Doctoral Dissertation Research: Paleohurricane Proxy Records from the Pacific Coast of Mexico

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To infer long-term patterns of tropical cyclone activity, it is imperative to collect and interpret data beyond the historical observational period. Paleotempestology is a relatively young science that studies past tropical cyclone activity mainly by means of geological proxy techniques. Paleotempestological research has been successfully conducted at many locations along the U.S. Gulf and Atlantic coasts and the pan-Caribbean region, but proxy records are notably lacking from the Pacific coast of Mexico. Doctoral student Thomas Bianchette under the supervision of Professor Kam-biu Liu will establish a centennial-to-millennial record of paleohurricane strikes from Jalisco and Guerrero on Mexico's Pacific coast using coastal lake-sediment proxies. The geomorphic setting of the study sites and the typical tracks and strengths of tropical cyclones in this region suggest that hurricane strikes will be identifiable in these sediments. In addition to using overwash sand layers as a storm surge proxy, this study will pioneer a new methodology using slopewash deposits and fossil pollen as supplementary proxies to detect indirect hurricane strikes resulting from coast-parallel storms that bring heavy precipitation but do not make landfall (i.e., limited storm surge). The methodology will be based on the hypothesis that increased storm activity during an active period on centennial timescales will result in a wetter climate, leading to a long-term vegetation response that can be detected in the pollen record. Recent storms that have caused a geological and/or biological imprint will be used as modern analogs to aid in interpreting older storm events in the sedimentary record. A geographic information system will be developed to visualize the relationship between historical storm tracks and climate conditions (especially El-Nino/Southern Oscillation), while remote sensing technologies will be used to determine the geomorphological and biophysical effects of recent hurricanes. We hypothesize that a longer return period will be found for tropical cyclones along this coast than for the U.S. Gulf and Atlantic coasts based on multi-millennial data, with northern areas (Jalisco) on Mexico's Pacific coast exhibiting a higher storm frequency than southern locations (Guerrero).This research promises to produce the first proxy records of tropical cyclone activity along the Pacific coast of Mexico. Because unraveling global tropical cyclone activity depends upon inter-basin correlations, proxy records of long-term activity regimes for the Eastern North Pacific basin are vital. The new methodology of using slopewash deposits and fossil pollen as supplementary proxies can advance paleotempestological studies by permitting the use of inland sites and detecting paleo-storm events that brought excessive rain but did not cause significant overwash processes. Furthermore, this study will have great societal relevance as historical tropical cyclone strikes along Mexico's Pacific coast have caused tremendous damage to society and infrastructure, including significant public health problems. Mexico's instrumental record of these storms is very short (since 1949), making long-term risk assessment difficult. Establishing more reliable estimates of hurricane return periods based on multi-centennial or millennial proxy records can help inform decision makers, thereby improving planning and mitigation policy.