Paleo Slide Set: Tree Rings: Ancient Chronicles of Environmental Change
Observed & reconstructed number of precipitation days in winter, northern Arizona & New Mexico.

A tree-ring chronology built from old, sensitive trees will reveal the common climate 
signal found in the trees throughout an area. The chronology, usually in the form of 
a time series of ring width or density indices, is calibrated with a climate record 
for the period of time common to both climate records and the chronology. The character 
of the relationship between climate and tree growth is assessed and a statistical model 
is derived to describe that relationship. In this figure, the total number of precipitation 
days in winter for a region in northern Arizona and New Mexico was reconstructed from 
a set of tree-ring chronologies in the southwestern United States. The purple line shows 
the observed record of numbers of precipitation days while the green line shows the values 
reconstructed from the chronologies. The match, although not perfect, is very close, 
and reflects both high and low frequency variations in precipitation days in this region 
for centuries prior to the availability of instrumental observation.

Photo Credits:
Connie Woodhouse
NOAA Paleoclimatology Program