Time-Varying Sensitivity Analysis and its Relationship to Shifting Annual Conditions in California Watersheds

Changing climate affects watershed hydrologic cycles, therefore it is becoming increasingly important to analyze outcomes of this variability on long-term watershed behavior. To examine this, we applied time-varying sensitivity analysis to twelve watersheds located in various sites across California. In particular, we aim to analyze how strong seasonal and annual shifts from wet to dry may be attributed to shifting importance of different model parameters and therefore key watershed processes. We focus on this region in particular because of its climate and tendency for extreme weather events, which allows us to better analyze the effects of changing climate on watershed controls. Hydrology was simulated using a simple lumped rainfall-runoff model (Hymod) over a 36-year period (1981-2015). Sensitivity analysis revealed that watersheds at different elevations experienced differential importance of baseflow contributions. Moreover, yearly parameter importance applied to hydrologic signatures compared across 36 years showed varying parameter sensitivity from year to year in addition to a few abnormal annual responses in years with extreme floods and extreme droughts. This work reveals different watershed responses to changing climate conditions and provides important information that can be additionally tested with data driven approaches to helps us better understand hydrologic controls in watersheds with strong seasonal and annual shifts in behavior.