In contrast with the rich and long historical records from the subtropical and tropical Mexico we know relatively little of its arid northwestern region highly sensitive to the North Pacific climate patterns. Here we will report new results from an ongoing historical reconstruction of climate variability and change in the Baja California Peninsula and southern Alta California for the last IV centuries. We are particularly interested in its impact on the socioeconomic processes of change and the on-going transformation of landscapes in this area through the agricultural practices and livestock production introduced during the XVII century by the missionaries. This work is a joint effort with a paleoceanographic and paleoclimatic project that seeks to recover and compare a series of historical and geological climatic and oceanographic records of sea surface temperature of the California Current, the productivity of its surface waters, and precipitation patterns on the adjacent continent, derived from several geochemical and faunal indices preserved in laminated sediments found in two coastal marine basins, tree-rings on land and written historical records.
Here we will present data on the historical crop yield and domestic livestock production for the period spanning from the founding of the first Mission in 1697 to the the closing of the last Mission in the 1840's. We will attempt to link the historical reconstruction of sea-surface temperature variability, droughts, coastal storms and fires on decadal timescales to their socioeconomical impact (famines, epidemics, plagues affecting crops) on agricultural production and demography . Our main objective is to find the relation between climatic events and variability to the societal and economical determinants of the productive activities of the population. The introduction of Old World type of agrarian practices in this region, characterized by low precipitacion patterns and the absence of a steady supply of water by main rivers, set up the stage for an economy highly dependent on the amount of rainfall and on the availability of arable land. European preferences for familiar foods such as bread and meat and the missionaries' opposition to the regular use of native foods led to inadequate diets and inefficient use of scarce water resouces. The demographic history during this time period exemplifies the intimate interplay between natural climatic events and human action: the role of epidemics, the effect of recurrent crop plagues and famines. Climate and culture largely determined the inability of mission settlements to reach long-term suffieciency.
Human-induced modifications of land and water use remained modest until the 1840's. While it is understood that humans are direct agents in the use and modification of the environment, human-induced modifications encompass both intended and unintended consequences: the introduction of European livestock and of foreign seeds and weeds had a major impact on native life forms. The extent and direction of these changes can further our understanding of the human causes and consequences of global change. During subsequent periods these modifications initiated during the first centuries of the colonization of the Californias set the stage for major transformations occuring during the present century.