ISOTOPIC AND HYDROLOGICAL MODELING OF A CLOSED BASIN LAKE AND COMPARISON TO INSTRUMENTAL RECORDS OF DROUGHT, SCANLON LAKE, NORTH-CENTRAL WASHINGTON

Scanlon Lake is a small (<0.1 km2), closed-basin, alkaline lake located in the semi-arid rain shadow of the Cascade Mountains, a region prone to prolonged, severe drought. Due to its agricultural base, the regional economy relies heavily on water resources and therefore, is in need of a drought history that extends well beyond the instrumental record of the 20th century, a time frame too short to capture the full, historical range of drought frequency and magnitude. To this end, a continuous, lumped hydrological and isotopic model of the Scanlon lake watershed was built using local meteorological and soil data, detailed bathymetric surveys, and catchment topography analysis, and run in monthly time steps over the 20th century. The modeling results positively correlate to both recent (2005 – 2007) lake level and water isotope measurements and to a 20th century ostracod d18O record from a littoral zone sediment core obtained in 2005. Independent validation of the model results and of the ostracod d18O values as faithful recorders of drought is provided by their positive correlation to the regional instrumental PDSI record. Ongoing work involves extending the ostracod record to 2000 yrs BP, estimating pre-20th century local PDSI values based on the 20th century relationship between the model results and the d18O record from ostracods, and testing the model results through comparison to the regional, late Holocene tree-ring PDSI reconstruction of Cook et. al. (2004).

References:

Cook, E. R., Woodhouse, C. M., Eakin, C. M., Meko, D. M. & Stahle, D. W. (2004) Science 306, 1015–1018.