Over the last half century, the Foothill Yellow-legged Frog (R. boylii) has declined dramatically, especially in Southern California and the southern Sierra Nevada mountains.

In this project, we seek to improve our understanding of the impacts of varying spring flow regimes on stream ecology, through empirical field studies, and water management, through hydropower optimization modeling.

This study compares commonly used methods of defining habitat suitability criteria and applying those to instream flow models for R. boylii in the Sierra Nevada of California. First, regional habitat suitability criteria (HSC) are developed using standard univariate and multivariate techniques, and the predictive performance and transferability of different HSC methods are evaluated. Second, three of the most commonly used instream flow assessment techniques are evaluated: (1) one-dimensional habitat modeling, (2) two-dimensional hydrodynamic modeling, and (3) expert habitat mapping (judgement-based mapping by species experts). A comparison table is provided to aid resource managers in selecting the most appropriate habitat assessment method for R. boylii given the specific conditions of a hydropower relicensing project.