the calendar year 1976, Park Headquarters received a total precipitation of 14.84 inches, or 22.3 inches below normal, while South Entrance received a total of 13.65 inches; a whopping 32.14 inches (below normal. Each annual total represents a precipitation amount only slightly greater than the average for Los Angeles, located in a semi-arid environment.

Yosemite, the Sierra Nevada, California and the western United States have experienced two very dry years. The question in everyone’s mind is, “What will the winter of 1977-78 bring?” By the time this note is in print the question will have been answered. The best analysis to-date (September, 1977) indicates the state will have a precipitation total anywhere from 70-80% of normal.

Such a value is not good, but it does represent a substantial increase over the disastrous winter of 1976-77. In order to alleviate the problems associated with the droughts of the last two years, the state needs several years of above normal precipitation. Let us all hope we have ‘bottomed’ out and the next few years will record normal or above normal precipitation amounts.

REFERENCES

1) James R. Huning. A VISUALIZATION OF SEASONAL AND ANNUAL PRECIPITATION VARIABILITY IN THE SOVIET UNION. Ph.D. dissertation, University of California, Riverside, 1976.

2) Tom Koerber, U.S. Forest Service entomologist studying the needleminer infestation in Yosemite National Park, personal communication.

3) Data furnished courtesy of Tom Koerber.

4) LOS ANGELES TIMES, 28 August 1977.

5) WATER CONDITIONS IN CALIFORNIA, REPORT NO. 4. California Cooperative Snow Surveys Bulletin No. 120-77, State of California, The Resources Agency, Department of Water Resources, 1 May 1977.



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