Application of Streamflow Reconstruction to Water Resources Management - Dendroclimatology - page 255

particularly in the Pacific Northwest (Mote et al. 2005 ) . The decline is mostly
attributed to warming winter temperatures, even with periodic and regional increases
in precipitation (Mote et al. 2005 ) . Effects of this reduction of snowpack on hydrol-
ogy include earlier runoff dates and changes in the distribution of runoff over
the course of the water year, with more runoff earlier in the water year (Stewart
et al. 2004 ) . These changes could result in greater losses due to evaporation and an
overall reduction in water year flows, if not compensated for elsewhere in the hydro-
logic cycle. Future climate projections suggest large-scale warming on the order of
1 2 ◦ C across the western United States over the next half century (Barnett et al.

2004 ) .
These trends and projections bring up the question, is the record of past hydro-
climatic variability an appropriate analog to future conditions? In some respects,
the climate of the future will be unlike the climate of the past; however, natural
hydroclimatic variability is likely to continue, superimposed on changes in climate
due to anthropogenic activities. An understanding of natural hydroclimatic vari-
ability on decadal and longer timescales can be obtained only from centuries-long
reconstructed records, and is critical for understanding the large-scale, slowly vary-
ing oceanic/atmospheric drivers of climate. These large-scale controls are likely
to continue to operate in the future, and a baseline knowledge of the role of
oceanic/atmospheric conditions in long-term regional hydroclimatic variability is
necessary to understand how the climate system operates now and how it will under
warmer conditions. The challenge will be to blend the knowledge gleaned from
the past with projections for climate under climate change scenarios to get a bet-
ter indication of the range of hydroclimatic conditions and events to expect in the
future.

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8.5 Conclusion

A.E. Douglass, in the foreword to Edmund Schulman's ( 1945a ) landmark report on
tree-ring hydrology of the Colorado River basin, wrote that he believes Schulman
'offers something of novel importance and value to the hydrologists of the West,'
and that the report will 'carry over to the managers of hydroelectric and reclamation
projects about the world a good idea of the type of information that may be secured
from properly selected and analysed [sic] trees.' Some 50 years later, we see that
much has been accomplished but that the potential of tree-ring analysis in hydrol-
ogy has only begun to be tapped. Early studies were most intensive in the western
United States, with groundwork for quantitative streamflow reconstructions laid by
H.C. Fritts and C.W. Stockton. The geographic scope has expanded with the growth
of dendrochronology as a science, the development of tree-ring laboratories in var-
ious countries, and the spatial extension of tree-ring networks. The contributions
of dendrohydrology continue at an accelerating pace as human demands on lim-
ited water resources increase and the need for efficient long-term planning in water