Masthead: Kaweah Range

Sierra Nature Notes, Volume 6, January 2006

Sierra Nevada Climate, 1650–1850
Scott Stine
Department of Geography and
Environmental Studies
California State University
Hayward, California

Excerpted from Stine, Scott, 1996. Climate of the Sierra Nevada, 1650-1850. Chapter 2 (pp 25-30) in, Sierra Nevada Ecosystem Project, Final Report to Congress, v. 2: Assessments and Scientific Basis forManagement Options.

The Sierra Nevada in winter (January, 2005)

Introduction
Climate exerts a profound influence on landscape by determining the flux of both energy (solar radiation) and mass (rain, snow, and water vapor). If climate changes significantly, the landscape can be expected to respond geomorphologically, hydrologically, and biologically. These individual responses, in turn, can feed on one another, creating a cascade of landscape perturbations.

Around 1850, just as large numbers of Europeans descended on the Sierra Nevada for the first time, the region experienced a marked shift in climate, from the abnormally cool and moderately dry conditions of the previous two centuries (the “Little Ice Age”), to the relatively warm and wet conditions that have characterized the past 145 years. This climatic shift should concern land managers for two interrelated reasons: First, the landscape changes that have occurred since 1850 may not be entirely anthropogenic but rather attributable in part to the shift in climate. Second, the landscape of the immediate pre–gold rush period should not be considered an exact model for what the Sierra would be today had Europeans never colonized the region. Thus, attempts to restore “natural conditions” as part of an overall Sierra Nevada management plan should focus not on the pre-European landscape but rather on the landscape that would have evolved during the past century and a half in the absence of Europeans.

Using proxy climatic records, this paper explores the Sierra Nevada climate of the period 1650–1850 and compares it to that of the modern (post-1850) period. The focus is on climate at the decade to century scale, rather than on individual years or meteorological events. Emphasis is placed on records from lakes, glaciers, tree lines, and tree rings that can be resolved to time scales of multiple decades or less. Other types of proxy indicators, such as pollen and pack-rat records, while indispensable for illuminating multiple-century to millennial changes in climate, are not included in this analysis.

Climate Generalizations
Climate is not a landscape component as much as a landscape determinant. It exerts an overriding influence on such landscape components as vegetation (including its type, biomass, and distribution), hydrology (including the size, distribution, fluctuations, and water quality of lakes and rivers), soils (including their thickness, stability, and nutrient capacity), and landforms (including their rates of formation and loss). It also strongly influences other landscape determinants, the most important of which may be fire (including its location, frequency, and intensity).

Climate is inherently changeable, whether by the decade, century, or millennium. It is inherently variable, with some periods characterized by frequent and/or wide departures from the average and others by infrequent and/or narrow departures. And it is inherently site-specific, differing even over small areas depending on such variables as topography, slope orientation, vegetation cover, and elevation. In a range as high, extensive in area, and complex in topography as the Sierra Nevada, the variety of local climates is too extensive to enumerate here. The following generalizations can be drawn, however:

Climate in the Sierra, 1650–1850
Climate varies not only spatially but also temporally, with some periods being relatively wet and others relatively dry, some relatively cool and others warm. Putting aside for now the year-to-year and decade-to-decade variations in climate, it is possible to characterize the period from the mid-1600s to the mid-1800s as having been, by modern standards, abnormally cool and moderately dry. This interval was preceded by several centuries of cool and wet conditions and was followed by the relatively warm and wet conditions of the past 145 years. Evidence for these generalizations comes from several sources.

Mono Lake
Mono Lake, on the lee side of the central Sierra Nevada, receives its inflow from the Rush, Lee Vining, and Mill Creek drainages. Since 1941, much of this inflow has been diverted by the Los Angeles Department of Water and Power for domestic supply, forcing the lake to low levels. But for these diversions, the lake surface during the past century would have fluctuated within a narrow elevation interval (± 2 m [6 ft]) centered on about 1,958 m (6,423 ft) (P. Vorster, telephone conversation with the author, May 1995). This elevation is hereafter referred to as the “natural level” of the modern period. Around 1650, Mono Lake attained a high stand at 1,967.8 m (6,456 ft), 10 m (30 ft) higher than the calculated natural level of the modern period (Stine 1987, 1990). Radiometrically dated evidence for this high stand (and thus evidence for effectively wet conditions) is seen today in the form of rooted stumps, sedimentary sequences, and geomorphic stand lines. These same lines of evidence demonstrate that between 1650 and about 1840 effectively drier conditions drove Mono Lake to 1,948.9 m (6,394 ft)—9 vertical meters (29 ft) below the calculated “natural level” of the modern period. This low level, corresponding to a surface area approximately 79% that of the modern natural value, indicates that the effective inflow to Mono Lake prior to 1850 was, on average, less than 79% of the effective inflow of the period 1937–79 (Stine 1987, 1990).

Holocene shorelines of Mono Lake
(Click map to enlarge)

Owens Lake
Owens Lake is the natural sink for all eastern Sierra Nevada runoff south of the Mono Basin. Diversion of the Owens River (Owens Lake’s main feeder stream), first by irrigation interests in the Owens Valley and subsequently by the Los Angeles Department of Water and Power, has desiccated the lake, exposing the entire playa floor. Were it not for these diversions, Owens Lake since the early 1860s would have stood within a narrow elevation interval (±1 m [3 ft]) centered on about 1,095.5 m (3,594 ft). Such a lake would cover the now dry lake floor with up to 15.8 m (52 ft) of water (Stine 1994). Sequences of lake-transgressive and lake-regressive deltaic sediments exposed in the walls of the stream cuts adjacent to Owens Lake provide evidence that around the half-century 1600–1650 effectively wet conditions drove the shoreline to an elevation of 1,098.8 m (3,605 ft), creating a lake with a surface area approximately 110% that of the modern natural value. Effectively dry conditions prevailed during much of the ensuing two centuries, forcing the lake to elevations below 1,088 m (3,570 ft)—more than 7 m (24 ft) lower than the natural level of the modern period. This low stand represents a surface area approximately 77% that of the natural modern value, suggesting that effective inflow to the lake was more than 23% below the natural modern value (Stine 1994; Stine, unpublished data).

In summary, the closed lakes of the eastern Sierra Nevada are consistent in being dominated by declining levels and low stands during the period from the mid-1600s to the mid-1800s. In those two centuries the lakes attained elevations lower than those of the prior century (1550–1650) and lower than the “natural levels” of the twentieth century.

A comparison of Lyell Glacier, Yosemite National Park in 1903 (top) taken by G.K. Gilbert, and 2003 (bottom) taken by Hassan Basagic.
From Hassan Basagic Twentieth Century Glacier Change in the Sierra Nevada, California

Evidence from Sierra Nevada Glaciers
Following thousands of years of little or no glaciation, high elevation cirques of the Sierra Nevada experienced ice accumulation for several centuries prior to 1850 (Clark and Gillespie 1995; Curry 1969). This period of minor glacier advance (typically less than 2 km), first described in the Sierra by Matthes (1939), corresponds to the “Little Ice Age”—a period of cooling over much of the globe that began in the fourteenth or fifteenth century and continued through the middle of the nineteenth century (Grove 1988).

Based on the well-documented behavior of glaciers in the European Alps, Matthes (1939), speculated that these small ice bodies of the Sierra Nevada reached their maximum extent during the period 1850–55. Maps and photos produced by Russell (1885a, 1889) show that by the early 1880s the Lyell, McClure, and Dana Glaciers had begun to retreat from their maximum positions of the Little Ice Age, with the ice front lying several hundred feet (in the case of the Lyell Glacier) up the canyons from the terminal moraines. With the exception of a few years of net positive glacier balance (Curry 1969), this shrinkage, and the loss of many small ice patches, continued into the early decades of the twentieth century. Matthes (1939, 1942a, 1942b) noted that between 1933 and 1938 the Palisades Glacier thinned by 8.2 m (27 ft); that between 1931 and 1939 the East Lyell Glacier retreated 26.5 m (87 ft); and that between 1933 and 1941 the West Lyell Glacier thinned by 3.7 m (14 ft) and the East Lyell Glacier by 6.7 to 10.4 m (22 to 34 ft). Further shrinkage of the glaciers is evident from a comparison of the U.S. Geological Survey quadrangles from the late 1940s and early 1950s with those from the 1980s. Evidence thus indicates that the centuries prior to 1850 were abnormal in the context of Holocene climate, in that they favored ice accumulation in cirques of the high Sierra. Shortly after 1850 the glaciers began to retreat. With the exception of a few aberrant years, Sierran glaciers have experienced a net negative balance since that time.

Theoretically, this minor glaciation of the mid-sixteenth through mid-nineteenth centuries is attributable to some combination of increased precipitation (leading to greater accumulation) and decreased temperature (leading to less melting and sublimation). Since the lake level records presented earlier in this chapter are consistent in suggesting that climate was relatively dry during this period, it might be concluded, as a working hypothesis, that relatively low temperatures caused the advance of the ice. Various types of dendroclimatological evidence also comport with this hypothesis. The dendroclimatic record [see original article – ed], in fact, verifies that climate was both relatively cool and relatively dry during the centuries preceding the California gold rush.

Summary and Discussion
A combination of records from lakes, glaciers, tree rings, and tree lines in and adjacent to the Sierra Nevada indicates that, in general, the period from around 1650 to 1850 was characterized by anomalously cool, moderately dry conditions. After being driven to their highest levels in several millennia by effectively high Sierran runoff, Mono, Pyramid, and Owens Lakes began to fall around 1650. Physical, biotic, and historical evidence indicates that during the 1840s and 1850s these lakes stood well below their modern natural levels, leading to the inference that effective inflow was perhaps 23%–34% less than the modern value. By the early 1860s the lakes were rising toward their modern natural levels in response to increased effective runoff from the Sierra.

As the closed lakes of the eastern Sierra were falling to low levels between 1650 and 1850, glaciers were forming and advancing in the high Sierra, arguably for the first time during the Holocene (the postglacial period). (Note that the accumulation of ice in the cirques of the eastern Sierra Nevada played only an insignificant role in decreasing runoff from the Sierra during this period. The building of glaciers during the Little Ice Age is thus not, in and of itself, an explanation for the recession of the closed lakes.) Glacier increase, together with the hydrogen-isotope record from the White Mountain bristlecone pines and the tree-line depression in both the White Mountains and the Sierra, strongly suggests that the centuries prior to the California gold rush were the coolest of the past 8,000 and more years. The modern wasting of the glaciers, the upward expansion of alpine tree lines, and the hydrogen- isotope record all indicate that since 1850 the Sierra has experienced a marked warming.

Graumlich’s tree-ring record from the southern Sierra provides the most detailed view of variations in the latest Holocene climate. That record confirms that the period from 1650 to 1850 was generally dry, although it points up an important exception not evident in the lake or glacial records: the interval 1713–32 was anomalously wet. Graumlich’s work also provides corroboration that the period from 1650 to 1850 was, by both Holocene and modern standards, abnormally cool.

Using fire scarred trees in the Redwood Mountain area of Kings Canyon National Park, years of past occurrence and past fire frequencies were determined. Prior to 1875 fire frequency averaged 9 yr on west-facing slopes and 16 yr on east-facing slopes.
Photo © by Anthony Caprio NPS  

Implications for the Fire Regime in the Sierra Nevada
Based on an examination of burn scars in the tree rings of giant sequoias (Sequoiadendron giganteum) at five groves on the west slope of the Sierra, Swetnam (1993) reconstructed a 2,000-year-long fire history. Relating fire size and fire frequency to climate series derived from tree rings of giant sequoias and bristlecone pines, he documented a close decade- to century-scale positive relationship between summer temperature and fire activity (frequency and synchrony) and a close multiple-year-scale negative relationship between precipitation and fire activity. He tentatively attributes these relationships to high-frequency (years-scale) precipitation dependent changes in the moisture content of fuels and low frequency (decade- to century-scale) temperature-dependent changes in fuel production

Swetnam’s record indicates that throughout the period 1650–1850 fire frequency in the groves sustained its lowest level in 900 years, a result that would be expected, given the low temperatures of the Little Ice Age.

Equally expected would be an increase in fire frequency corresponding to the increase in temperature after 1850. This modern increase in fire frequency did not occur, however, probably for three reasons: decreased fuel loads due to sheep grazing, a decrease in ignition due to the demise of Native Californian culture, and fire suppression policies. Indeed, rather than increasing, fire frequency since 1850 has decreased to its lowest value of the past 2,000 years.

A fire may be recorded as a lesion in an annual ring when living cambium, usually on the margins of a catface, is injuring by the heat of the fire. Over time multiple injuries (fire scars) can occur.
Photo © by Anthony Caprio NPS

These findings underline the peculiarity of the modern fire regime in the Sierra Nevada: while the disparity between fire frequency of the modern period and that of the period 1650– 1850 is clearly large, the disparity between modern fire frequency and the frequency that would occur today absent European settlement is even larger.

Implications for Management of the Sierra Nevada
The period 1650–1850 is of great interest to Sierra Nevada land managers because it is the last interval in which Europeans exerted little if any influence on the Sierran landscape. It may be tempting to use the condition of the landscape as it existed during this two-century period as a model for what the Sierra would be today in the absence of Europeans. In a related way, it may be tempting to attribute all landscape changes that have occurred since 1850 to the agency of Europeans. There can be no question that many of the changes that have occurred since 1850 are attributable to the activities of Europeans. But it must be borne in mind that the European incursion closely coincided with a marked shift in climate and that some of the landscape change since 1850 may be, at least in part, attributable to that climate shift. The magnitude of the shift underscores its potential importance in instigating landscape change. In temperature, the shift was from the coldest century-scale interval of the Holocene, as indicated by the tree-line and glacier records, to one of the warmest periods of the past 4,000 years, as suggested by the recent upward movement of the tree line. In moisture availability, the shift was from moderate effective drought, as evidenced by the records of tree rings and lake levels, to the relative wetness of the present century—a century that appears, from the records of lake levels, to be the fourth-wettest of the past 4,000 years (Stine 1990) and that includes the third-wettest fifty-year interval (1937–86) of the past millennium (Graumlich 1993).

Thus it seems that, even if the European incursion had never occurred, the Sierra Nevada landscape of today would differ in significant ways from that of the immediate pre–gold rush period. With this in mind, attempts to restore “natural conditions” as part of an overall management plan should focus not on the pre-European landscape but rather on the landscape that would have evolved during the past century and a half in the absence of Europeans.

References

Further Reading

Stine, Scott, 1990.
Late Holocene fluctuations of Mono Lake, eastern California. Palaeogeography, Palaeoclimatology, Palaeoecology v. 78, pp 333-381(1990).

Mono Basin Clearinghouse

How has climatic variation influenced treeline dynamics in the past?

Andrea H. Lloyd

Assistant Professor, Department of Biology, Middlebury College

The Great Droughts of Y1K
Scott Stine, Ph.D
California State University, Hayward

Sierran Treeline Dynamics in a Changing Climate
by Andrew G. Bunn

PhD Candidate
Department of Land Resources and Environmental Science
Montana State University

Persistence of pikas in two low-elevation national monuments in the western United States
By Erik A. Beever, Ph.D.
Ecologist, U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331.

Estimated Ages of Some Large Giant Sequoias:
General Sherman Keeps Getting Younger

Nathan L. Stephenson, Ph.D

U.S. Geological Survey, Western Ecological Research Center, Sequoia and Kings Canyon Field Station.

USC Geology 150: Climate Change

 

 



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