Storm clouds with the right internal conditions can generate large numbers of electric chargesseparated by miles of air. When and where cloud leaders and ground streamers will connect is impos-sible to precisely predict. The strength of ground streamers (ground field enhancement) can be estimatedbased upon different objects or neighborhoods on the ground. Risk assessments are concentrated onground streamer strength while leader / streamer connectivity is highly variable depending upon the storm.

Ground streamer strength (field enhancement) is based upon many factors which can be increasedto a point where any cloud leaders in the area (i.e. within 5 to 6 times tree height above the tree) willinterconnect and exchange charges. A tree's topographic position and height above surrounding objects orstructures play crucial roles in determining where lightning will strike. Isolated, tall trees would have thepotential for strong ground streamer strength and serve as a conduit of charge exchange exceeding simplerandom probabilities. Valuable trees along the path of potential lightning strikes, where risk is basedupon ground streamer strength factors, should be evaluated.

Three simple and quick risk analysis methods are presented here. They are based on an educa-tional summary of lightning risk factors in trees and neither should be used as a single source in determin-ing lightning conduction system requirements for trees.

Height MethodThe first assessment method for gauging lightning risk to trees is the Coder Tree Height Assessment

for Lightning Risk used to help tree health care providers in discussions with clients as to whether a treelightning conduction system should be installed. This risk assessment process is based only upon historiclightning ground strike information for the tree location (i.e. annual lightning ground strike density persquare mile), and tree height. (derived from Bazelyan & Raizer 2000)

Figure 1 is a graph comparing tree heights in feet with lightning ground strike per square mile peryear at four different risk levels. Risk levels are provided for 1 in 25 years (4%), 1 in 50 years (2%), 1 in100 years (1%), and a 1 in 200 years (0.5%) chance of a lightning strike. Higher risk values, like 1 in 10years (10%) and 1 in 5 years (20%), are considered so likely to occur, risk assessment is not required.The fewer lightning strikes per year at any location, the greater tree height at which various risk levels of astrike occur.

StrikStrikStrikStrikStrike Risk e Risk e Risk e Risk e Risk AssessmentsAssessmentsAssessmentsAssessmentsAssessmentsby Dr. Kim D. Coder, Professor of Tree Biology & Health Care

In compliance with federal law, including the provisions of Title IX of the Education Amendments of 1972, Title VI of the Civil Rights Act of 1964,Sections 503 and 504 of the Rehabilitation Act of 1973, and the Americans with Disabilities Act of 1990, the University of Georgia does not

discriminate on the basis of race, sex, religion, color, national or ethnic origin, age, disability, or military service in its administration ofeducational policies, programs, or activities; its admissions policies; scholarship and loan programs; athletic or other University-administered

programs; or employment. In addition, the University does not discriminate on the basis of sexual orientation consistent with the Universitynon-discrimination policy. Inquiries or complaints should be directed to the director of the Equal Opportunity Office, Peabody Hall, 290 South

Jackson Street, University of Georgia, Athens, GA 30602. Telephone 706-542-7912 (V/TDD). Fax 706-542-2822.

WSFNR13-18 November 2013

Trees & Lightning Series

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 2

Figure 2 shows the great risk variation in tree heights. Notice above a lightning strike density ofabout 18 ground strikes per square mile per year, there is little difference in tree risk based upon treeheight. Below this strike density, tree height differences do differentiate risk levels more clearly.

Figure 3 provides heights (in feet) for single, isolated trees at the greatest risk for lightning strikesdepending upon tree location (i.e. lightning ground strike density per square mile per year.) For example,if your location sustains 15 lightning ground strikes per square mile per year, an 81 feet tall single isolatedtree would fall into the 10% annual risk category and is considered a super high risk of a lightning strike.If a similar 80 feet tall tree in the same area is at least 35 feet above surrounding structures and othertrees, then this tree would fall into 2% annual risk category and is considered only a moderate risk of alightning strike.

Uman Ground Collection MethodFigure 4 provides another way of considering how tree height impact the number of lightning

strikes for a given strike density. This method represents the collection area of a tree, or the enhancedarea for lightning strikes based upon added tree height. Figure 5 illustrates how the tree collection area iscalculated using tree height and crown diameter. Four times (4X) tree height is used traditionally forestimating lightning strikes to trees under 50 feet tall. Six times (6X) tree height is used as an area calcu-lation for international lightning protection standards and trees over 50 feet. Figure 6 provides exampleprobability of tree lightning strikes using N=15 lightning strikes per square mile per year, and a crowndiameter of 30 feet. (derived from Uman 2008). Note how lightning strike potential greatly increaseswith tree height above 45 feet.

Coder-Cripe MethodThe second assessment method for gauging lightning risk to trees is the Coder-Cripe Ground Effects

Lightning Risk Assessment method. This assessment uses a number of lightning strike risk factors(i.e. enhanced electric field -- ground streamer strength factors) associated with trees. Tree height, rela-tive height of a tree within its surroundings, location on landscape, closeness of neighboring trees andstructures, and historic number of ground strikes per square mile per year are all incorporated. The resultis a simple assessment for determining if a lightning conduction system is warranted. It does not (can not)include tree values or benefit / cost analysis. This assessment is a training guide for determining potentiallightning strike probabilities on trees. (based partially on Robert E. Cripe's work).

DeterminationsTo use this assessment aid, you will need several pieces of information about the assessed tree and

site. An accurate tree height and neighboring structure height are essential. Use a clinometer, hand altim-eter, or height stick with a 100 feet tape to record height and distance measures.

Figure 7 represents risk factor #1 -- where is the tree located topographically in the landscape.Higher locations, compared with low growth sites are more likely to have strong ground streamerstrengths. Large scale, landscape level positions which accentuate a tree’s effective height and groundstreamer strength carry higher risks. Trees on hilltops will usually have stronger ground streamer strengththan trees in valley bottoms. Determine the risk percentage closest to the assessed tree's topographiclocation.

Figure 8 represents risk factor #2 -- relative height of the tree crown. Determine relative treeheight compared with neighboring trees. The more a tree crown rises above neighboring trees, the stron-ger its potential ground streamer strength. This figure shows tree crowns and names of crown classes(relative height values). The classic crown class descriptions are used to determine if the assessed tree is

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 3

taller (an emergent crown class) than its surrounding tree neighbors. Pick the risk percentage closest tothe assessed tree's crown class. Single isolated trees with no surrounding trees would be assessed at100%.

Figure 9 represents risk factor #3 -- tree crown openness or view aspect. Determine how open atree crown is from the sides. Trees open to water, fields, large open spaces, or facing areas with vegeta-tion significantly shorter in height, will leave the sides of their crowns open and more likely to producestrong ground streamers. This figure shows tree crowns from above clustered around the assessed tree(i.e. the darkest circle) and various levels of openness of the assessed tree crown. Risk percent is equalto degrees of openness between 0o & 360o divided by 3.6. Figure 10. Single trees standing alone areopen on all sides and tend to have the strongest ground streamer strength. As neighboring trees close in ondifferent sides, the openness risk factor declines. A risk percentage for the degree of tree crown opennessshould be determined.

Figure 11 represents risk factor #4 -- relative height of other structures in the neighborhood. Adirect measure of the single tallest structure or tree in the neighborhood is compared to the assessed tree.The neighborhood distance on the ground is a radius three times assessed tree height (3 X tree height)away from the assessed tree. Within this neighborhood distance, calculate the relative height differencefor the single tallest structure or tree. The taller the tree is in its neighborhood, the stronger its potentialground streamer strength. Figure 12. A risk percentage for how tall the assessed tree is compared to thetallest structure in the neighborhood should be determined.

Figure 13 represents risk factor #5 -- proximity of human or property targets. When lightningstrikes a tree, collateral damage can result. The risk of a tree lightning strike impacting structures, elec-tronics, animals and humans in the vicinity is a major concern. A risk assessment must determine thespacial relationship between trees and these targets. The closer and taller the assessed tree is to a target,the stronger ground streamer potential, and the more likely target damage and injuries (possibly death)may occur if lightning strikes. Structures surrounded by, or overhung with, tree branches should have theirown lightning protection system. The distances listed for risk assessment are based upon radial distancesaway from the base of the assessed tree stem at the ground surface. A risk percentage for collateraldamage to targets close to the assessed tree should be determined.

Once the first five risk factors have been determined, the percentage numbers (not decimal per-cents) should be added together. The total sum should be divided by 500 yielding a value < 1.0. Theresult is called a Composite Risk Factor since it combines or averages the first five risk factors together.Figure 14.

Taking ChancesFigure 15 represents risk factor #6 -- annual lightning strike probability. Different places across

globe have different lightning strikes per square mile per year. The map represents the number of lightningstrikes per square mile per year for the Southeastern United States. This map provides the lightning strikenumber to be used in the calculation for Risk Factor #6. The other value needed is the height of the tree.These two values are placed in the following formula:

Annual Lightning Strike Probability =

lightning strike number X [3.142 X ((tree height in feet) X 3)2 / (5,280)2 ]

The Annual Lightning Strike Probability value represents a risk value for a single tree standing alone in aflat landscape with nothing taller in its neighborhood. An Annual Lightning Strike Probability risk factorshould be determined.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 4

The Composite Risk Factor (determined from Risk Factors #1 - #5) should be multiplied by theAnnual Lightning Strike Probability (Risk Factor #6). The result is the Total Tree Lightning Strike RiskValue. Figure 16. If the Total Tree Lightning Strike Risk Value is greater than 0.05, then there is greaterthan a 1 in 20 chance a tree may be struck by lightning each year. This is considered a severe risk of treedamage. If the Total Tree Lightning Strike Risk Value is 0.01, a 1 in 100 chance exists a tree may bestruck by lightning each year. This is considered a low risk. Figure 17.

Unfortunately this risk assessment does not include expected tree life-span, or historic / culturalvalues of the tree. A tree expected to live another 300 years, and culturally valuable, would have a muchgreater risk, and much higher remorse factor if lost, than this assessment tool would determine. A TreeLightning Risk Assessment Worksheet is provided in Figure 18.

Fighting MythsThere has developed over many years a series of tree associated lightning protection concepts.

Figure 19 shows the work of Makela's team in field testing these traditional ideas. The two fundamentalideas are: 1) when trees are most likely to be struck; and, 2) lightning attributes which cause more treedamage. Some of these traditional concepts are supported by field observations. One specifically re-quires more research -- in a forest landscape, the tallest tree is not most likely to be struck.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 5

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

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00000 10 10 10 10 10 20 20 20 20 20 30 30 30 30 30 40 40 40 40 40 50 50 50 50 50

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Figure 1: Risk level for tree lightning strikes based on treeheight in feet across lightning density values measuredin ground strikes per square mile per year.(derived from Bazelyan & Raizer 2000)

lightning glightning glightning glightning glightning grrrrround strikound strikound strikound strikound strikesesesesesper squarper squarper squarper squarper square mile per ye mile per ye mile per ye mile per ye mile per yearearearearear

LightningLightningLightningLightningLightningStrikStrikStrikStrikStrikeeeee

ProbabilityProbabilityProbabilityProbabilityProbability

4% per year4% per year4% per year4% per year4% per year(high risk)(high risk)(high risk)(high risk)(high risk)

2% per year2% per year2% per year2% per year2% per year(moderate risk)(moderate risk)(moderate risk)(moderate risk)(moderate risk)

1% per year1% per year1% per year1% per year1% per year(low risk)(low risk)(low risk)(low risk)(low risk)

0.5% per year0.5% per year0.5% per year0.5% per year0.5% per year(v(v(v(v(vererererery loy loy loy loy low risk)w risk)w risk)w risk)w risk)

○ ○ ○ ○ ○ ○ ○ ○ ○

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 6

100

80

60

40

20

0

trtrtrtrtree heightee heightee heightee heightee height(f(f(f(f(feet)eet)eet)eet)eet)

00000 10 10 10 10 10 20 20 20 20 20 30 30 30 30 30 40 40 40 40 40 50 50 50 50 50lightning glightning glightning glightning glightning grrrrround strikound strikound strikound strikound strikesesesesesper squarper squarper squarper squarper square mile per ye mile per ye mile per ye mile per ye mile per yearearearearear

Figure 2: Average risks for tree heights (between high andvery low risk) across lightning density value measured inground strikes per square mile per year. Dotted linesrepresent 30 feet height and 18 ground strikes.(derived from Bazelyan & Raizer 2000)

gggggrrrrreaeaeaeaeat risk dift risk dift risk dift risk dift risk difffffferererererenceenceenceenceenceby tree heightby tree heightby tree heightby tree heightby tree height

little diflittle diflittle diflittle diflittle difffffferererererence in trence in trence in trence in trence in treeeeeeeeeerisk lerisk lerisk lerisk lerisk levvvvvels bels bels bels bels by heighty heighty heighty heighty height

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 7

Figure 3: Single, isolated tree heights in feet within thegreatest risk catagories for lightning strikes dependingupon tree location (lightning ground strike density persquare mile per year.)

lightninglightninglightninglightninglightning strik strik strik strik strikeeeee lightning strik lightning strik lightning strik lightning strik lightning strike anne anne anne anne annual risk leual risk leual risk leual risk leual risk levvvvvelelelelel density density density density density(mile(mile(mile(mile(mile22222/year)/year)/year)/year)/year) 20% 20% 20% 20% 20% 10% 10% 10% 10% 10% 4% 4% 4% 4% 4% 2%2%2%2%2%

2 2 2 2 2 -- -- -- -- -- ---------- 140 140 140 140 140 9595959595 5 5 5 5 5 -- -- -- -- -- 140 140 140 140 140 85 85 85 85 85 60606060601010101010 140140140140140 9595959595 60 60 60 60 60 40404040401515151515 110110110110110 8080808080 50 50 50 50 50 35353535352020202020 95 95 95 95 95 7070707070 40 40 40 40 40 3030303030

2525252525 85 85 85 85 85 6060606060 35 35 35 35 35 25252525253030303030 80 80 80 80 80 5555555555 35 35 35 35 35 25252525253535353535 70 70 70 70 70 5050505050 30 30 30 30 30 20202020204040404040 65 65 65 65 65 4545454545 30 30 30 30 30 20202020204545454545 65 65 65 65 65 4545454545 25 25 25 25 25 2020202020risk lerisk lerisk lerisk lerisk levvvvvels =els =els =els =els = sesesesesevvvvvererererere super highe super highe super highe super highe super high high high high high high moderate moderate moderate moderate moderate

Coder Tree Height Assessment for Lightning Risk

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 8

Collection Collection Collection Collection Collection ArArArArArea ofea ofea ofea ofea of TTTTTrrrrree =ee =ee =ee =ee =CA in squarCA in squarCA in squarCA in squarCA in square miles =e miles =e miles =e miles =e miles =

(( tr(( tr(( tr(( tr(( tree heightee heightee heightee heightee heightftftftftft X Z ) + X Z ) + X Z ) + X Z ) + X Z ) +crcrcrcrcrooooown diameterwn diameterwn diameterwn diameterwn diameterftftftftft ) ) ) ) )22222

35,514,000.35,514,000.35,514,000.35,514,000.35,514,000.

Z = 4 (trZ = 4 (trZ = 4 (trZ = 4 (trZ = 4 (traditional vaditional vaditional vaditional vaditional value & tralue & tralue & tralue & tralue & trees <50ft)ees <50ft)ees <50ft)ees <50ft)ees <50ft)Z = 6 (interZ = 6 (interZ = 6 (interZ = 6 (interZ = 6 (internananananational standartional standartional standartional standartional standards & trds & trds & trds & trds & trees >50ft)ees >50ft)ees >50ft)ees >50ft)ees >50ft)

CACACACACAsq.mi.sq.mi.sq.mi.sq.mi.sq.mi. X N X N X N X N X Nsq.mi. per yearsq.mi. per yearsq.mi. per yearsq.mi. per yearsq.mi. per year = = = = =

trtrtrtrtree strikee strikee strikee strikee strikes per yes per yes per yes per yes per yearearearearear.....N = annN = annN = annN = annN = annual nual nual nual nual number ofumber ofumber ofumber ofumber of lightning strik lightning strik lightning strik lightning strik lightning strikes per milees per milees per milees per milees per mile22222

1 / tr1 / tr1 / tr1 / tr1 / tree strikee strikee strikee strikee strikes per yes per yes per yes per yes per year =ear =ear =ear =ear =yyyyyearearearearears betws betws betws betws between treen treen treen treen tree strikee strikee strikee strikee strikeseseseses.....

Figure 4: Tree collection area for estimating number oflightning strikes to trees of different heights over time.

(derived from Uman 2008)

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 9

Figure 5: Diagram of tree collection area for estimatingnumber of lightning strikes to trees of different heights. Z = 4.

(derived from Uman 2008)

2ht2ht2ht2ht2ht 1ht1ht1ht1ht1ht 1ht 2ht 1ht 2ht 1ht 2ht 1ht 2ht 1ht 2ht1ht1ht1ht1ht1ht

CDCDCDCDCDside viewside viewside viewside viewside view

top viewtop viewtop viewtop viewtop view

1ht1ht1ht1ht1ht 2ht2ht2ht2ht2ht 3ht 4ht 3ht 4ht 3ht 4ht 3ht 4ht 3ht 4ht

1ht

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t 4

ht

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t 4

ht

3ht

4ht

3h

t 4

ht

CDCDCDCDCD(4ht

ft + CD

ft)2 / 35,514,000 =

tree collection areasq. miles

treetreetreetreetree

treetreetreetreetree

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 10

FigureFigure 6: Tree lightning strikes determined by tree collection

area for various tree heights using 15 annual lightningstrikes per square mile and crown diameter of 30 feet.(derived from Uman 2008)

tree number of years height strikes between (feet) per year strikes

10 0.002 483 20 0.005 196 30 0.009 105 40 0.015 66 50 0.022 45 60 0.064 16

70 0.086 12 80 0.11 9 90 0.14 7100 0.17 6110 0.20 5120 0.24 4

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 11

Figure 7: Risk Factor #1 --Topographic Location in Landscape.

Determine where on the landscape tree is growing. Select riskpercentage closest to assessed tree's topographic location.

= topographic position of tree in landscape

= = = = = 100%100%100%100%100%

= = = = = 85%85%85%85%85%

= = = = = 60%60%60%60%60%

= = = = = 25%25%25%25%25%

= = = = = 1%1%1%1%1%

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 12

= tree crown class

emeremeremeremeremergggggententententent100%100%100%100%100%

co-dominantco-dominantco-dominantco-dominantco-dominant60%60%60%60%60%

interinterinterinterintermediamediamediamediamediatetetetete20%20%20%20%20%

supprsupprsupprsupprsuppressedessedessedessedessed1%1%1%1%1%

Figure 8: Risk Factor #2 --Relative Tree Height

Determine relative tree height compared with neighboring trees.Select risk percentage closest to assessed tree's crown class.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 13

Figure 9: Risk Factor #3 --Tree Openness

Determine how open tree crown is on sides compared with othersurrounding trees. Shown are tree crowns viewed from above with assessed

tree (filled circle) and neighboring trees (open circles).Select risk percentage closest to assessed tree's crown openness.

360360360360360ooooo

100%100%100%100%100%315315315315315ooooo

88%88%88%88%88%229229229229229ooooo

64%64%64%64%64%

166166166166166ooooo

46%46%46%46%46%

120120120120120ooooo

33%33%33%33%33% 6767676767ooooo

19%19%19%19%19%

2727272727ooooo

8%8%8%8%8%00000ooooo

1%1%1%1%1%

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 14

0 0 0 0 0 2020202020 4040404040 6060606060 8080808080 100 100 100 100 100trtrtrtrtree openness risk (%)ee openness risk (%)ee openness risk (%)ee openness risk (%)ee openness risk (%)

360360360360360

300300300300300

240240240240240

180180180180180

120120120120120

6060606060

00000

trtrtrtrtree opennessee opennessee opennessee opennessee openness(de(de(de(de(degggggrrrrrees)ees)ees)ees)ees)

Figure 10: Risk Factor #3 - Tree OpennessGraphical determination of tree crown openness and risk of lightning strike.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 15

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Figure 11: Risk Factor #4 --Relative Neighborhood Height Differences

Measure height of single tallest structure or tree within three (3) treeheights of assessed tree. The taller a tree is in its neighborhood, the

stronger its ground streamer strength.

treetreetreetreetreeheightheightheightheightheight

HTHTHTHTHT

1HT1HT1HT1HT1HT 2HT2HT2HT2HT2HT 3HT3HT3HT3HT3HT

1HT1HT1HT1HT1HT 2HT 2HT 2HT 2HT 2HT 3HT3HT3HT3HT3HT

TTTTTOPOPOPOPOPVIEWVIEWVIEWVIEWVIEW

SIDESIDESIDESIDESIDEVIEWVIEWVIEWVIEWVIEW

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 16

Figure 12: Risk Factor #4 --Relative Neighborhood Height Differences

Measure height of single tallest structure or tree withinthree (3) tree heights of assessed tree. The taller a tree is inits neighborhood, the stronger its ground streamer strength.

number of times risk taller than assessment assessed tree value (%)

2.5 times taller 2%2.0 times taller 10%1.5 times taller 25%1.25 times taller 55%

same height 80%

shorter 100%

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 17

assessedtree position risk

relative to target value (%)

tree as tall / taller & touching 100%

overhanging target 95%

within 1/2 tree height 90%within 1 tree height 80%within 2 tree heights 60%within 3 tree heights 25%

beyond 3 tree heights 1%

Figure 13: Risk Factor #5 --Tree Target Proximity

Risk of lightning strike impacting structures, electronics,animals and humansin vicinity. Risk assessment must determine spatial relationship between treesand potential targets. Height distances listed are based upon radial distances

away from base of assessed tree stem.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 18

Figure 14: Tree Lightning Risk Assessment(Part A of three calculations)

A) RA) RA) RA) RA) Recorecorecorecorecord all assessed vd all assessed vd all assessed vd all assessed vd all assessed values falues falues falues falues for risk for risk for risk for risk for risk factoractoractoractoractors #1s #1s #1s #1s #1thrthrthrthrthrough #5 beloough #5 beloough #5 beloough #5 beloough #5 belowwwww..... Risk f Risk f Risk f Risk f Risk factor vactor vactor vactor vactor values will ralues will ralues will ralues will ralues will rangangangangangeeeeefrom 1% -100%. from 1% -100%. from 1% -100%. from 1% -100%. from 1% -100%. Note: Use percent values in wholeNote: Use percent values in wholeNote: Use percent values in wholeNote: Use percent values in wholeNote: Use percent values in wholennnnnumberumberumberumberumbers not decimal pers not decimal pers not decimal pers not decimal pers not decimal percent vcent vcent vcent vcent values (i.ealues (i.ealues (i.ealues (i.ealues (i.e..... use 90% NO use 90% NO use 90% NO use 90% NO use 90% NOT 0.90).T 0.90).T 0.90).T 0.90).T 0.90).

RISK FACTOR #1: _________% +

RISK FACTOR #2: _________% +

RISK FACTOR #3: _________% +

RISK FACTOR #4: _________% +

RISK FACTOR #5: _________% =

ADD RISKFACTORS #1 - #5: ________ / 500 =

COMPOSITE RISK FACTOR =

____________

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 19

Annual Lightning Strike Probability =

lightning strike number from map X[3.142 X ((tree height in feet) X 3)2 / (5,280)2 ]

510

15

15

15

15

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2025 25

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3035

4045

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Figure 15: Risk Factor #6 --Annual Lightning Strike Probability

From map above (or using any other map source) select a lightning strikenumber per year per square mile value for your site. Insert this value into the

annual lightning strike probability formula given above.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 20

Figure 16: Tree Lightning Risk Assessment(part B & C of three calculations)

B) RB) RB) RB) RB) Recorecorecorecorecord risk fd risk fd risk fd risk fd risk factor #6,actor #6,actor #6,actor #6,actor #6, the ann the ann the ann the ann the annual lightningual lightningual lightningual lightningual lightningstrikstrikstrikstrikstrike pre pre pre pre probaobaobaobaobability belobility belobility belobility belobility belowwwww.....

RISK FACTOR #6: ANNUAL LIGHTNING STRIKE PROBABILITY =

________________

C) MultiplC) MultiplC) MultiplC) MultiplC) Multiply composite risk fy composite risk fy composite risk fy composite risk fy composite risk factor (Pactor (Pactor (Pactor (Pactor (Pararararart t t t t A) &A) &A) &A) &A) &annannannannannual lightning strikual lightning strikual lightning strikual lightning strikual lightning strike pre pre pre pre probaobaobaobaobability (Pbility (Pbility (Pbility (Pbility (Pararararart B).t B).t B).t B).t B).

COMPOSITE RISK FACTOR XANNUAL STRIKE PROBABILITY =

TOTAL TREE LIGHTNING STRIKERISK VALUE

________________ X ________________ =COMPOSITE RISK FACTOR ANNUAL LIGHTNING

STRIKE PROBABILITY

________________________TOTAL TREE LIGHTNING STRIKE RISK VALUE

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 21

CALCULATED TOTAL TREE LIGHTNING STRIKE RISK VALUE RISK DESCRIPTION

> 0.05 severe risk(installation recommended)

> 0.03 high risk> 0.02 moderate risk

(consider installation)

> 0.01 low risk< 0.005 very low risk

(no installation)

Remember that risks can be low, not zero, and lightning strikes,especially smaller current strikes, can still occur.

Figure 17: Tree Lightning Risk Assessment Response (based on calculations of risk in Part A, B, & C)

Risk description suggests whether a lightningconduction / tree protection system should be installed.

TREE LIGHTNING RISKTREE LIGHTNING RISKTREE LIGHTNING RISKTREE LIGHTNING RISKTREE LIGHTNING RISKASSESSMENT ASSESSMENT ASSESSMENT ASSESSMENT ASSESSMENT WWWWWORKSHEETORKSHEETORKSHEETORKSHEETORKSHEET

DrDrDrDrDr..... Kim D Kim D Kim D Kim D Kim D..... Coder Coder Coder Coder Coder,,,,, WWWWWarararararnell Scnell Scnell Scnell Scnell School ofhool ofhool ofhool ofhool of F F F F Forororororestrestrestrestrestry & Nay & Nay & Nay & Nay & Naturturturturtural Ral Ral Ral Ral Resouresouresouresouresourcescescescesces,,,,, Uni Uni Uni Uni Univvvvvererererersity ofsity ofsity ofsity ofsity of Geor Geor Geor Geor Georgia,gia,gia,gia,gia, No No No No Novvvvv..... 2013 2013 2013 2013 2013

RISK FACTOR #1:TOPOGRAPHIC LOCATION IN LANDSCAPE = ____________%

RISK FACTOR #2:RELATIVE TREE HEIGHT = ____________%

RISK FACTOR #3:TREE OPENNESS = ____________%

RISK FACTOR #4:RELATIVE NEIGHBORHOOD HEIGHT DIFFERENCES = ____________ %

RISK FACTOR #5:TREE TARGET PROXIMITY = ____________ %

ADD RISK FACTORS #1 - #5 TOGETHER TOTAL = ____________

DIVIDE TOTAL BY 500 = COMPOSITE RISK FACTOR = ____________

RISK FACTOR #6:ANNUAL LIGHTNING STRIKE PROBABILITY = ____________

COMPOSITE RISK FACTOR XANNUAL LIGHTNING STRIKE PROBABILITY =

TOTAL TREE LIGHTNING RISK VALUE

__________________ X ______________ = COMPOSITE RISK FACTOR ANNUAL LIGHTNING

STRIKE PROBABILITY TTTTTOOOOOTTTTTAL AL AL AL AL TREETREETREETREETREELIGHTNINGLIGHTNINGLIGHTNINGLIGHTNINGLIGHTNING

RISK RISK RISK RISK RISK VVVVVALALALALALUEUEUEUEUETTTTTOOOOOTTTTTAL AL AL AL AL TREE LIGHTNING RISK TREE LIGHTNING RISK TREE LIGHTNING RISK TREE LIGHTNING RISK TREE LIGHTNING RISK VVVVVALALALALALUEUEUEUEUE

> 0.05> 0.05> 0.05> 0.05> 0.05 sesesesesevvvvvererererere riske riske riske riske risk> 0.03> 0.03> 0.03> 0.03> 0.03 high riskhigh riskhigh riskhigh riskhigh risk> 0.02> 0.02> 0.02> 0.02> 0.02 moderate riskmoderate riskmoderate riskmoderate riskmoderate risk> 0.01> 0.01> 0.01> 0.01> 0.01 low risklow risklow risklow risklow risk< 0.005< 0.005< 0.005< 0.005< 0.005 vvvvvererererery loy loy loy loy low riskw riskw riskw riskw risk

FigurFigurFigurFigurFigure 18:e 18:e 18:e 18:e 18: Field w Field w Field w Field w Field worororororksheet.ksheet.ksheet.ksheet.ksheet.

Dr. Kim D. Coder, University of Georgia, Warnell School 2013 23

TTTTTrrrrree most likee most likee most likee most likee most likelelelelely stry stry stry stry strucucucucuck:k:k:k:k:-TR-TR-TR-TR-TRUE-UE-UE-UE-UE-

-- open g-- open g-- open g-- open g-- open grrrrrooooown or edgwn or edgwn or edgwn or edgwn or edge tre tre tre tre treeseeseeseesees-- g-- g-- g-- g-- grrrrrooooowing under drwing under drwing under drwing under drwing under dry soil conditionsy soil conditionsy soil conditionsy soil conditionsy soil conditions

(soil moisture & wet surfaces protect tree)(soil moisture & wet surfaces protect tree)(soil moisture & wet surfaces protect tree)(soil moisture & wet surfaces protect tree)(soil moisture & wet surfaces protect tree)

-F-F-F-F-FALSE-ALSE-ALSE-ALSE-ALSE--- tallest ***-- tallest ***-- tallest ***-- tallest ***-- tallest ***-- g-- g-- g-- g-- grrrrrooooowing in high rwing in high rwing in high rwing in high rwing in high resistance soilesistance soilesistance soilesistance soilesistance soil-- cer-- cer-- cer-- cer-- certain speciestain speciestain speciestain speciestain species-- c-- c-- c-- c-- close to other glose to other glose to other glose to other glose to other grrrrroundoundoundoundound

Cause ofCause ofCause ofCause ofCause of mor mor mor mor more damae damae damae damae damaggggge:e:e:e:e:-TR-TR-TR-TR-TRUE-UE-UE-UE-UE-

-- positi-- positi-- positi-- positi-- positivvvvve lightning strike lightning strike lightning strike lightning strike lightning strikeseseseses-- higher peak cur-- higher peak cur-- higher peak cur-- higher peak cur-- higher peak currrrrrententententent

-F-F-F-F-FALSE-ALSE-ALSE-ALSE-ALSE--- strik-- strik-- strik-- strik-- strikes with mores with mores with mores with mores with more stre stre stre stre strokokokokokeseseseses-- contin-- contin-- contin-- contin-- continuous curuous curuous curuous curuous currrrrrententententent

Figure 19: Field tests of traditional lightning -- tree concepts.(Makela et.al. 2009)