Doctoral Dissertation Research: Tree-Rings, Climate, and History in Central Mexico

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This research will use new tree-ring chronologies from Mexico in conjunction with historical records to reconstruct the history of extreme drought/wetness events and examine their impact on the environment and society in central Mexico for the last 300 to 500 years. Initial analyses of recently developed tree-ring chronologies from central Mexico indicate that tree growth there is strongly influenced by extreme climatic events such as drought. Several periods of abnormally poor growth apparent in the tree-ring record are coincident with drought-induced crop failures, famine, and attendant social disruption in central Mexico. The primary objective of this project will be to develop the first robust tree-ring reconstructions of precipitation in central Mexico, and use this data to validate and quantify historical records of extreme climate and related socio-environmental impacts. A variety of primary and secondary historical records will be consulted, including records from the Archivo General de la Nacion in Mexico City. Another objective of this project will be to reconstruct the timing of monsoon onset in central-southern Mexico and examine the consequences of abnormally early or late monsoon seasons. The timing and seasonal distribution of rainfall is an important factor in crop production in central Mexico, and several of our new tree-ring chronologies are well correlated with the onset date of the North American Monsoon System. The precipitation reconstructions will be developed using transfer functions between individual and regionally averaged tree-ring chronologies from central Mexico and precipitation data at both local and regional scales. The reconstruction of monsoon onset date will utilize the complete network of tree-ring chronologies in Mexico to derive the best relationship between the tree-ring record and onset date. Monsoon onset date will be determined using threshold analysis of daily precipitation data.Central Mexico is one of the most populous regions on earth. Reconstructions of past climate using tree-rings and other environmental data indicate that northern Mexico and the southwestern United States have experienced extreme climate fluctuations over the past 500 to 1000 years. There is an extensive body of historical documentation regarding the impact of climate on agriculture and society in central Mexico. But long, climate-sensitive tree-ring records have previously not been available for this region. The tree-ring reconstructions of precipitation and monsoon onset will represent new environmental records for the study of past climate and its impact on ecosystems and society in Mexico. The results of this research will be disseminated through conference presentations and journals, and by contribution to the International Tree-Ring Data Bank at the National Geophysical Data Center. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.