# Presentation: 467571

## Trendy Perspectives inCoastal Water Leveland Hazard Implications 

**Len Pietrafesa****1**
**&**
**Tom Karl****2**
**Margaret Davidson****3**
**Dave Dickey****1**
**Lian Xie****1**
**1****North Carolina State University**
**2****NOAA NESDIS National Climatic Data Center**
**3 ****NOAA NOS Coastal Services Center**
** **

## Issues

**US coastal regions have experienced enormous growth and development **
**And are at great risk due to exposure to the impacts of present and future climate factors and weather events and rising SL**
**Potential impacts include: erosion of beaches; mass wasting of coastal bluffs; higher surge and increased property damage; increased inundation of low lying areas, particularly during storms; salt water intrusion into aquifers; etc.**
** **
**Alaska has significant coastal exposure to not only storm induced waves but sea ice as well**
**    ****But, what are the facts? Is sea level really rising along the coastlines of the US? If so, by how much? What are the trends?**

## But 1st , some historical perspective

**Modern Sea Level is believed to be rising globally at ~ 0.2 cm/yr or = to the 3****rd**** to 4****th**** fastest rate in 18K years, but US sites show .16 to .44 cm/yr or up to the 2****nd**** fastest rate  **
** **
**21,000 years before the present (YBP), glacial ice sheets covered Canada and much of the US. As a consequence of the fresh water sequestration, global sea level was > 100 meters lower than it is at present**
** **
**Then, 18,000YBP, the planetary climate system switched from cool to warm; the ocean and atmosphere began to heat up**
** **
**Subsequently the glaciers receded, the ice sheets broke up and melted and the ocean expanded due to the increased heat content**
**And sea level began to march upward, in five discernable epochs: I) very aggressive; II) aggressive; III) modest; IV) quiet; and V) the modern, which is purported to be between modest to aggressive, depending on location **

## The Documented Time History of Global Sea Level with a ballpark number for the past 85 years: But, so what?

**So**
**What**?

**Notes:**
Modern Sea Level is believed to be rising globally at ~ < or = to the 2nd fastest rate in 18K years (0.15-.45 cm/year)

18,000 years before the present (YBP), glacial ice sheets covered Canada and much of the US. As a consequence of the fresh water sequestration, global sea level was > 100 meters lower than it is at present

Then the planetary climate system switched from cool to warm; the ocean and atmosphere began to heat up

Subsequently the glaciers receded, the ice sheets broke up and melted and the ocean expanded due to the increased heat content

And sea level began to march upward, in five discernable epochs: I) very aggressive; II) aggressive; III) modest; IV) quiet; and V) the modern, which is between modest to aggressive, depending on your location

## This is “so what”. People & Property       = Fn( X, t) in coastal zones. Example: NC

**Now, back to SL. So, what affects coastal water level variability? **
**14 of the many suspects include:**
**addition of**_** fresh water due to**_** **_**melting of Alpine Glaciers & Polar Ice Sheets**_** (+) **
_**auto-compaction of ancient sediments**_** (+)**
_**compaction of deep sediments**_**, particularly in deltaic environments (+) **
_**regional to**_** **_**local isostatic rebound**_** from the last period of glacial loading (- ) **
**local to regional slumps in coastal areas due to **_**sediment discharge loading**_** (+) **
**excess precipitation (drought) and coupled watershed responses + (-) **
_**steric rises**_** (falls) of the water levels **_**of **_**adjacent **_**ocean basin(s)**_** water masses **_**due to increases**_** (decreases) **_**in**_** the **_**heat storage**_** of these water masses + (-) **
**mesoscale to synoptic scale to longer period **_**coastal winds**_** (coast to right +, left -)**
_**ocean basin**_** long **_**waves**_** (+ or -)**
**changes in **_**the coastal wave field**_** (seasonal)  **
_**management practices**_** **_**such as dikes and impoundments**_** (-) **
_**climate variability**_** (+ or -)  **
_**climate change**_** (+)**
_**BUT**_** **_**the peer reviewed literature including recent publications claim that establishing reliable trends of SL rise does not appear possible because it is very-difficult-to-determine initial and end points of observation**_

## Lets consider Representative Monthly records of Sea Level Extrema.  Q: “Trends” clearly could change as a function of time window.                        How about the Extrema or on an Annual Ave.?

**In the Charleston time series, Maxima and Minima are rising but not diverging;**
**As shown in this “box and whiskers” plot. **

**In the Charleston SL time series (left) on a yearly average basis, we note fluctuations of 20-30 cm over periods of several years to decades.** **Still no trend other than “up overall”, is identifiable and thus dificult to define.**
**So we perform a modal decomposition on the time series of SL of Pensacola (right).  Note there are 7 modes with the gravest the “trend”.**

**Monthly, seasonal, annual, 2-5 yrs,**
**10-12 yrs, 25-30 yrs and the gravest **
**Mode => a “trend”**

## Trends for a representative sampling of US SL stations

## SL Trends and Erosion Implications 

_**                                  **__**SLR        Time to 1 Foot Up & 100 feet of Erosion**_
_** **_
_**Atlantic City = .44 cm/yr   => 1 foot in 70 yrs  => 100 ft in ~46yrs**_
**Charleston   = .29 cm/yr   => 1 foot in 105 yrs => 100 ft in ~70 yrs**
**Pensacola    = .16 cm/yr   => 1 foot in 192 yrs => 100 ft in ~128 yrs**
_**Galveston     = .88 cm/yr   => 1 foot in 34  yrs => 100ft in ~  22 yrs**_
**Hilo                = .27 cm/yr   => 1 foot in 112 yrs=> 100ft in ~ 74 yrs**
**San Diego     = .17 cm/yr   => 1 foot in 177 yrs=> 100 ft in ~ 118 yrs  **
_**Cordova         = .38 cm/yr   => 1 foot in 80 yrs=> 100 ft in ~ 53 yrs**_
**Note, there are East coast, GoM and West coast high SLR and lateral erosion locales. **** **** **

## Note, the Metonic Cycle, a 19 YR period over which all 235 lunations (or phase relations between the moon, earth, sun, etc.) will reoccur on the same day of the year is missing. But, if we redo the modal decomposition, using hourly water level data, then the 19 YR Epoch shows up as the modulating envelope of Mode 2.This says that to properly measure SL at a coastal point, you need to have hourly data.  A samplingmessage. 

## Representative (record length) Annual Monthly Values of SL

**We must properly initialize Water level in surge & inundation models**
**For example: how the initial water level will effect the ultimate height of surge and distance of inundation in the Pamlico Sound system**

## Some Lessons Learned:

**1)      Present rates of SLR in US coastal waters may, overall, be 2****nd**** in rate, retrospectively to 18,000 YBP**
**2)      Hourly data are required to properly resolve all tidal constituents **
**3)      Rates of WLR vary significantly over periods of days to weeks to months to seasons to years to multiple years to multiple decades; the maximum length of time for which we have continuous records**
**4)     Maxima , Means and Minima of WL are rising but not diverging**
**5)     WLs generally stand 10-50 cm higher because of ocean basin scale steric effects during different seasons of the yea**
**6)     Basin scale waves contribute to SL multi-year variability  **
**7)     Coastal water levels are required to initialize coastal surge and inundation models; especially during storm conditions**
**8)     The existing national water level monitoring network needed to properly assess water levels locally, either over long or short **
**         ****time scales, cannot be compromised**
**9)      Water impoundment and sequestration are a cause of underestimation of true SLR**
**10)    Coastal Buyer beware**

## Funding agencies

**Funding agencies**

- NOAA NOS Coastal Services Center
- NOAA NESDIS National Climatic Data Center
-                 Via the
- Climate & Weather Impacts
-                   on
- Society & the Environment
-        CWISE Co-Operative

## Thank You