Tree‐ring Reconstruction of Upper Gila Rwer Discharge1

ABSTRACT: Effective planning for use of water resources requires accurate information on hydrologic variability induced by climatic fluctuations. Tree‐ring analysis is one method of extending our knowledge of hydrologic variability beyond the relatively short period covered by gaged streamflow records. In this paper, a network of recently developed tree‐ring chronologies is used to reconstruct annual river discharge in the upper Gila River drainage in southeastern Arizona and southwestern Arizona since A.D. 1663. The need for data on hydrologic variability for this semi‐arid basin is accentuated because water supply is inadequate to meet current demand. A reconstruction based on multiple linear regression ( R 2 =0.66 ) indicates that 20th century is unusual for clustering of high‐discharge years (early 1900s), severity of multiyear drought (1950s), and amplification of low‐frequency discharge variations. Periods of low discharge recur at irregular intervals averaging about 20 years. Comparison with other tree‐ring reconstructions shows that these low‐flow periods are synchronous from the Gila Basin to the southern part of the Upper Colorado River Basin.