Tom Ravens and Jon Allen, Univ. of Alaska Anchorage Projection of Storm Surge Impacts on the YK Delta Vegetation under Climate Change Kashunuk R. 10 km 10 km Tom Ravens and Jon Allen, Univ. of Alaska Anchorage

Current vegetation Projected vegetation, 40 cm SLR Projected vegetation, 80 cm SLR Projected vegetation, 120 cm SLR

Research Goal: Project YK Delta vegetation change due to storm surges – enhanced by sea level rise Tasks: Develop and validate a storm surge and inundation model Identify a number of representative storms from the past 20 years Model these storms and their inundation under present climate conditions Re-model these storms assuming 3 sea level rise scenarios Compute an inundation index from each model run Compute an annual inundation index based on inundation indices from selected storms (for each scenario) Establish the relationship between annual index and vegetation type under present climate Infer changes in vegetation type under a future climate based on projected changes in annual inundation index

Storm surge modeling - course grid model domain YK Delta

Fine-grid model domain and bathymetry and topographic data Kashunuk River Hooper Bay

Assessment of course-grid (ADCIRC) model at Nome ---- measured water level, modeled water level 2011 storm Good performance 2005 storm Marginal performance

Assessment of course-grid ADCIRC model performance at the Nome site Date of storm Assessment Nov. 2011 Good Nov. 2009 Bad (model missed peak of this small storm) Oct. 2006 Sept. 2005 Marginal - model 0.5 m too low, measured peak at Nome = 2.7 m Oct. 2004 Oct. 1992 Marginal - model 0.5 m too low, measured peak at Nome = 2.3 m

Assessment of course-grid/fine grid model system for coastal water level 2009 storm Good performance 2011 storm Marginal performance

Reasonable performance Assessment of course-grid/fine grid model system for coastal flooding extent 2006 storm Reasonable performance (over-calculation) 2005 storm Marginal performance (under-calculation)

Conclusions from model assessment phase Overall performance of model system was below expectations. For ecological modeling purposes, the forcing on the ocean boundary of the fine-grid model was adjusted to get good results. Accurate simulations of storms from 2005, 2006, 2009, and 2011 were obtained. The 2005, 2009, and 2011 storms were assigned return periods of: 11, <2, and 3.5 years, respectively, based on the return period analysis.

Return period calculation – based on surge height and volume Ordering of storms based on peak surge height at coast near center of domain Ordering of storms based on peak volume of flooding 2005 storm is 14 year storm 2005 storm is 11 year storm

Tabular return period data Return period based on volume: Water level and flood volume for different return periods: Storm Return period (yr) 1995 Oct 15.25 2004 Oct 11.04 2005 Sept 10.78 1996 Oct 6.03 1992 Oct 5.03 2011 Nov 3.49 1996 Nov 2.00 Return Period (yr) Water level at Hooper Bay offshore node (m) Max Instantaneous Surge Volume (108 m3) 2 3.00 7.8 5 3.39 18.0 10 3.65 24.7 20 3.90 31.2 50 4.22 39.5 100 4.46 45.7

<2 year storm (2009), 2.5 m 10.8 year storm (2005), 3.7 m Nov. 2011

GMT AK time

Storm Inundation Index (<2 year storm, 2009) Legend [m-days]

Storm Inundation Index (3.5 year storm, 2011) Legend [m-days]

Storm Inundation Index (10.8 year storm, 2005) Legend [m-days]

Annual inundation index – current climate [based on weighted average of storm indices, (½ x 2 yr + 1/8 x 8 yr + 1/12 x 12 yr + 1/50 x 50 yr) x 0.729] Legend [m-days/yr]

Correspondence between annual inundation index and vegetation type under current climate Legend [m-days/yr] Annual Inundation index Legend [vegetation type] Vegetation type

Area for developing relationship between annual inundation index and vegetation type Selected due to local LiDAR coverage and high elevation-vegetation type correlation

Relationship between Annual Inundation Index and Vegetation Type [m-days/yr] Vegetation Type

Slightly brackish-brackish cutoff not clearly defined, thus potentially significant misclassification. Due to low counts of saline points, brackish-saline cutoff inexact.

Current Annual Inundation Index (AII) Annual Inundation Index, 40 cm SLR AII (m day / yr) Annual Inundation Index, 120 cm SLR Annual Inundation Index, 80 cm SLR

Current vegetation Projected vegetation, 40 cm SLR Projected vegetation, 80 cm SLR Projected vegetation, 120 cm SLR

Conclusions Annual inundation index well-correlated with vegetation type. Calculated annual inundation based on sea level rise scenarios is a reasonable basis for projecting vegetation change in the future. Significant shifts in vegetation are expected with sea level rise considered.

Future Work Finalize work on return period analysis. Finalize work on storm surge modeling. Examine the relationship between inundation index and bird/nest abundance. Model and analyze pond water quality. Model and analyze geomorphic change. Real time forecasting of flooding on YK Delta and in Norton Sound for DHS

ADAC coastal inundation forecast– big view

ADAC coastal inundation forecast

Forecast data at a point

Collaborators and supporters Craig Ely, John Terenzi (USGS, Alaska) Torre Jorgenson (Ecoscience) Raymond Chapman, Ken Eisses (USACE) Steven Gray (USGS AK Climate Science Center) Joel Reynolds, Karen Murphy (Western Alaska Landscape Conservation Cooperative) Sarah Saalfeld (USFWS)

Questions?