*Article* **California Drought Outlooks Based on Climate Change Models' Effects on Water Availability**

**Lauren Lynam and Thomas Piechota \***

Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA; laurenmlynam@gmail.com

**\*** Correspondence: piechota@chapman.edu

**Abstract:** Future streamflow in California is evaluated based on eight climate projections models and the effects on water availability. The unimpaired projected streamflow for eleven California rivers, collected from Cal-Adapt, are compared with unimpaired historical flows (1950–2015) using eight climate model projections (2020–2099) identified as representative as possible future scenarios; Warm Dry RCP 4.5, Average RCP 4.5, Cool Wet RCP 4.5, Other RCP 4.5, Warm Dry RCP 8.5, Average RCP 8.5, Cool Wet RCP 8.5, and Other RCP 8.5. Projected drought deficits (or magnitudes), durations, and intensities are statistically tested against historical values to determine significance of differences between past streamflow and future streamflow. The models show significant differences between historical and projected streamflow with all three drought categories (deficit, duration, intensity), using difference in means *t*-tests. Warm Dry and Other simulations are projected to have larger droughts (2–3 times larger) than the historical record. Average and Cool Wet simulations are projected to have fewer droughts than the historical period. Results are consistent for 4.5 and 8.5 RCP scenarios that represent two different greenhouse gas emission levels. Potential impacts of such streamflow variations are discussed.

**Keywords:** drought; climate; water; hydrology; streamflow
