Young, Charles A., Marisa I. Escobar‐Arias, Martha Fernandes, Brian Joyce, Michael Kiparsky, Jeffrey F. Mount, Vishal K. Mehta, David Purkey, Joshua H. Viers, and David Yates, 2009. Modeling the Hydrology of Climate Change in California’s Sierra Nevada for Subwatershed Scale Adaptation. Journal of the American Water Resources Association (JAWRA) 45(6):1409‐1423.
Abstract: The rainfall‐runoff model presented in this study represents the hydrology of 15 major watersheds of the Sierra Nevada in California as the backbone of a planning tool for water resources analysis including climate change studies. Our model implementation documents potential changes in hydrologic metrics such as snowpack and the initiation of snowmelt at a finer resolution than previous studies, in accordance with the needs of watershed‐level planning decisions. Calibration was performed with a sequence of steps focusing sequentially on parameters of land cover, snow accumulation and melt, and water capacity and hydraulic conductivity of soil horizons. An assessment of the calibrated streamflows using goodness of fit statistics indicate that the model robustly represents major features of weekly average flows of the historical 1980‐2001 time series. Runs of the model for climate warming scenarios with fixed increases of 2°C, 4°C, and 6°C for the spatial domain were used to analyze changes in snow accumulation and runoff timing. The results indicated a reduction in snowmelt volume that was largest in the 1,750‐2,750 m elevation range. In addition, the runoff center of mass shifted to earlier dates and this shift was non‐uniformly distributed throughout the Sierra Nevada. Because the hydrologic model presented here is nested within a water resources planning system, future research can focus on the management and adaptation of the water resources system in the context of climate change.
The functional flows model integrates hydrogeomorphic processes and ecological functions for stream physical habitat evaluations. Functional flows are discharge values that serve ecological uses. Assessments of functional flows are based on evaluation of shear stress dynamics. The analysis is based on the occurrence of sediment transport regimes defined by threshold values of Shields stress estimated from discharge (Q), a parameter ( f) governing depth response to incremental discharge changes, water surface slope (S) and media grain size (D 50 ). As an example, the model was tuned for fall-run Chinook salmon spawning. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)-both reliant on shear stress dynamics. A numerical experiment and sensitivity analysis using a wide range of realistic values of input variables indicated the effect of each variable on flow functionality.
20This study applies the functional flows model that integrates hydrogeomorphic processes and 21 ecological functions to assess physical habitat. Functional flows are discharge values that serve 22 ecological uses. The model was adjusted to evaluate gravel-bed riffle functionality for fall-run 23 2 Chinook salmon with respect to river rehabilitation on the Mokelumne River and flood-induced 1 channel change on the Yuba River. The goal was to test if differences in ecological performance 2 were traceable to differences in hydrogeomorphic conditions. Ecological functions studied were 3 bed occupation (spawning, incubation, and emergence) and bed preparation (river bed reworking 4 periods)-both reliant on shear stress dynamics. Model outputs included number of days that have 5 functional flows, ranges of functional flows that provide favorable sediment transport stages, and 6 the efficiency of a site to produce functional flows. Statistical significance of results was tested 7 using non-parametric tests.
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