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North America--Northern Cascades

Drought History of the Pacific NW from Lake Sediment Records

Recent droughts affecting the American West are among the most severe on record (e.g. Cook et al., 2004). This aridity, combined with rapid population growth, limited water resources, receding glaciers and decreased mountain snow pack provides the impetus to improve our understanding of how and why the hydrologic cycle has varied in the past. The goal of this project is to produce quantitative estimates of the frequency, duration and strength of droughts in the Pacific NW for the Holocene using stable isotope analyses on lacustrine carbonates combined with modeling studies grounded with instrumental data.

Over 60 years of historic airphotographs help ground truth the timing and magnitude of 20th century lake-level changes.

Left - Stable isotope measurements on surface waters from lakes and rivers in the Pacific NW show that open basin lakes and rivers plot along the Global Meteoric Water Line (GMWL) while samples from closed basin lakes show evaporative enrichment of the heavy isotopes and plot on a trajectory off of the GMWL on the Regional Evaporation Line (REL). Right - Samples from two lakes show evaporative enrichment of the heavy isotopes during the dryer conditions starting in 1999.

Comparison of Scanlon and Castor lake d18O records with modeling results and the instrumental record demonstrates that the sediments faithfully register changes in P-E. All x-axes are scaled to show increasing aridity to the right. (A) Scanlon Lake d18O record (blue) and the stable isotope mass balance modeling results (red) which track the local PDSI shown in (C). (B) Castor Lake d18O record (blue) and the stable isotope mass balance modeling results (red). (C) Instrumental Palmer Drought Severity Index (PDSI) from the closest metrological station - used in our models (D). Instrumental PDSI from grid point 43 with a 20-yr low-pass filter (Cook et al., 2004). (E) Instrumental record of the Pacific Decadal Oscillation (PDO) Index with 20-yr low-pass filter.

Reference: Cook, E. R., Woodhouse, C. A., Eakin, C. M., Meko, D. M. and Stahle, D. W. (2004). Long-term aridity changes in the western United States. Science 306, 1015-1018.

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Revised Dec 2005

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