A water balance approach for reconstructing streamflow using tree-ring proxy records.

Summary Tree-ring data have been used to augment limited instrumental records of climate and provide a longer view of past variability, thus improving assessments of future scenarios. For streamflow reconstructions, traditional regression-based approaches cannot examine factors that may alter streamflow independently of climate, such as changes in land use or land cover. In this study, seasonal water balance models were used as a mechanistic approach to reconstruct streamflow with proxy inputs of precipitation and air temperature. We examined a Thornthwaite water balance model modified to have seasonal components and a simple water balance model with a snow component. These two models were calibrated with a shuffled complex evolution approach using PRISM and proxy seasonal temperature and precipitation to reconstruct streamflow for the upper reaches of the West Walker River basin at Coleville, CA. Overall, the modified Thornthwaite model performed best during calibration, with R 2 values of 0.96 and 0.80 using PRISM and proxy inputs, respectively. The modified Thornthwaite model was then used to reconstruct streamflow during AD 1500–1980 for the West Walker River basin. The reconstruction included similar wet and dry episodes as other regression-based records for the Great Basin, and provided estimates of actual evapotranspiration and of April 1 snow water equivalence. Given its limited input requirements, this approach is suitable in areas where sparse instrumental data are available to improve proxy-based streamflow reconstructions and to explore non-climatic reasons for streamflow variability during the reconstruction period. [ABSTRACT FROM AUTHOR]