Options for Steelhead Recovery in an Uncertain Future Climate: A Case Study of the Pajaro River, California

Biologists commonly assume that restoration or partial-restoration of natural processes to river systems will increase the resilience of fish populations to climate change. We describe a modeling study that examines this assumption for steelhead (Oncorhynchus mykiss) during a specific phase of its life-cycle (upstream migration) in a particular river system (the Pajaro River of California). Flood-plain conservation in the upper basin and conversion of levees to setback levees in the lower basin has been proposed for purposes of flood-management. Using standard rainfall-runoff modeling (HEC-HMS, HEC-RAS), and a simple model of steelhead migration energetics, we examine how these two management options interact with various climate scenarios to provide or preclude migration opportunities in the Pajaro basin of the future. A key issue is how future changes in annual precipitation manifest as changes in intensity, duration, and number of storms per year.