David R. Vallee Hydrologist-in-Charge NWS/Northeast River Forecast Center http://weather.gov/nerfc Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10 The Floods of March 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
Presentation by Dave Vallee, Hydrologist in charge, National Weather Service.
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David R. ValleeHydrologist-in-Charge
NWS/Northeast River Forecast Centerhttp://weather.gov/nerfc
Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10
The Floods of March 2010Examining Observed and Future Impacts of Increased Rainfall and
Flooding
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
What is forecast for the 2011 Season?
Conditions Setup ACE Index Estimate
Named Storms: 12-18Hurricanes: 6-10Major Hurricanes: 3-6 (Cat 3, 4 or 5)
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)
The theme of the prevailing summer weather pattern ultimately determines our vulnerability
Point at which New Englanders needs to take action!
Providence Street – West Warwick, RI at 1030 am Wednesday 3/31/10
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?
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.
It was not caused byOne single Nor’easter or one Coastal
StormSnowmeltImproper water management
So what brought us to the tipping point during the last week of March 2010?
It was caused by:The atmospheric river – “energized” by El NinoBlocking high pressure over GreenlandA sequence of heavy rainfall events over 5
weeks Record monthly rainfall totaling 12-18 inches
Axis of each event over Pawcatuck & Pawtuxet Valleys
Saturated groundA “chuck-full” Scituate Reservoir
Designed for Water Supply not Flood Control!Swollen streams and ponds running well above
normalThe lack of nature’s grasses, flowers and trees
Pre-growing season – no Evapo-transpiration to help us out
So what brought us to the tipping point?
Major to Record flooding across southeast New England
The Blackstone ResponseDodged a huge bullet – as heaviest rains stayed south of the basin Considerable flooding on mainstem and many small streams
The Pawtuxet’s Record ResponseDramatic “urban response” in the lower basin followed by record reservoir flows from Scituate Reservoir
Pawcatuck Basin – similar responses
Pawcatuck River – Westerly, RI
Pawcatuck River – Wood River Junction
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 rainThe 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”
Historical Footnotes
The Basin itself…many twists/turns and tremendous urbanization of the lower watershed post 1968 – which corresponds to the jump in flood frequencies