Cool-season precipitation in the southwestern USA since AD 1000: comparison of linear and nonlinear techniques for reconstruction

New Mexico Neural Network Precipitation Reconstructions Cool-season precipitation in the southwestern USA since AD 1000: comparison of linear and nonlinear techniques for reconstruction
International Journal of Climatology
Volume 22, Issue 13, pp. 1645 - 1662, 15 November 2002.


Fenbiao Ni1, Tereza Cavazos2,3, Malcolm K. Hughes1, Andrew C. Comrie2, and Gary Funkhouser1
1 Laboratory of Tree-Ring Research, The University of Arizona, Tucson AZ 85721
2 Department of Geography and Regional Development, The University of Arizona, Tucson AZ 85721
3 Departamento de Oceanografía Física, CICESE, Mexico

ABSTRACT:
A 1000 year reconstruction of cool-season (November-April) precipitation was developed for each climate division in Arizona and New Mexico from a network of 19 tree-ring chronologies in the southwestern USA. Linear regression (LR) and artificial neural network (NN) models were used to identify the cool-season precipitation signal in tree rings. Using 1931-88 records, the stepwise LR model was cross-validated with a leave-one-out procedure and the NN was validated with a bootstrap technique. The final models were also independently validated using the 1896-1930 precipitation data. In most of the climate divisions, both techniques can successfully reconstruct dry and normal years, and the NN seems to capture large precipitation events and more variability better than the LR. In the 1000 year reconstructions the NN also produces more distinctive wet events and more variability, whereas the LR produces more distinctive dry events. The 1000 year reconstructed precipitation from the two models shows several sustained dry and wet periods comparable to the 1950s drought (e.g. 16th century mega drought) and to the post-1976 wet period (e.g. 1330s, 1610s). The impact of extreme periods on the environment may be stronger during sudden reversals from dry to wet, which were not uncommon throughout the millennium, such as the 1610s wet interval that followed the 16th century mega drought. The instrumental records suggest that strong dry to wet precipitation reversals in the past 1000 years might be linked to strong shifts from cold to warm El Niño-southern oscillation events and from a negative to positive Pacific decadal oscillation.

DATA:
Download the reconstructed Climate Division Precipitation data from the WDC Paleo Archive.
or click a Division on the maps below for time series plots and data for the divisional reconstructions.

Additional information and analysis on this research is available from the
CLIMAS (Climate Assessment for the Southwest) website.

Many of the tree ring chronologies utilized in this study are available from the International Tree Ring Data Bank.
Instrumental Climate Division Precipitation Data is available from the National Climatic Data Center.

To read or view the full study, please visit the Wiley InterScience website.
It was published in International Journal of Climatology, Volume 22, Issue 13, pp. 1645 - 1662, 15 November 2002.
This work has been supported by the US National Oceanic and Atmospheric Administration’s Office of Global Programs through cooperative agreement #NA87GP0061 on the Climate Assessment for the Southwest (CLIMAS), and by the US National Oceanic and Atmospheric Administration’s Paleoclimatology program, through grant #NA66GP0311 to Professor M.K. Hughes.


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2 December 2002