www.csiro.au erin e. peterson postdoctoral research fellow csiro mathematical and information...
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www.csiro.au
Erin E. Peterson
Postdoctoral Research Fellow
CSIRO Mathematical and Information Sciences Division
Brisbane, Australia
May 18, 2006
Regional GIS-based Geostatistical Models for Stream Networks
The work reported here was developed under STAR Research Assistance Agreement CR-829095 awarded by the U.S.
Environmental Protection Agency (EPA) to Colorado State University. This presentation has not been formally reviewed by
EPA. EPA does not endorse any products or commercial services mentioned in this presentation.
Space-Time Aquatic Resources Modeling and Analysis Program
This research is funded by
U.S.EPA凡Science To AchieveResults (STAR) ProgramCooperativeAgreement # CR -829095
This research is funded by
U.S.EPAScience To AchieveResults (STAR) ProgramCooperativeAgreement # CR -829095
Dr. David M. TheobaldNatural Resource Ecology LabDepartment of Recreation & TourismColorado State University, USA
Dr. N. Scott UrquhartDepartment of StatisticsColorado State University, USA
Dr. Jay M. Ver HoefNational Marine Mammal Laboratory, Seattle, USA
Andrew A. MertonDepartment of StatisticsColorado State University, USA
Collaborators
Overview
Introduction~
Background~
Develop and compare geostatistical models
~Visualizing model predictions
~Current and future research in
SEQ
Challenges
Challenges are similar to states attempting to comply with the Clean Water Act
Anadromous Waters Catalog (AWC)
Large number of water bodies within AK
~ 20,000 unidentified anadromous water bodies
Need spatially explicit, unambiguous field observations of anadromous fish
Cost (time and $$) of field surveys is high
“… We recognize a pressing need for approaches that predict the distribution of salmon in Alaska’s extensive unsurveyed freshwaters.”
My Goal
Demonstrate a geostatistical methodology based on
Coarse-scale GIS data
Field surveys
Predict stream characteristics for individual segments throughout a region
How are geostatistical models different from traditional statistical models?
Traditional statistical models (non-spatial)
Residual error (ε) is assumed to be uncorrelated
ε = unexplained variability in the data
Geostatistical models
Residual errors are correlated through space
Spatial patterns in residual error resulting from unidentified process(es)
Model spatial structure in the residual error
Explain additional variability in the data
Generate predictions at unobserved sites
Y X
( ) ( ) ( )Y s X s s
Geostatistical Modeling
Fit an autocovariance function to data Describes relationship between observations based on separation distance
Separation Distance
Sem
ivar
ian
ce
Sill
Nugget Range
10000
0
103 Autocovariance Parameters
1) Nugget: variation between sites as separation distance approaches zero
2) Sill: delineated where semivariance asymptotes
3) Range: distance within which spatial autocorrelation occurs
Distance Measures and Spatial Relationships
Straight Line Distance (SLD)
As the crow flies
A
B
C
Symmetric Hydrologic Distance (SHD)
As the fish swims
A
B
C
Distance Measures and Spatial Relationships
Weighted asymmetric hydrologic distance (WAHD)
As the water flows
Incorporate flow direction & flow volume
A
B
C
Distance Measures and Spatial Relationships
Ver Hoef, J.M., Peterson, E.E., and Theobald, D.M. (2006) Spatial Statistical Models that Use Flow and Stream Distance, Environmental and Ecological Statistics, to appear.
Fit a mixture of covariances
A
B
C
Cressie, N., Frey, J., Harch, B., and Smith, M.: 2006, ‘Spatial Prediction on a River Network’, Journal of Agricultural, Biological, and Environmental Statistics, to appear.
Based on more than one distance measure
Distance Measures and Spatial Relationships
Site’s relative influence on other sites Dictates form and size of spatial neighborhood
Important because… Impacts accuracy of the geostatistical model predictions
Distance measure influences how spatial relationships are represented in a stream network
SHD WAHDSLD
Distance Measures and Spatial Relationships
Demonstrate how a geostatistical methodology can be used to identify ecologically significant waters
Example:
Develop and compare geostatistical models for DOC
Predict regional DOC levels
Identify the spatial location of stream segments with high levels of DOC
Dissolved Organic Carbon (DOC) Example
N 0 20
Kilometers
n Min 1st Qu. Median Mean 3rd Qu. Max σ2312 0.6 1.2 1.7 1.9 2.7 15.9 1.8
N 0 20
Kilometers
0 20
Kilometers
n Min 1st Qu. Median Mean 3rd Qu. Max σ2312 0.6 1.2 1.7 1.9 2.7 15.9 1.8n Min 1st Qu. Median Mean 3rd Qu. Max σ2
312 0.6 1.2 1.7 1.9 2.7 15.9 1.8
N 0 20
Kilometers
n Min 1st Qu. Median Mean 3rd Qu. Max σ2312 0.6 1.2 1.7 1.9 2.7 15.9 1.8
N 0 20
Kilometers
0 20
Kilometers
n Min 1st Qu. Median Mean 3rd Qu. Max σ2312 0.6 1.2 1.7 1.9 2.7 15.9 1.8n Min 1st Qu. Median Mean 3rd Qu. Max σ2
312 0.6 1.2 1.7 1.9 2.7 15.9 1.8
Study Area
Maryland Biological Stream Survey (MBSS) Data
Create data for geostatistical modeling
1. Calculate watershed covariates for each stream segment2. Calculate separation distances between sites
SLD, Asymmetric hydrologic distance (AHD)3. Calculate the spatial weights for the WAHD4. Convert GIS data to a format compatible with statistics software
FLoWS website: http://www.nrel.colostate.edu/projects/starmap
1 2
3
1 2
3
SLD
1 2
3
SHD AHD
Functional Linkage of Watersheds and Streams (FLoWS)
Spatial Weights for WAHD
Proportional influence (PI): influence of each neighboring survey site on a downstream survey site Weighted by catchment area: Surrogate for flow volume
1. Calculate the PI of each upstream segment on segment directly downstream
2. Calculate the PI of one survey site on another site Flow-connected sites Multiply the segment PIs
BA
C
Watershed Segment B
Watershed Segment A
Segment PI of A
Watershed Area A
Watershed Area A+B=
A
BC
DE
F
G
H
survey sitesstream segment
Spatial Weights for WAHD
Proportional influence (PI): influence of each neighboring survey site on a downstream survey site Weighted by catchment area: Surrogate for flow volume
1. Calculate the PI of each upstream segment on segment directly downstream
2. Calculate the PI of one survey site on another site Flow-connected sites Multiply the segment PIs
A
BC
DE
F
G
H
Site PI = B * D * F * G
Spatial Weights for WAHD
Proportional influence (PI): influence of each neighboring survey site on a downstream survey site Weighted by catchment area: Surrogate for flow volume
1. Calculate the PI of each upstream segment on segment directly downstream
2. Calculate the PI of one survey site on another site Flow-connected sites Multiply the segment PIs
Data for Geostatistical Modeling
Distance matrices
SLD, AHD
Spatial weights matrix
Contains flow dependent weights for WAHD
Watershed covariates
Lumped watershed covariates
Mean elevation, % Urban
Observations
MBSS survey sites
Geostatistical Modeling Methods
Autocorrelation Function SLD WAHD
Exponential
Spherical
Mariah
Hole Effect
Linear with Sill
Rational Quadratic
Fit the correlation matrix for SLD and WAHD models
Maximized profile-log likelihood function Estimate model parameters
Comparison within model set Spatial AICC
Comparison between model set Universal kriging MSPE
R2 = 0.7221
0
18
0 5 10 15Observed DOC mg/l
Pre
dic
ted
DO
C m
g/l r2 = 0.7221R2 = 0.7221
0
18
0 5 10 15Observed DOC mg/l
Pre
dic
ted
DO
C m
g/l r2 = 0.7221
r2 Observed vs. Predicted values
SLD Mariah Model
1 influential site r2 without site = 0.66
Spatial Patterns in Model Fit
Squared Prediction Error (SPE)
Generate Model Predictions
Prediction sites Study area
– 1st, 2nd, and 3rd order non-tidal streams– 3083 segments = 5973 stream km
ID downstream node of each segment– Create prediction site
Generate predictions and prediction variances
SLD Mariah model Universal kriging algorithm
DOC Predictions (mg/l)
Weak Model Fit
Strong Model Fit
Apply this methodology to salmon or salmon habitat
Identify habitat conditions necessary for spawning, rearing, or migration of anadromous fish Based on ecological & biological knowledge
Identify watershed conditions that may influence those conditions Watershed geology type ~ substrate type Derive watershed characteristics using GIS/remote sensing
Generate predictions and estimates of uncertainty for potential salmon habitat
Categorize predictions into low, medium, or high status Probability of supporting anadromous fish
Implications for Anadromous Fish Conservation
Tradeoff between cost-efficiency and model accuracy One model can be used throughout a large region Regions may be ecologically unique May need to generate separate models for AWC regions
Allocate scarce sampling resources efficiently Target areas with a high probability of supporting anadromous fish Identify areas where more information would be useful
Implications for Anadromous Fish Conservation
Advantages of GIS
Identify spatial patterns in model fit
Evaluate habitat at multiple scales Feature scale and regional scale Help prioritize fish habitat restoration Help prioritize land/conservation easement
acquisitions
Easily communicate with community, environmental, and government groups
Implications for Anadromous Fish Conservation