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Towards detecting anthropogenic changes in temperature and precipitation extremes

PI: Gabriele Hegerl
Institution: Duke University
Additional Investigators: Jesse Kenyon (Duke), Slava Kharin, Francis Zwiers Xuebin Zhang (Canadian Centre for Climate Modeling and Analysis), Peter Stott (Hadley Centre)
The aim of the proposed work is to detect anthropogenic changes in climate extremes. For temperature, a detection analysis for moderately extreme temperature (occurring once or several times a year) is presently underway, using fingerprints from CGCM2. Presently, we use an index based on percentile exceedances (based on revised observational indices, see Zhang et al., 2004), and additionally the index of the most extreme day of the year (see Hegerl et al., 2004). We propose to extend that analysis by using fingerprints of extreme temperature from the IPCC simulations. A multi-model ensemble of simulations of 20th century climate change will provide a fingerprint of changes in temperature extremes from the late 20th century. Additionally, fingerprints from individual models can be compared. For precipitation extremes, a detection approach using observations is presently not feasible due to differences in scale between station data observations and model data. Therefore we limit the analysis of precipitation extremes to comparing future changes in extreme rainfall between model simulations, to distinguish where models show consistent changes in mean and extreme rainfall, and where changes are inconsistent between models. This is to be done similar to the comparison in Hegerl et al., (2004).

This analyses uses similar data as the Kharin et al. project, but focus instead on intermediately extreme events (occurring once or several times per year) rather than on 20-year return values. However, both projects will closely collaborate.

Data requirements: Monthly average precipitation, Tmin and Tmax; daily data for these magnitudes from the second half of the 20th century, for rainfall also from 2040-2060.

Hegerl, G. C., F. Zwiers, S. Kharin and Peter Stott (2004): Detectability of anthropogenic changes in temperature and precipitation extremes. J. Climate, in press

Zhang, X., G. Hegerl, F. Zwiers and J. Kenyon (2004): Avoiding inhomogeneity in percentile-based indices of temperature change. Submitted to J. Climate.

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