I am interested in figuring out how warmer temperatures in the future will impact western North America. In collaboration with Julia Cole (my advisor), Jonathan Overpeck, and others, I am using proxy records of drought to examine the spatial patterns of North American aridity during the last 2,000 years. We are also using climate model output to understand potential mechanisms responsible for past droughts and possible behaviors of future droughts. Below are a few projects related to my PhD research.

Long-term drought variability in North America>>
My main research attempts to use a multi-proxy dataset to describe the range of drought variability in western North America during the last 2,000 years. Two important findings have come out of this project so far: one drought variance tends to increase at lower frequencies; and two at least some of this tendency arises as a by-product of autocorrelation and time. We are currently testing the (counterintuitive) possibility that variability at the highest frequencies may be fundamentally driving drought variability at the lowest frequencies.

This map shows the locations, resolution, and types of proxies currently being used for this analysis.

The Magnitude of Decadal Variability in North American Precipitation Records>>
Low frequency patterns of sea surface temperature (SST) variability are thought to play a large role in developing and sustaining North American drought. Since SST is strongly connected to North American precipitation regimes, it is generally assumed that precipitation must vary on similar decadal to multidecadal timescales and hence drive the drought patterns. But, does it? This figure shows the fraction of variance from 25N to 60N concentrated in periods from 2 to 50 years. Using it and other spectral analyses, we investigate the local importance of decadal signals in a gridded precipitation dataset (for more see: Ault, T.R. and S. St George, 2010).

Drought in Climate Models>>
Do global climate models capture the full range of drought variability in North America? To answer this question, we have analyzed output from the Community Climate System Model III (CCSM3) run at the National Center for Atmospheric Research (NCAR) as well as climate model simulations of the last 100 and 500 years run on a wide range of models used in the IPCC 4th Assessment. Our main findings are that CCSM3 (and other models) reproduce the 20th century spatial patterns of drought, but most models do not generally reproduce the tendency of drought variance to increase at lower frequencies. Manuscripts describing these findings are available upon request.

Intensified decadal variability in tropical climate during the late 19th century>>
How is decadal variability related to interannual El Nino/Southern Oscillation (ENSO) variability in the tropics? How does it change over time? Given the limited time coverage of instrumental records, we must turn to proxy records to answer these questions. Previous work has shown that corals act as reliable proxies for SST throughout much of the tropical ENSO region. Building on that research, we analyze the dominant frequencies in a network of coral d18O records. This analysis seems to suggest that 20th century alone does not sample the full range of ENSO variability (for more see: Ault et al., 2009.

Outside Links:
Paleo Perspective on North American Drought (NOAA)
NOAA Paleoclimatology
US Drought Monitor
LDEO/IRI Climate Data Library
(also click map on right)
www.weather.com