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.

NERFC Hydromet Self-briefing Page

http://www.weather.gov/nerfc Click on “Self Brief Page”

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

Royal Mill Dam

Natic Dam

Arctic Dam

Pawtuxet River Flood Frequency

Post Mall and I-95 construction

Blackstone River Flood History

Post USACE Flood Control Product

Construction

1930 1940 1950 1960 1970 1980 1990 2000 2010 202046

47

48

49

50

51

52

53

54

55

Annual Temperature

Linear (Annual Temperature)

Year

Tem

pre

ture

(degre

es

F)

Trend line: y=1/61x +18.65

Prediction for 2020= 51.8F

*

*

Courtesy of Ryan ValleeClass of 2015 NCMS

Rhode Island Temperature TrendAnnual Temperature

Providence, RI 1933-2010

1930 1940 1950 1960 1970 1980 1990 2000 2010 202020

25

30

35

40

45

50

55

60

65

70

Annual Precipitation

Year

Pre

cip

itati

on

(in

ch

es)

Trend line: y = 7/62x – 177.81

Prediction for 2020 = 50.3 in.

*

*

Courtesy of Ryan ValleeClass of 2015 NCMS

Rhode Island Precipitation TrendAnnual Precipitation

Providence, RI 1933-2010

1 inch events (1947-2007) 2 inch events (1947-2007)

Spierre et al., 2008 Spierre et al., 2008

Climate Change Scenarios:Increase in 1 inch and 2 inch rainfall events

1 Day Return period TP-40 from 1961 NRCC Draft 2010 http://www.precip.net

Event in years Inches in 24 hours Inches in 24 hours

2 3.25 3.26

10 4.75 4.86

25 5.50 6.15

50 6.15 7.30

100 7.00 8.70

Most significant in the 25 to 100 yr recurrence

interval.

There has been a shift in Return Frequency

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 WakeUniversity of New Hampshire

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