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Floods of 2010: Examining Observed and Future Impacts of Increased Rainfall and Flooding
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Floods of 2010: Examining Observed and Future Impacts of Increased Rainfall and Flooding

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Presentation by Dave Vallee, Hydrologist in charge, National Weather Service.

Presentation by Dave Vallee, Hydrologist in charge, National Weather Service.

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  • 1. The Floods of March 2010Examining Observed and Future Impacts of Increased Rainfall and Flooding
    David R. ValleeHydrologist-in-ChargeNWS/Northeast River Forecast Centerhttp://weather.gov/nerfc
    Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10
  • 2. The NOAA Hurricane Outlook for the Atlantic Basin!
    But first: A Public Service Announcement!
    Hurricane Bob – Landfall 8/19/1991
    Bonnet Shores after Carol - 8/31/1954
  • 3. What is forecast for the 2011 Season?
    ACE Index Estimate
    Conditions Setup
    Named Storms: 12-18Hurricanes: 6-10Major Hurricanes: 3-6 (Cat 3, 4 or 5)
  • 4. Active Season = Greater Threat?
    Consider the following regarding hurricanes which
    made landfall on the coast of southern New England:
    1938 Season storm total = 8 (Cat 3)
    1944 Season storm total = 11 (Cat 3)
    Carol/Edna ‘54 Season storm total = 10 (2 Cat 3’s)
    Donna/1960 Season storm total = 7 (Cat 2)
    Gloria 1985 Season storm total = 11 (Cat 2)
    Bob 1991 Season storm total = 8 (Cat 2)
  • 5. The theme of the prevailing summer weather pattern ultimately determines our vulnerability
    Point at which New Englanders needs to take action!
  • 6. The Floods of March 2010Examining Observed and Future Impacts of Increased Rainfall and Flooding
    Outline
    * A bit about the Northeast River Forecast Center
    * What ingredients brought us to such a remarkable flood event in March 2010?
    * Historical Perspective
    * What does this all mean in light of climate change?
    Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10
  • 7. River Forecast Center Responsibilities
    Calibrate and implement a variety of hydrologic and hydraulic models to provide:
    River flow and stage forecasts at 180 locations
    Guidance on the rainfall needed to produce Flash Flooding
    Ensemble streamflow predictions
    Ice Jam and Dam Break support
    Water Supply forecasts
    Partner with NOAA Line Offices to address issues relating to Hazard Resiliency, Water Resource Services, Ecosystem Health and Management, and Climate Change
    Moderate flooding - Connecticut River at Portland, CT.
  • 8. http://www.weather.gov/nerfc
    Click on “Self Brief Page”
    NERFC Hydromet Self-briefing Page
  • 9. So what brought us to the tipping point during the last week of March 2010?
    It was not caused by
    One single Nor’easter or one Coastal Storm
    Snowmelt
    Improper water management
  • 10. So what brought us to the tipping point?
    It was caused by:
    The atmospheric river – “energized” by El Nino
    Blocking high pressure over Greenland
    A sequence of heavy rainfall events over 5 weeks
    Record monthly rainfall totaling 12-18 inches
    Axis of each event over Pawcatuck & Pawtuxet Valleys
    Saturated ground
    A “chuck-full” Scituate Reservoir
    Designed for Water Supply not Flood Control!
    Swollen streams and ponds running well above normal
    The lack of nature’s grasses, flowers and trees
    Pre-growing season – no Evapo-transpiration to help us out
  • 11. Major to Record flooding across southeast New England
  • 12. The Blackstone ResponseDodged a huge bullet – as heaviest rains stayed south of the basin Considerable flooding on mainstem and many small streams
  • 13. The Pawtuxet’s Record Response
    Dramatic “urban response” in the lower basin followed by record reservoir flows from Scituate Reservoir
  • 14. Pawcatuck Basin – similar responses
    Pawcatuck River – Wood River Junction
    Pawcatuck River – Westerly, RI
  • 15. Historical Footnotes
    Extremely rare to set two record flood elevations in two weeks – as was done on the Pawtuxet
    Consider this fact:
    The storms in March 2010 dumped over 16 inches of rain
    The record Flood for the Blackstone in 1955 was the result of over 10 inches in ONE DAY with over 14 to 16 inches of rain in 1 week in Woonsocket northward through the head waters in Worcester.
    Fits pattern of more intense heavy rainfall events which have been impacting the Northeast since the mid 1990s.
    Merrimack Oct’96, Hurricane Floyd flooding Sept ‘99, Connecticut, Merrimack, Blackstone Oct’05, Mother’s Day 2006 Merrimack valley, May 2007, and now March 2010
    An accumulation of “change”
  • 16. The Basin itself…many twists/turns and tremendous urbanization of the lower watershed post 1968 – which corresponds to the jump in flood frequencies
    Natic Dam
    Royal Mill Dam
    Arctic Dam
  • 17. Pawtuxet River Flood Frequency
    Post Mall and I-95 construction
  • 18. Blackstone River Flood History
    Post USACE Flood Control Product Construction
  • 19. Rhode Island Temperature Trend
    Annual TemperatureProvidence, RI 1933-2010
    *
    Trend line: y=1/61x +18.65
    *
    Prediction for 2020= 51.8F
    Courtesy of Ryan ValleeClass of 2015 NCMS
  • 20. Rhode Island Precipitation Trend
    Annual PrecipitationProvidence, RI 1933-2010
    *
    *
    Courtesy of Ryan ValleeClass of 2015 NCMS
  • 21. Rhode Island Snowfall Trend
    Seasonal SnowfallProvidence, RI 1933-2010
    *
    *
    Courtesy of Ryan ValleeClass of 2015 NCMS
  • 22. Climate Change Scenarios:Shorter snow season – less days with snow on the groundMore precipitation falling as rain prior to spring “green-up”
    Burakowski et al., 2008, JGR
  • 23. Climate Change Scenarios:Increase in 1 inch and 2 inch rainfall events
    1 inch events (1947-2007)
    2 inch events (1947-2007)
    Spierre et al., 2008
    Spierre et al., 2008
  • 24. There has been a shift in Return Frequency
    Most significant in the 25 to 100 yr recurrence interval.
  • 25. Implications:
    Impacts on the floodplain, land use, infrastructure, dam spillway requirements, drainage requirements, non-point source runoff, bridge clearances, “hardening” of critical facilities in the floodplain, property values etc…
    Flood Insurance – work to increase participation
    How much risk are we willing to insure and accept?
    Graphic courtesy of Cameron Wake
    University of New Hampshire
  • 26. The Floods of March 2010Examining Observed and Future Impacts of Increased Rainfall and Flooding
    David R. ValleeHydrologist-in-ChargeNWS/Northeast River Forecast Centerhttp://weather.gov/nerfc
    Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10

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