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Tree-ring Reconstructions of Past Climate in the Southwest
The longest instrumental records date back about 100 years at some locations in the Southwest. While these records are crucial to understanding variations in precipitation over the last 100 years, the full range of variability in southwestern climate may not have been experienced within this time frame. The extension of the record to earlier times can provide additional information on the length and severity of past droughts and can be used to provide water managers with information about the range of pre-industrial climate variability.
Tree rings provide a useful tool to help extend winter precipitation records further back in time. The growth of many Southwestern tree species can be linked directly to the total amount of precipitation that falls during the cool season, or winter between November—April. Statistical models have been developed to relate tree growth to precipitation. These relationships are then applied to periods prior to the instrumental record to reconstruct past precipitation back a thousand years.
This research used tree-growth information collected from hundreds on trees growing at 19 sites to reconstruct total cool-season precipitation (November—April) back to AD 1000 using linear regression and a neural network reconstruction methods (see Methods for more details). Individual reconstructions were developed for each of the National Climatic Data Center climate divisions in Arizona and New Mexico.