1) The March 2010 floods in southeastern New England were caused by a sequence of heavy rainfall events over 5 weeks that saturated the ground and led to record monthly rainfall totals of 12-18 inches. This caused major to record flooding across the region. 2) Historical climate data shows temperatures and precipitation increasing in Rhode Island, with more rain falling as heavier events. This has led to an increase in flood frequencies in the region's rivers. 3) Future climate change may exacerbate flooding risks by bringing more rain prior to spring green-up, heavier 1-2 inch rainfall events, and a shorter snow season with less snowpack to help mitigate flooding impacts. Proper planning is needed to adapt infrastructure and development to

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