The coming megafloods

Climate, Atmospheric Sciences and Physical Oceanography Division, Scripps Institution of Oceanography, La Jolla, Calif., USA.
Scientific American (Impact Factor: 1.07). 01/2013; 308(1):64-71. DOI: 10.1038/scientificamerican0113-64
Source: PubMed
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    • "Recent satellite observations have linked severe flooding in California with AR or low level jets on the frontal edge of winter cyclones that draw moisture and warm air from the tropics (near Hawaii) to the west coast of North America (Ralph et al., 2004; Neiman et al., 2008). Extrapolating from the observation that 1861e62 flood (gray layer) was generated by an AR, every preceding gray layer in the SBB sequence is assumed to be associated with one (Dettinger and Ingram, 2013). As anticipated given aforementioned observations, the most prominent peaks in PC1 values coincide with El Ni~ no events (i.e. "
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    ABSTRACT: The Mediterranean climate of southern California is marked by droughts and extreme precipitation events. Here we use elemental variations generated by scanning X-ray fluorescence (XRF) to identify droughts and floods in recently deposited (1755–2008) sediments of Santa Barbara Basin (SBB) from box core SPR0901-04BC. The first principal component (PC1) of the scanning XRF elements has high loadings for elements associated with the lithogenic component of SBB laminae couplets, while the second (PC2) is associated with biogenic components. We interpret PC1 as a proxy for river runoff and PC2 as a proxy for marine productivity. High values of PC1 are associated with El Niño events and positive (warm) phases of the Pacific Decadal Oscillation (PDO), while low values of PC2 are associated with El Niño events and negative (cool) phases of the PDO. Droughts such as the 1934–40, 1949–56, and 1989–91 events coincide with low PC1 values. In addition to distinguishing interannual and decadal variability in the elemental composition of SBB sediments, several historic floods can be recognized including a gray flood layer associated with the 1861–62 flood, and a peak in PC1 associated with the flood following the St. Francis Dam disaster in 1928.
    Quaternary International 02/2015; DOI:10.1016/j.quaint.2015.01.026 · 2.06 Impact Factor
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    • "). 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). "
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    ABSTRACT: Channel incision occurs in the “Anthropocene,” where natural river processes and climate variation increasingly interact with human activity. Causes of “Anthropocene” incision include landuses that change the ratio of discharge to sediment load, lower baselevels, or human activities that otherwise alter fluvial systems, such as channelization. This paper reports a field study of an alluvial channel incised into valley fill within the northern Coast Ranges of California. At this site, channel slope adjustments associated with incision, indicated by bank heights of ∼5–8 m, increased transport capacity and excess shear stress by over 20%. The incision exposed Holocene valley fill in eroding channel banks. Results of field surveys enabled development of a dimensionless metric “relative incision,” ht/de, that quantifies the ratio of terrace height (ht) relative to effective flow depth (de). The ratio is predicted to be near a threshold value of 1.0 in stable alluvial channels; in incised alluvial channels the ratio is predicted to exceed 1.0. Further application and testing will provide information to aide in managing incised systems where complex feedbacks in coupled human–landscape systems may promote or dampen incision.
    Anthropocene 10/2013; 2. DOI:10.1016/j.ancene.2013.10.006
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    • "Flows from the Sierra Nevada provide about one-third of the water supplies serving about 25 million people across the entire length of the State and irrigation supplies for at least $36 billion/year in agriculture (Service, 2007; USDA, 2011). However, in addition to being the largest water supply source for the State, rivers from the Sierra Nevada have also, throughout history and prehistory, been the sources for devastating floods in the Central Valley (Dettinger and Ingram, 2013). The management of flows from the range have always been challenged by the tension between their value as water supplies and the risks they pose as major flood generators, a tension that may be greatly aggravated if flood risks increase with the changing climate. "
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    ABSTRACT: Downscaled and hydrologically modeled projections from an ensemble of 16 Global Climate Models suggest that flooding may become more intense on the western slopes of the Sierra Nevada mountains, the primary source for California's managed water system. By the end of the 21st century, all 16 climate projections for the high greenhouse-gas emission SRES A2 scenario yield larger floods with return periods ranging 2-50 years for both the Northern Sierra Nevada and Southern Sierra Nevada, regardless of the direction of change in mean precipitation. By end of century, discharges from the Northern Sierra Nevada with 50-year return periods increase by 30-90% depending on climate model, compared to historical values. Corresponding flood flows from the Southern Sierra increase by 50-100%. The increases in simulated 50 year flood flows are larger (at 95% confidence level) than would be expected due to natural variability by as early as 2035 for the SRES A2 scenario.
    Journal of Hydrology 08/2013; 501:101-110. DOI:10.1016/j.jhydrol.2013.07.042 · 3.05 Impact Factor
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