Alison Anders, Assistant Professor

Stable isotopes of hydrogen and oxygen in water provide insight into

precipitation processes and hydrology.  They are also increasingly being used to infer elevation changes in mountain ranges over geologic time. A new technique for mapping spatial variability in climatological precipitation using the stable isotopic composition of surface water is tested in the Olympic Mountains of Washington State.  A linear orographic precipitation model extended to include in effects of isotopic fractionation via Rayleigh distillation predicts precipitation patterns and isotopic composition of surface water given seven parameters relating to the climate and isotopic composition of source water.  A constrained random search of the seven-dimensional parameter space is used to determine the best-fitting parameter set and define confidence intervals on parameter values and precipitation patterns. An independent high-resolution precipitation climatology for the Olympics documents precipitation gradients similar in shape and magnitude to the model derived from surface water isotopic composition.  These results suggest that stable isotopes could be used to map long-term precipitation patterns in other mountain ranges and provides a context for interpretation of geologic records of water stable isotopes as a function of topographic change.