Jay Lund and colleagues have modeled a range of possible impacts of climate change on flood flows in California. From a nice summary on the UC Davis California WaterBlog:
Warming generally worsened flood inflows into reservoirs. Even with less precipitation, warmer conditions often increased flood inflows to reservoirs. When more precipitation fell as rain, rather than snow, and more existing snowpack melted, flood volumes increased. This was particularly true for historical storms that were “cold”, where much of the precipitation was held as snowpack. Warm storms, which historically produced less snow, were less affected by warming.
But the research suggests adaptations in reservoir operating rules can be relatively effective in dealing with the problem:
Reservoirs with flood operating rules that respond to the wetness of their watersheds seemed to adapt well to changes in climate, even fairly severe changes in temperature and precipitation. This was true for Shasta and Oroville Reservoirs, whose existing flood operation rules vary with moisture conditions upstream. This shows that existing reservoirs may have considerable ability to accommodate flooding effects of climate warming.