Runoff variability in the Truckee-Carson River basin from tree rings and a water balance model

Abstract

Regional warming and associated changes in hydrologic systems pose challenges to water supply management in river basins of the western United States, and call for improved understanding of the spatial and temporal variability of runoff. We apply a network of total-width, subannual width and delta blue intensity tree-ring chronologies in combination with a monthly water balance model to identify droughts and their associated precipitation (P) and temperature (T) footprints in the Truckee-Carson River basin (TCRB). Stepwise regression gave reasonably accurate reconstructions, from 1688 to 1999, of seasonal P and T (e.g., R2 = 0.50 for May-Sept T). These were disaggregated to monthly values, which were then routed through a water balance model to generate “indirectly” reconstructed runoff. Reconstructed and observed annual runoff correlate highly (r = 0.80) from 1906 to 1999. The extended runoff record shows that 20th century droughts are unmatched in severity in a 300-year context. Our water balance modeling reconstruction advances the conventional regression-based dendrochronological methods as it allows for multiple hydrologic components (evapotranspiration, snowmelt, etc.) to be evaluated. We found that imposed warming (3 °C and 6 °C) generally exacerbated the runoff deficits in past droughts but that the impact could be lessened and sometimes even reversed in some years by compensating factors, including changes in snow regime. Our results underscore the value of combining multi-proxy tree-ring data with water balance modelling to place past hydrologic droughts in the context of climate change.