A crop-based rainfall chronology for pre-instrumental record southern California

✍ Scribed by Lester B. Rowntree

• Book ID: 104640629
• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 913 KB
• Volume: 7
• Category: Article
• ISSN: 0165-0009
• DOI: 10.1007/bf00144173

✦ Synopsis

Although measured climatic records begin in California about 1850, agricultural records from the earlier Spanish period can be used to develop information about annual precipitation. This historical material should be used, however, only with a full understanding of the numerous cultural variables that influenced agricultural production. A study by Iynch in 1931, which is widely cited in the literature of Pacific Coast climate reconstruction, contains serious shortcomings because of incorrect assumptions about the Spanish agricultural system, and, more specificaUy, the amount of climatic information expressed in yearly harvest data. In this article, mission data are analyzed more rigorously to produce a revised annual rainfall index for southern California that encompasses most of the pre-instrumental record period.

1. Introduction

Historical materials are commonly used to reconstruct weather and climate for those periods pre-dating the measurement of meteorological parameters. These documentary sources include a diverse range of archival data, such as personal diaries, governmental reports, log books, and agricultural information (see, for example, Ingram et al., 1981;Ogilvie, 1984). However, shortcomings of these historical data are numerous, and the accurate and appropriate use of documentary sources involves a rigorous methodology for isolating reliable materials from those less faithful in conveying climatic information. When using agricultural information for climate reconstruction, for example, a comprehensive understanding of the settlement system's human ecology is necessary to sift out human variables and establish clear lines of causality between harvest data and climate. Once this is done, these historical data will often yield valid insights into past climates.

Instrumental climatic records begin in California about 1850, coincidental with the American period. Predating this, however, is almost a century of archival material from the Hispanic settlement era. More specifically, there is a wealth of detailed and accurate data on yearly agricultural activities from the Spanish missions that spread along the California coast from San Diego to San Francisco bay. Although human variables influence these agricultural data in many ways, there is, nonetheless, some climatic information contained in yearly harvest records; these can be refined into index values that convey useful information about pre-instrumental record rainfall for coastal California.

Lynch (1931) used these Spanish records in his rainfall index, a work that is widely referred to in the literature of Pacific Coast climatic reconstruction (see, for example,