, 2006); thus, we infer that high magnitude, short

duration atmospheric river storms are similarly likely to govern flood hydrology in the ungaged Robinson Creek basin. Average annual rainfall recorded at the Boonville HMS gage (data from Western Regional Climate Center) near the mouth of Robinson Creek in Boonville, CA, over a 58 year period between water year 1937 and 1998 shows variability, with an average rainfall of 1016 mm/yr (Fig. 2). Annual rainfall totals measured at Yorkville, approximately 20 km east of Boonville, since 1898 provide a 115-year proxy record for estimating timing of storms, and further demonstrate variability characteristic of the region. Proxy data from other watersheds in northern California suggest that the period prior to the instrumental CDK assay record included extreme storms, such as occurred in 1861–1862 throughout California—and would have influenced the early Euro-American settlers in Anderson Valley. Storms with equal or greater magnitude occurred in AD 1600 and between 1750 and 1770, with a recurrence check details interval over the past 800 years of ∼100–120 years (Ingram and Malamud-Roam, 2013). Still larger storms in California are thought to have recurrence intervals on the order of 200 years (Dettinger and Ingram,

2013). Other work suggests that moderate floods in northern California capable of geomorphic change recurred during ∼25% of years over the past 155 years (Florsheim and Dettinger, 2007). Niclosamide Together, these records suggest that extreme floods, as well as more moderate storms and droughts are characteristic of natural climate variability over multiple centuries including the historical period. Moreover, recent work suggests that since 1850, California’s climate

has been relatively stable and benign compared to variations typical of the past 2000 years or more (Malamud-Roam et al., 2006; 2007). Thus, even a century long rainfall record such as exists at Yorkville must be considered within the context of longer-term climate variation. The pre-incision Robinson Creek channel-floodplain environment supported riparian trees at an elevation such that frequent inundation was likely. Storms that generate enough runoff to initiate overbank flow in alluvial channel-floodplain systems were fundamental in creating this environment. Channel-floodplain hydrologic connectivity is still functioning in downstream portions of the Navarro River (e.g. overbank flow occurred during water years 1956, 1965, 1973, 1983, 1986, 1996, 1997, 1986, 1983, 1995, 1998; Florsheim, 2004). However, in Robinson Creek in Boonville, the 1986 and later floods remained within the channel, and although local residents recall high water during earlier floods during water years 1956, 1965, and 1983—their oral histories do not recount overbank flow (Navarro River Resource Center, 2006).