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Seasonal Precipitation Fluctuations in the Western United States During the Late Nineteenth Century

Raymond S. BradleyDepartment of Geology and Geography, University of Massachusetts, Amhersi 01002

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Abstract

Early historical records for states west of 105°W were used to document precipitation variations during the latter half of the 19th century (1851–1890). Over 260 records of five years or more were used. Nineteenth century data were compared with more recent records, 1951–60 averages at the nearest comparable stations.

Winter precipitation was greater than 1951–60 averages over much of the western United States from at least 1865 to 1890. In many parts of the region this would have meant considerably more snow than in recent decades. Summers, 1870–90, were drier than the 1950's, though before 1870 this may not have been so. Fall precipitation amounts were relatively low for much of the late 19th century. Precipitation in California was below 1951–60 averages for most of the period 1851–1880, though winter months during 1861–1875 were above average. Well above average precipitation was recorded in California in the fall months of 1881–1890 and in the summer months of 1881–85.

Winter precipitation records in the Southwest show distinct peaks at approximately five-year intervals which are paralleled by equally marked troughs in winter records from the Northwest. Peaks in the South-west records and corresponding troughs in the Northwest occurred in 1854 or 1855, 1859, 1867 or 1868, 1873, 1378 or 1879, 1883 or 1884 and 1888 or 1889. The inverse relationship probably reflects changes in the latitudinal position of depressions crossing the west coast of the United States in different years, but the reason for the quasi-periodic nature of the pattern is not clear.

Abstract

Early historical records for states west of 105°W were used to document precipitation variations during the latter half of the 19th century (1851–1890). Over 260 records of five years or more were used. Nineteenth century data were compared with more recent records, 1951–60 averages at the nearest comparable stations.

Winter precipitation was greater than 1951–60 averages over much of the western United States from at least 1865 to 1890. In many parts of the region this would have meant considerably more snow than in recent decades. Summers, 1870–90, were drier than the 1950's, though before 1870 this may not have been so. Fall precipitation amounts were relatively low for much of the late 19th century. Precipitation in California was below 1951–60 averages for most of the period 1851–1880, though winter months during 1861–1875 were above average. Well above average precipitation was recorded in California in the fall months of 1881–1890 and in the summer months of 1881–85.

Winter precipitation records in the Southwest show distinct peaks at approximately five-year intervals which are paralleled by equally marked troughs in winter records from the Northwest. Peaks in the South-west records and corresponding troughs in the Northwest occurred in 1854 or 1855, 1859, 1867 or 1868, 1873, 1378 or 1879, 1883 or 1884 and 1888 or 1889. The inverse relationship probably reflects changes in the latitudinal position of depressions crossing the west coast of the United States in different years, but the reason for the quasi-periodic nature of the pattern is not clear.

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