This paper describes some examples of historical climate reconstruction pertaining to California, USA, focusing mostly on winter climate given the expected strongest teleconnection signals for this season. Climatic data consist of early instrumental data from the US Army Surgeon General at military forts, observers of the Smithsonian Institution, the Signal Service, and some private observers.

Documentary (non-instrumental) data were also used in assessing extreme events. Original daily records of these data were carefully assessed for discontinuities from examining diurnal temperature ranges and daily precipitation amounts. The climatic reconstructions conducted were as follows: 1) winter precipitation time series for selected locations since 1850, particularly for Sacramento and San Francisco, 2) winter temperature time series for selected locations since 1850, and 3) analyses of an extreme flooding event in January 1862 and a landfalling tropical cyclone of September 1939. Results indicate distinctive wetter winters for central and northern California in the late nineteenth century, and some of these wetter years correspond to well-known very strong El Ni˜no events. Connections to weaker El Ni˜no and La Ni˜na events, however, are not clearly evident. The flood of January 1862 is considered unprecedented when compared to other floods of the last 130 years. The reconstruction of a landfalling tropical cyclone for September 1939 near Los Angeles suggests its intensity at just below hurricane strength

Mock, C. J.

English

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DOI 10.1393/ncc/i2005-10221-3IL NUOVO CIMENTO Vol. 29 C, N. 1 Gennaio-Febbraio 2006Some comments on reconstructing the historical climate ofCalifornia, USA(∗)C. J. MockDepartment of Geography, University of South Carolina - Columbia SC, 29208, USA(ricevuto l’1 Settembre 2005)Summary. — This paper describes some examples of historical climate recon-struction pertaining to California, USA, focusing mostly on winter climate giventhe expected strongest teleconnection signals for this season. Climatic data consistof early instrumental data from the US Army Surgeon General at military forts,observers of the Smithsonian Institution, the Signal Service, and some private ob-servers. Documentary (non-instrumental) data were also used in assessing extremeevents. Original daily records of these data were carefully assessed for discontinu-ities from examining diurnal temperature ranges and daily precipitation amounts.The climatic reconstructions conducted were as follows: 1) winter precipitationtime series for selected locations since 1850, particularly for Sacramento and SanFrancisco, 2) winter temperature time series for selected locations since 1850, and3) analyses of an extreme flooding event in January 1862 and a landfalling tropicalcyclone of September 1939. Results indicate distinctive wetter winters for centraland northern California in the late nineteenth century, and some of these wetteryears correspond to well-known very strong El Nin˜o events. Connections to weakerEl Nin˜o and La Nin˜a events, however, are not clearly evident. The flood of January1862 is considered unprecedented when compared to other floods of the last 130years. The reconstruction of a landfalling tropical cyclone for September 1939 nearLos Angeles suggests its intensity at just below hurricane strength.PACS 92.60.Ry – Climatology.PACS 92.60.Wc – Weather analysis and prediction.PACS 93.30.Hf – North America.PACS 01.30.Cc – Conference proceedings.1. – IntroductionThe state of California, USA possesses some of the longest documentary and earlyinstrumental climatic data for western North America, well before the modern (twentieth(∗) Paper presented at the Workshop on “Historical Reconstruction of Climate Variability andChange in Mediterranean Regions”, Bologna, October 5-6, 2004.c© Societa` Italiana di Fisica 5556 C. J. MOCKcentury) record. Although extensive temporal coverage is generally less than 200 years,English language materials are particularly dense spatially after 1860 especially for cen-tral California, with some site-specific data being plentiful back to the late 1840s. Thesedata provide important information on verifying climatic reconstructions from tree-ringdata, examining spatial variations of climate in response to teleconnections such as ENSO(El Nin˜o-Southern Oscillation) and the PDO (Pacific Decadal Oscillation), assessing ex-treme meteorological events such as floods and snowstorms, and reconstructing the lengthof the growing season. This paper describes the data and some examples that are avail-able for historical climate reconstructions on California, focusing on nineteenth centurywinter climate given the strongest teleconnection signals for this season.2. – Nineteenth century dataThe earliest known systematic meteorological data for California were recorded byRussian settlers at Fort Ross from 1838-1842 [1]. Although fragments of records frommariners exist thereafter, continuous records generally did not resume until 1847 withweather observations recorded at Monterey, California and soon thereafter at the Presidioin San Francisco [2]. Thus, most weather observations for California prior to 1849 needto rely on non-instrumental documentary evidence. The instrumental observations wereunder the supervision of the US Army Surgeon General, stating temperature, prevalentwind direction, precipitation amounts, wind speed on a numerical scale from 0–10, andcloudiness on a numerical scale (0–10) [3]. Occasional records also included barometricpressure. The Smithsonian Institution initiated a national network during the early-mid nineteenth century as well, whereas some observers in California contributed databeginning in the 1850s. In addition, some weather enthusiasts also kept daily weatherrecords [4], and some of these daily records were published in local newspapers. Theseinclude records by Thomas Logan of Sacramento (1851-1867), Thomas Tennent of SanFrancisco (1849-1888), and Henry Gibbons of San Francisco (1850 to through the 1880s).The United States Signal Service set up a national-scale network in 1871, it being theforerunner of the US Weather Bureau, which was established in 1891 and include first-order weather stations such as San Francisco, Los Angeles, and San Diego. These earlyinstrumental data have to be carefully screened for data quality [5,6] . Temperature dataproblems include different routine fixed observation times that affected the compatibilitywith modern data, and by different thermometer exposure situations involving azimuth,shelters, and building material [6,7]. Corrections on this averaged temperature data fromfixed observation times to convention al maximum/minimum averages are clearly possiblefrom using modern hourly temperature data, but to date no such comprehensive correc-tions have yet been performed. Precipitation data problems include the conversion ofsnowfall to liquid, some high placements of rainfall gauges (e.g., 240 cm high and rooftop)that caused lower liquid accumulation due to increasing wind speeds [8], and gaps in time(sometimes several days or more) when precipitation gauges were actually measured thatmay result in evaporative loss of water. This underestimation of precipitation generally ismore apparent in cold-season precipitation [9]. Other problems concerning the accuracyof 19th century precipitation records include changes in the environment surroundingprecipitation gauges and in instrumentation. However, similar problems are also evidentin modern National Weather Service COOP (Cooperative) precipitation records, andno reasons exist to suggest that 19th century data possesses greater problems. Precip-itation data can also be expressed in precipitation frequency instead of magnitude, asthese reconstructions can often be directly compared with modern climatic data [10].SOME COMMENTS ON RECONSTRUCTING THE HISTORICAL CLIMATE ETC. 57Fig. 1. – Locations of weather stations in California with continuous data from 1872-2003.Stations with names and the principal components are discussed more in the text.Precipitation frequencies may also more accurately reflect homogeneous responses tosynoptic-scale atmospheric circulation [11]. Exactly-dated non-instrumental documen-tary records such as diaries, ship logbooks, annals, and newspapers are important butoften overlooked supplements to instrumental records, filling important temporal andspatial gaps, particularly concerning reconstruction of precipitation frequencies [10, 12].The documentary materials, however, cannot be taken at face value. Original sourcesshould be used as much as possible because typescripts can provide erroneous editedinformation. Written descriptions of climate may also reflect individual biases based ondiarists’ personal background and particular motivation for writing. Thus, a thoroughknowledge of the written materials, diarists, a historical background of the time periodi n question, and past climatic perceptions must be analyzed. Historical methodologies,such as content analysis, enable quantitative assessments of past climate by analyzingthe vocabulary of weather descriptions.3. – Some examples of California historical climate reconstructions3.1. Winter precipitation. – A principal components analysis with a Varimax rotationwas conducted on seasonal winter (December-February) precipitation data for 32 Califor-nia stations from 1872-2003 (fig. 1). This procedure was conducted to assess the regionalhomogeneity of precipitation patterns in California. The highest salient (significant)58 C. J. MOCKFig. 2. – Winter (December-February) precipitation at selected locations from 1850-2003.loading for each station was mapped relative to its related principal component. Threeprincipal components were extracted from the analysis. The first principal componentexplains 35.4% of the variance, and all but three of the stations have a salient loadingrelated to this component. Most of the loadings are less than −0.800 (higher absolute val-ues), thus indicating that California seasonal winter precipitation is quite homogeneousin response (fig. 1), although clearly individual magnitudes can vary spatially due totopography and from year-to-year. The second principal component explains 9.8% of thevariance, and salient loadings are evident for only three stations: Yuma, San Bernardino,and San Diego. A third principal component was extracted that explains 5.0% of thevariance. Its strongest loadings relate to some of the central California coastal stations,perhaps related to land/sea breeze processes. No stations exhibited salient loadings re-lated to this component. Several time series of winter precipitation were constructed toillustrate temporal variability through time. Available daily nineteenth century precipi-tation data for San Francisco, Sacramento, Los Angeles, and San Diego (in manuscriptand microfilm forms) were carefully screened for data quality. Higher daily precipitationfrequencies mostly correspond with smaller precipitation amounts, thus generally indi-SOME COMMENTS ON RECONSTRUCTING THE HISTORICAL CLIMATE ETC. 59Fig. 3. – Winter (December-February) precipitation at Los Angeles and San Diego from 1850-2003.cating satisfactory quality. Most of the daily nineteenth century precipitation data forStockton have still not been located, thus values were taken from Alexander McAdie’scompilation [13] and carefully compared with other stations. The time series of winterprecipitation for San Francisco and Sacramento exhibit similar trends from 1850-2003(fig. 2). Increased decadal variability is evident for much of the twentieth century, whilestronger interannual variability is evident prior to 1890. Of interest, more frequent win-ters with higher precipitation are evident for much of the 1860s-1880s as compared tothe recent century. Higher amounts of winter precipitation during 1878 and 1891 mayrelate with very strong El Nin˜o events as reconstructed by historical evidence in SouthAmerica [14], but of note there are numerous winters where low amounts of Californiawinter precipitation do not relate with medium-to-strong reconstructed El Nin˜o events.Some of the dry winters may relate with La Nin˜a events, though more research is neededto closely compare California reconstructions with La Nin˜a proxy reconstructions fromtree-rings. The time series of winter precipitation for Stockton is mostly similar to thoseof San Francisco and Sacramento, but it has a distinctively drier period from 1870-1900,perhaps due to lower data quality. All three records illustrate that the winter of 1851is the driest in the last 153 years. Conversely, the winter of 1862 is clearly the wettest,with most of the precipitation occurring in January (this event is described more insubsect. 3.3).The Los Angeles record, in which high quality data are presently limited back to 1872,illustrates increased decadal variability in the 1900-1960 (fig. 3). Its winter interannualvariability, however, shows different years with high and low values compared to therecords further north. The San Diego record, in contrast, exhibits more interannualvariability throughout most of the record, with more marked variability of wet and drywinters from the 1870s through the 1890s. It also illustrates a distinctively dry periodfrom 1950 to 1990.60 C. J. MOCKFig. 4. – Winter (December-February) temperatures at selected locations from 1850-2003.3.2. Winter temperature. – Some time series of winter temperature are presented forSan Francisco, Sacramento, and San Diego (fig. 4). These records have been correctedfor fixed observation times to be consistent with post-1871 records that have averagesbased on maximum/minimum temperatures. However, the time series of nineteenthcentury data presented here have not been corrected for exposure problems. All threetime series illustrate rising trends since 1940, reflective of the urban heat island. The SanFrancisco temperature time series, relying mostly on the Thomas Tennent record priorto 1871, demonstrates some relatively cold winters from 1858-1862. Close inspection ofother daily San Francisco records (e.g., from the Gibbons, Ayers, Presidio and AlcatrazIsland records) immediately available suggests that these winters were likely quite cold,including the winter of 1859. The nineteenth century San Francisco record does notcompare closely with that for San Diego as well as for Sacramento, and this result mayreflect the fact that temperatures at San Francisco are generally not homogeneous inrelation to regional California climate.3.3. Examples of extreme events. – Documentary and instrumental data are crucialto integrate together in order to reconstruct extreme weather events in California, suchSOME COMMENTS ON RECONSTRUCTING THE HISTORICAL CLIMATE ETC. 61Fig. 5. – Time series of daily data for the winter of 1861-62 for San Francisco, California. Datawere recorded by Thomas Tennent.as extreme flooding events. This aspect is particularly important, as some reconstructedextreme events are clearly “unprecedented” when compared to what we perceive as “nor-mal” and there is a need to improve probabilistic models. Society may not properlyprepare for extreme events if it bases their likelihood on only a particular timeframe(e.g., last 50 years) [15]. One particular event that is currently still not that accuratelyreconstructed at a statewide level is a flooding event in January of 1862, as much ad-ditional documentary and instrumental data need to be extracted from the archives.Current general estimates of the magnitude of flooding suggest that it is clearly by farthe most serious flood ever witnessed in northern and central California [16], and docu-mentary (non-instrumental) data suggest that extreme flooding was extensive throughoutthe California Central Valley. This event also is evident into the Pacific Northwest andeastward through Nevada into Utah [17]. Daily meteorological information found inthe Daily Alta California newspaper for San Francisco reveal the prominent fluctuationsduring the winter of 1861-62 (fig. 5). Relatively warm conditions in December were re-placed by a series of persistent strong storms that brought cold air into the region. Thesestorms brought more than 50 cm of rainfall within two weeks; the rainfall exceeded what62 C. J. MOCKis normally experienced in San Francisco for an entire year. Z-scores reveal that theJanuary 1862 event is almost 4 standard deviations above the mean when comparingrainfall values with the entire San Francisco record (J. Goodridge personal communica-tion). Numerous other meteorological stations in California reveal similar results, butsome display somewhat smaller z-scores. These smaller z-scores likely reflect poorer dataquality in some 1862 weather records, as precipitation was normally underestimated. Alandfalling tropical cyclone in southern California in late September 1939 is a ratherunique extreme event that also deserves a more detailed reconstruction. The authorfound evidence in California archives of a sea-level pressure value around 993 hPa off SanDiego early on September 25, 1939. Extrapolating this value to an estimated positionof the tropical cyclone center suggests a central pressure value that could be as low asabout 990 hPa [18, 19]. This pressure value suggests a maximum strength of a tropicalcyclone at about 55-60 knots. Documentary evidence of tropical cyclone damage in theLos Angeles area examined to date, however, suggests that the tropical cyclone was justbelow hurricane strength. The evidence also clearly shows that much of the damageoccurred earlier on September 25, thus suggesting that the tropical cyclone moved fasterthan as illustrated on the track previously constructed by others to date [18]. The $2million (US dollars) in damages from this storm would likely be over $100 million todayif it occurred, given higher population densities along with inflation adjustments.4. – Closing remarksSerious comprehensive attempts to reconstruct the nineteenth century historical cli-mate of California has never be en conducted. However, examples discussed in this paperdemonstrate that the late nineteenth century contains characteristics of climate variabil-ity that differed from the last 100 years, thus deserving attention. Historical climaticreconstructions have important information that can be used to verify climatic recon-structions from tree-ring data and other high-resolution paleoclimatic proxies. Detaileddata are also available to study climatic hazards down to block-by-block resolution, suchas the extreme flood of 1862. Clearly, examples in this paper illustrate that the spa-tial density of daily historical climate data is plentiful for central California and otherscattered areas of the state back to the 1840s concerning English documents. Spanishdocuments can additionally extend the record further back for southern California [20].Nevertheless, any future historical climate study for California will require vast amountsof time—this includes intensive archival data collection for newly discovered meteoro-logical and documentary materials, digitization, as well as the correction of nineteenthcentury instrumental data that is currently available.∗ ∗ ∗I gratefully acknowledge Jim Goodridge for comments and sharing his Californiadata, and to Mike Chenoweth for his comments on historical climatology. The collec-tion of some archival materials was made possible by NSF Grant BCS-0349986.REFERENCES[1] Chernykh E. L., Pacific Historian, 11 (1967) 10.[2] Darter L., List of Climatological Records in the National Archives (National Archives,Washington, D.C.) 1942.SOME COMMENTS ON RECONSTRUCTING THE HISTORICAL CLIMATE ETC. 63[3] Lawson T., Meteorological Register for twelve years, from 1843 to 1854 (War Department,Washington, D.C.) 1855.[4] Fleming J. R., Meteorology in America 1800-1870 (The John Hopkins University Press,Baltimore) 1990.[5] Bradley R. S., Precipitation History of the Rocky Mountain States (Westview Press,Boulder) 1976.[6] Chenoweth M., J. Clim., 6 (1993) 1787.[7] Chenoweth M., J. Clim., 5 (1992) 1172.[8] Sevruk B., Int. Assoc. Hydrol. Sci. Publ., 164 (1987) 477.[9] Mock C. J., Climatic Change, 44 (2000) 173.[10] Mock C. J., Climatic Change, 18 (1991) 37.[11] Woodhouse C. A. and D. M. Meko, J. Clim., 10 (1997) 2663.[12] Baron W. R., Agricultural History, 63 (1989) 7.[13] McAdie A., Climatology of California (U.S. Department of Agriculture, Washington,D.C.) 1903.[14] Ortlieb L., in El Nin˜o and the Southern Oscillation, edited by H. F. Diaz and V.Markgraf (Cambridge University Press, Cambridge) 2000, pp. 207-295.[15] Stockton C. W., Climatic Change, 16 (1990) 173.[16] McGlashan H. D. and Briggs R. C., U.S. Geological Survey Water-Supply Paper, 843(1939).[17] Larson A. K., I was called to Dixie (Deseret News Press, Salt Lake City) 1961.[18] Smith W. P., The effects of eastern North Pacific tropical cyclones on the southwesternUnited States (National Weather Service, Salt Lake City) 1986.[19] Ho F. P., Su J. C., Hanevich K. L., Smith R. J. and Richards F. P., Hurricaneclimatology for the Atlantic and Gulf coasts of the United States (National Weather Service,Silver Spring) 1987.[20] Rowntree L. B., Climatic Change, 7 (1985) 327.

Some comments on reconstructing the historical climate of

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Some comments on reconstructing the historical climate of California, USA

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