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Storms, Floods and Atmospheric Rivers in a Changing Climate

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Storms, Floods and Atmospheric Rivers in a Changing Climate Extreme (Hydroclimatic) Events in Western Mountains Michael Dettinger, USGS, SIO, La Jolla Geoff Schladow, UC Davis, TERC Marty Ralph, NOAA/ESRL/PSD Paul Neiman, Allen White, NOAA/ESRL/PSD Dan Cayan, USGS/SIO and others NOAA’s California-Nevada Applications Program Atmospheric Rivers Snowmelt Peaks (spring and summer) Front Range (fall and Upslopes winter) (Spring) Extreme Precipitation/Fl ooding Southwest Monsoon Mechanisms (summer & fall) Ralph et al., Obs Vision for Western States Water Council, 2011 Outline 1. What are atmospheric rivers? Why should we care? 2. Examples of AR impacts in the Tahoe basin 3. What changes can we anticipate in 21st Century storms & floods? Atmospheric Rivers Landfalling atmospheric rivers 3 Orographic cloud and precipitation 2 “Controlling layer” 1 (upslope winds) AltitudeMSL (km) Rain Atmospheric shadow River 0 Ocean -Lateral structure from satellite data (~400 km width & 2000 km long) -Vertical structure from airplanes & radar (intense jet of vapor transport between 1 – 2 km above sea level; 10-20 Mississippis) Last night’s atmospheric rivers Just how BIG are we talking about? Largest 3-day storm totals in >30 yrs COOP records Ralph & Dettinger, BAMS, 2012 Atmospheric rivers as resources & hazards • 87% of declared floods of Russian River CONTRIBUTIONS TO WATER YEAR since 1948 have been atmospheric rivers (ARs), (Ralph et TOTAL PRECIPITATION FROM ARs: al 2006; Florsheim & Dettinger, in review) (days 0 to +1), 1998-2008 • In Washington, 46 of 48 annual peak daily flows have been associated with ARs (Neiman et al 2011) • Responses of daily flows in American & Merced Rivers to ARs are typically order of magnitude larger than to other storms (Dettinger 2004, 2005) Dettinger et al. 2011 Arizona atmospheric-river storm, Jan 2010 Vertically integrated water vapor imagery (c) 20 Jan 2010 p.m. (d) 21 Jan 2010 p.m. AR #3 AR #3 (d) 00Z 22 Jan 2010 Total water vapor transports #3 Neiman et al., tentatively accepted, JHM Arizona atmospheric-river storm, Jan 21-23 2010 Neiman et al., tentatively accepted, JHM Southwest atmospheric-river storm, December 2010 Ralph & Dettinger, BAMS, 2012 Southwest atmospheric-river storm, December 2010 800% of normal Dec in Southern California (670 mm/26 in) Bountiful, UT, 12/24/2010 Flooding, Laguna Beach, 12/21/2010 Almost 400% of normal Dec in SE Utah (430 mm/17 in) Ralph & Dettinger, BAMS, 2012 Why ARs matter… Since 1950… •ARs as West Coast “drought busters” (33-74%)… • ARs & Mojave River aquifer recharge (57%)… • ARs & San Francisco Bay salinity variations (50-83%) • ARs & Sacramento Rvr floodplain inundation (78%) • ARs & Central Valley levee breaks (81%)… © Waters Why ARs matter… Atmospheric rivers, and the extreme events that they bring to the West, are particularly influential in many “environmental” contexts Thus, understanding, forecasting & projecting ARs is of direct importance to westerners Western systems—ecological, geomorphic, hydrologic, infrastructural, … --have all adapted in the context of ARs and their particular properties. Understanding that particular context and how we have modified it with structures etc should help us to better manage & restore elements & services in this new world we’ve created. © Waters Lake Tahoe: Storms, inflows, sediment loading & clarity Area: 500 km**2 Altitude: 1897 m asl Residence time: 650 yr Lake Tahoe: ARs as big warm storms On average, AR storms at Tahoe are warmer by 2ºC and wetter by 85% than wet days in general. Lake Tahoe: Warm storms & ARs Of 38 days with Tmin > 0ºC & Precipitation > 5 cm at Tahoe City, WY1948-2010 81% AR Not AR All such days AR days among them Lake Tahoe: Lake Level Jumps & ARs 76 days when Lake level rises by > 5 cm/day since 1958 84% ARs AR storm Not Ar 700 mb Vapor Transport Rates, 15 largest 1-day lake increases Lake Tahoe sediment loading Upper Truckee River at South Lake Total sediment transports by high-load days vs other days, 1971-92 36 High load days Daily Suspended Sediment Loads from Upper Truckee River All other days Upper Truckee River at South Lake Total suspended sediments transported to lake Number of days 0.5% 18% Low-load days High-load days High-load days Flow Contributions to Lake 4% Other flows High-load flows The total amount (18% of all transport) of suspended sediments transported to the Lake by the Upper Truckee on the days with loads > 150 tons/day is out of proportion to the flows on those days (4% of all flows) & far out of proportion to the number of such days (0.5% of days). Sediment transport & warm storms In WY1981-1992, there were 9 days with > 5 cm of precipitation & Tmin > 0C occurred at Tahoe City. Total sediments transported 6% of total Warm rain sed loads Rest of loads Numbers of days Warm rains Rest of days On average, those 9 warm rain days yielded 242 tons/day of suspended sediments, whereas the 12-yr average daily sediment loads were 8 tons/day…30 times as much. Lake Tahoe: ARs & sediment loading Upper Truckee River at South Lake Total sediment transports by 36 high-load vs other days, and by AR high-load vs other high-load days 12% 6% Other days Daily Suspended Sediment Loads High-load AR days from Upper Truckee River Other high-load days Numbers of days in each category Lake Tahoe clarity TERC, person. comm., 2012 Anomalous 500 mbar Levels Anomalous 700 mbar Temperatures Composites of atmospheric conditions on the 5 days preceding each of 10 days with largest anomalous secchi depths, 1967- 2012 Anomalous Integrated Water Vapor Transports Anomalous depths are secchi- depths minus 4th order long- term trend and 5th order seasonal cycle Sudden changes in Lake Tahoe clarity Largest Measurement-to-Measurement Changes in Lake Clarity, WY1968-2011 (>10 m!) Of 15 occasions with largest msmt-msmt CLARITY INCREASES, ALL 15 were preceded by stormy conditions, and… 11/15 were preceded by ARs. 73% ARs Of 15 occasions with largest msmt-msmt CLARITY DECREASES, ALL 15 were preceded by high pressures, as offshore blocking patterns or overhead. Lake Tahoe: AR storms & clarity However, on the longer (seasonal-annual) scales, more ARs are associated with annual CLARITY DECLINES Lake Tahoe: AR storms & clarity r = 0.55 Lake Tahoe: AR storms & clarity Trend/yr Secchi Depths from UC Davis TERC & AR/PE Counts from Dettinger et al., Water, 2011 Future of Western storms & floods? Atmospheric Rivers Snowmelt Peaks (fall and (spring and summer) ARs ? winter) Snowmelt ? Monsoons ? Extreme Precipitation/ Southwest Flooding Monsoon (summer & Mechanisms fall) Atmospheric Rivers & Climate Change Observed Projected Water Vapor & By end of 21st Century, most GCMs (in a Low-Level Winds 7-member A2-emissions ensemble) yield: • More atmospheric vapor content, but weakening westerly winds Net increase in “intensity” of extreme AR storms Projected Water Vapor & • Warmer ARs (+1.8 C) snowline raised Low-Level Winds by about 1000 feet on average • Lengthening of AR seasons (maybe?) Dettinger, JAWRA, 2011 Atmospheric Rivers & Climate Change 2046-2065 Intensities of ARs from different directions 1961-2000 San Jacinto Mtns San Gabriel Mtns Santa Ana Mtns 2081-2100 Dettinger, JAWRA, 2011 Snow Mediated Floods & Climate Change Observed (1949-2003) Observed (past 85 yrs) Trends in Annual-Peak Flows Hirsch & Ryberg, HSJ, 2011 McCabe et al., BAMS, 2006 Snow Mediated Floods & Climate Change Projected (1951-2099) Rainfall runoff 1951-99 • Wintertime flood flows increase in frequency & Snowmelt magnitude 2001-49 • Spring- snowmelt high flows decline 2051-99 CalDWR media slide Das et al., 2011, Climatic Change Projected Floods in Sierra Nevada 16 GCMs, A2 emissions Northern Sierra Nevada Southern Sierra Nevada Change in mean Change in mean Drier avg annual flow annual flow Change in flood flows with various return periods 2001-49 2051-99 Return period Das et al., in prep Monsoon storms/floods? Vapor Transports are a missing link! Conclusions • Understanding atmospheric rivers will be crucial for addressing floods, water resources & a variety of environmental processes around the Western US • Forecasting ARs is basic to forecasting/managing key environmental processes • The ability to follow vapor as it is carried, aloft, into the West (by ARs or monsoons) is a critical gap in our ability to track, diagnose and predict important storms and floods. • Although the science is still nascent, more intense storms, higher snowlines, and resulting greater flood risks are being projected for the 21st Century. http://www.esrl.noaa.gov/psd/atmrivers/ • Dettinger, M.D., 2005, A long-term (50 yr) historical perspective on flood-generating winter storms in the American River basin: Proc. 2005 California Extreme Precipitation Symposium, 62-73. • Dettinger, M.D., 2011, Climate change, atmospheric rivers and floods in California—A multimodel analysis of storm frequency and magnitude changes: Journal of American Water Resources Association, 47, 514-523. • Dettinger, M.D., Ralph, F.M., et al.., 2012, Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California: Natural Hazards, 60, 1085-1111. • Das, T., Dettinger, M., Cayan, D., and Hidalgo, H., 2011, Potential increase in floods in California’s Sierra Nevada under future climate projections: Climatic Change, 109, 71-94. • Florsheim, J., and Dettinger, M., in review, Intentional levee breaks promote lowland floodplain biogeomorphic processes: as chapter in Hudson, P., and Middelkoop, H. (eds.), Geomorphology and management of embanked floodplains—North American and European fluvial systems in an era of global environmental change, Springer-Verlag, 15 p. • McCabe GJ, Clark MP, Hay LE (2007) Rain-on-snow events in the Western United States. BAMS, 1–10 • Neiman, P.J., Ralph, F.M., Moore, B.J., Hughes, M., Mahoney, K.M., and Dettinger, M.D., in revision, The landfall and inland penetration of a flood-producing atmospheric river in Arizona—Part I, Observed synoptic-scale and hydrometeorological characteristics: J.
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