Causes and Impacts of Rainfall Variability In Central Mexico on Multiple Timescales
The eastern sector of Mexico’s Trans-Mexican Volcanic Belt is a semi-arid region, where interannual rainfall variability is significantly stresses regional water resources and the livelihood of millions. The region is linked to a broader summertime rainfall regime known as the North American Monsoon (NAM). My dissertation uses multiple lines of evidence, from geochemistry to climate model output, to understand the causes of long-term droughts in this region.
My first dissertation chapter uses instrumental data to diagnose the causes of El Niño-induced droughts in Mexico. This work explores the mechanisms responsible for rainfall changes over Central Mexico during the developing versus decaying phase of an El Niño event. This study was the first to demonstrate the importance of moisture transport anomalies in reducing rainfall in highland Mexico during the decay phase of an El Niño.
My second dissertation chapter uses the oxygen stable isotope ratios (δ18O) of lacustrine carbonates as well as elemental geochemistry to reconstruct late Holocene drought in Central Mexico. This sub-centennially resolved record is the first to identify a significant dry interval in central Mexico from 1300-1100 cal yr. B.P., which may be temporally coherent with increased drought frequencies recorded on the Yucatan Peninsula. These results also hint at a role for climate change in regional prehistoric cultural changes at the nearby site of Cantona.
My third dissertation chapter explores impacts of late Holocene droughts on the terrestrial ecosystems in Central Mexico. I reconstructed past vegetation and fire dynamics from pollen and microscopic charcoal, and compared these data to our stable-isotope based climate reconstruction and regional archaeological records.
My fourth chapter is an exploration of the causes of centennial-scale across Mexico and Central America in the late Holocene. This work identifies the spatiotemporal patterns of late Holocene drought by synthesizing Mesoamerican proxy records. It presents a new hypothesis pointing to the role of changes in Atlantic circulation in causing droughts in Mesoamerica.
Finally, I synthesize the knowledge in each of the dissertation chapters and point to avenues of future research.