Trends in regional fire cycle for Alaska, 1943-2016

Thomas Paragi (ADF&G), Maija Wehmas and David Verbyla (UAF)

(draft 2--December 2019)

Abstract: Understanding of the extent and frequency of wildland fires informs protection of human infrastructure and management of renewable resources, such as wildlife habitat features. Gabriel and Tande (1983) analyzed fire cycle (years required to burn a defined area) during 1957-1979 to understand differences among defined areas of physiography (2 scales), weather forecasting, and fire management planning. Improvements in fire detection and perimeter mapping since the 1960s now permit calculation of fire regime parameters over several decades. In recent decades Alaska has experienced changes in fire regime coincident with a warming climate. We analyzed fire cycle during 1943-2016 for burns of lightning ignition over a 29-year historic period and three 17-year periods. We used the same analysis areas from the earlier study to discern trends since 1969 for areas with at least 10 fires in all three 17-year periods. We found substantial spatial variation in fire cycle and percentage area burned among smaller areas examined with apparent trends toward shorter fire cycle (more frequent burning) in the central and eastern Interior and longer fire cycle (less frequent burning) in northwest Alaska. These trends can inform periodic review of fire management options guiding initial response and spatial priority in managing hazardous fuels.

Understanding trends in fire patterns helps fire managers and fire ecologists understand the implications of a changing fire regime on management of natural resources. Fire history is the chronological record of documented fires (often of a minimum size) in a study area that incorporates fire locations, extents, frequencies, causes, and other factors (Stokes and Dieterich 1980). A previous analysis used mapped fire perimeters and other statistics acquired during 1957-1979 to describe fire history in Alaska (Gabriel and Tande 1983). That analysis focused on physiographic divisions (Wahrhaftig 1965) as spatial domains to examine geographic differences in fire history. Physiography divisions are instructive for understanding fire regime and its influence on ecology because topography has an orographic influence on weather (temperature and moisture) and lightning incidence (Dissing and Verbyla 2003, Kasischke et al. 2002), and soil parent material associated with topography and geomorphology interacts with climatic conditions to influence the vegetation (Van Cleve et al. 1991) that serves as pyrogenic fuels.

The end of the period analyzed by Gabriel and Tande (1983) approximately coincided with a climatic regime shift in 1976-77 toward warmer conditions (Hartmann and Wendler 2005). Annual fire extent and number of large fires have increased in the boreal region of North America over the last four decades (Kasischke and Turetsky 2006), particularly in Alaska (Kasischke et al. 2002). We hypothesized that the changes in climate since 1976-77 could have

1

reduced the time required for a defined area to burn (fire cycle) in recent decades but to degrees of different magnitude among the physiographic areas and fire weather zones. Johnson and Van Wagner (1985) describe the analytical basis and assumptions of estimating fire cycle.

We re-created the analytical summaries of Gabriel and Tande over a longer period (1940-2016) broken into 4 periods to examine whether changes in the regime for fires of lightning origin were evident within the same physiographic areas and within fire weather zones. Although human-caused fires are more common than lightning ignitions, we excluded human ignitions from our analysis because they compose a relatively small proportion of area burned in Alaska for most years (Table 1) and reflect a geographic bias of settlement and associated access corridors. We chose to replicate the analysis of Gabriel and Tande (1983) using physiography because it changes slowly (over geographic time scales). Thus, changes in roughly decadal fire regimes within static physiographic areas should be sensitive to changes in fire weather, natural ignition source, dynamics of pyrogenic fuels, and degrees of suppression activity. Our intent is to provide ecologists and natural resource managers addressing applied questions with a spatial context of fire regime to help interpret fire regime among geographic areas within Alaska and apparent historic trends

As we re-created the analysis of Gabriel and Tande (1983) we encountered three methodology differences that would confound comparisons between their results and our analysis: the calculated area of physiographic provinces and sections, the size and shape of fire weather zones, and the composition of fires included in the Large Fire Database following revisions (described below). We nonetheless presented our results in acres and in similar tabular listing order (geographic rather than alphabetical) as Gabriel and Tande (1983) to aid comparison with their earlier work.

Data description and analytical methods

Gabriel and Tande (1983:6) identified 4194 fires of lightning origin and 6854 fires of human

origin in Alaska from 1940-79, excluding that portion west of 141 degrees West longitude (the boundary with the Yukon) and north of an arbitrary line between the towns of Kodiak and Dillingham (Gabriel and Tande 1983:4). They measured burned area with a planimeter from plotted overlays of 3650 lightning fire boundaries during 1957-79 on a 1:2,500,000 scale map of Alaska. We validated their calculations of fire cycle in years (= area of evaluation * evaluation period [yrs] / area burned in evaluation period) within each physiographic section for this 23 year period using the areas they presented (Gabriel and Tande 1983:Table 3).

Our analysis used the Alaska Large Fire Database obtained in October 2016 from the Alaska Interagency Coordination Center1. Beginning in the late 1980s, fire records for were critically evaluated and digitized to the degree possible for fires >1000 acres (400 ha) prior to 1988 and

1 https://fire.ak.blm.gov/ .

2

>100 acres (40 ha) since 1988 (Kasischke et al. 20022). By 2016 the database included 2968 fires of lightning origin (Appendix A) as polygon records of mapped final perimeters since 1940, a substantial reduction in the number of fires compared with the number reported for 1957-1979 by Gabriel and Tande (1983:6). For comparison to the period 1957-79 analyzed by Gabriel and Tande (1983), the 2016 database contained only 492 of lightning origin (Fig. 1, Table 1), including 295 (8.5%) <100 acres (primarily since the early 2000s) as detection and mapping technology has improved. In years of high fire activity, several fires may burn into a large complex (or be tactically joined during suppression activities) that is recorded as a single fire for administrative purposes, with “complex” often part of the fire name.

We obtained shapefiles of the physiographic divisions of Alaska (Wahrhaftig 1965) from the U.S. Geological Survey in Anchorage, Alaska3. Physiographic provinces describe continental-scale mountain ranges or geological structure that are further subdivided into sections with terminology that matched that of the Canadian Cordillera so descriptions would match across the international boundary. We verified polygon boundaries against a 1:2,500,000 scale map of the physiographic sections on a hydrography background4. Wahrhaftig (1965) did not report area of physiographic boundaries, so we present GIS-calculated areas within provinces (Appendix B, Fig. 2, Table 2) and sections (Appendix C, Fig. 3, Table 3). Gabriel and Tande (1983:Fig. 10) also analyzed fire statistics for fire planning regions (Fig. 4) and fire weather zones. The latter boundaries have changed, so we obtained the current fire weather zones used by the U.S. National Weather Service (Appendices D and E; Fig. 5).

Fire regime calculations assume a complete record of fire history. Gabriel and Tande (1983) described challenges in interpreting the earlier years of Alaska fire data due to in administrative changes in reporting and inconsistent use of terminology. Kasischke et al. (2002:137) noted limitations of the Alaska Large Fire Database prior to 1971 because of missing records (e.g., maps describing an estimated 15% of the total area are missing since 1950) but described it as a “reasonable sample of fire activity” for analysis of fire cycle “in a relative sense.” Beginning in the early 1970s, fire data were acquired from more organized surveillance, mapping, and lightning detection (Jewkes and Todd 2006:37). Even today, smaller fires tend to have lower detection probability from aircraft and may be underrepresented, particularly in remote areas (DeWilde and Chapin 2006).

To analyze change in lightning fires over time, we defined three 17-year intervals over the period during which fire detection and spatial archive were reasonably comparable (1969-1985, 1985-2000, and 2001-2016). Excluding the few records of 1940-42 (Appendix A), we also included a unique 26-year period (1943-1968) for comparison to statistics reported in Gabriel and Tande (1983). However, we urge caution in drawing inference from Alaska fire data prior to 1969

2 Incorrectly described the latter size as 63 acres (25 ha) (Kasasischke et al. 2002:133).3 Province and section feature classes provided courtesy of Nora Shew, U.S. Geological Survey, Anchorage, Alaska, 11 April 2016.4 https://pubs.er.usgs.gov/publication/pp482 (accessed 31 December 2019).

3

because fire detection and mapping resolution was probably lower, especially earlier in the period. We present sample size of fires used to calculate statistics by physiographic province and section, fire weather zone, and planning area to allow readers to gauge data sufficiency for fire cycle. Most fires have occurred in the central and eastern portion of the state between the Brooks Range and Alaska Range (Fig. 6), so we expect the calculated statistics for Interior Alaska to be the best representation of fire activity. We inferred trend in fire cycle only for geographic areas having >10 fires within a period for the three 17-year periods covering 1969-2016.

To calculate area burned for within periods, we intersected the shapefile records of fire perimeters and the boundaries of spatial domains (physiographic province or section, fire weather zone, and fire planning region) in ArcGIS 10.3 (ESRI, Inc.). Some fires extended over domain boundaries, and a few fires extended over multiple boundaries, so burned area was partitioned accordingly. Percentage burned by period was calculated by adding the area of all fires during respective analysis periods (including area re-burned when >2 burns overlap) within respective boundaries and dividing the sum by the total area. ArcGIS feature classes with fire cycle calculations for the 4 periods and 4 spatial domains are archived with Python code in a separate attachment at https://www.frames.gov/catalog/60487.

Evaluation of wildland fire regime must consider the potential effectiveness of fire suppression activity. Fire suppression in Alaska became organized in the 1940s and since the 1980s has been zoned by option for response by land managers (Fig. 7) according to planning based on resources at risk balanced against the ecological role of fire in renewable resource management (Jewkes and Todd 2006, Alaska Wildland Fire Coordinating Group 2016). Suppression activity can reduce fire extent in areas zoned for immediate suppression to protect human resources (DeWilde and Chapin 2006), but substantial portions of Alaska are in Limited and do not receive initial attack actions typical for Critical, Full, and Modified (treated as Full prior to an annual conversion date to Limited, often in early July). Fire management options are subject to change annually, but we used 2016 options to provide a gross characterization of regional differences after several regional plans were consolidated in the 1980s into a set of interagency plans that spanned the state (Alaska Wildland Fire Coordinating Group 2016). We calculated the proportion of each fire management option in 2016 within physiographic provinces to provide a context for potential suppression activity that might have affected area burned by lightning fires during the study period. A detailed analysis of actual suppression activity by fire each year, where decisions are based on triage given available resources and other public and landowner considerations, was beyond the scope of our analysis.

Results

Lightning-caused fires used in our analysis averaged annually 80% of all fires and 82% of area burned since 1969 (Table 1). Revisions to the Large Fire Database greatly reduced earlier tallies of number of fire in some years during 1957-1979 (Fig. 1a) but not substantively the area burned

4

(Fig. 1b). Human-caused fires were the predominant area burned only in years of relatively low fire extent statewide (Fig. 1b). Most of the physiographic provinces were predominantly the Limited option for suppression in 2016 (Fig. 8), with exceptions being the Seward Peninsula (60% in Modified with typically a late summer conversion date, thus essentially Full) and Bering Shelf (50% in Full).

A few substantially large fires can give strong positive bias to mean size in physiographic provinces (Fig. 9). For example, during 1943-1968, central tendency in the Bering Shelf province was skewed by the 354,350-acre Paimiut fire in 1954 (1 of 5 fires), and Seward Peninsula was skewed by the 415,050-acre Imuruk Basin fire in 1954 (1 of 8 fires). This illustrates the effect of single large fires on scale of total area burned in fire cycle calculations when few burns occur in a period. Where mean fire size was generally <30,000 acres there were no substantive trends in percentage of province burned among periods despite positive or negative trends in fire size (Fig. 9). For the three provinces with mean fire size exceeding 50,000 acres in at least one 17-year period since 1969, the Seward Peninsula had a declining trend in fire size and percentage of province burned, Western Alaska had a declining mean size but increased percentage burned since 2001, and Northern Plateaus had a steady size of fires but dramatically increased percentage burned since 1969 (Fig. 9).

Fire planning regions were the largest spatial domains we analyzed for fire cycle, which became shorter in the Southwest and Yukon regions since 1969 (Table 1). We found a mixed trend in the Northwest region despite a substantial lengthening of fire cycle from the first period to the latter two periods (Table 1).

The size distribution of physiographic provinces was skewed toward Northern Plateaus and Southwest (Fig. 2), resulting in a dominance in number of fires and area burned for calculation of fire cycle (Fig. 6). For provinces closer to coastal environments, trend in fire cycle seemed consistent since 1969 in the Arctic Mountains but to have dramatically shortened since 2001 on the Bering Shelf (Fig. 10) and lengthened since 1969 on the Seward Peninsula (Fig. 11). Fire cycle has generally shortened for Northern Plateaus and Western Alaska (Fig. 11).

Number of fires and area burned in physiographic provinces (Table 2) are larger than in physiographic sections (Table 3) because provinces are composed in most instances by >1 section. For 7 sections with fire cycle exceeding 500 years in at least one 17-year period since 1969, the Seward Peninsula had the unique pattern of lengthened fire cycle, whereas 15 sections had shortened fire cycle, either a consistent trend since 1969 or just since 2001 (Fig. 12). For the 22 sections with fire cycle <50 years in at least one period since 1969, sections within the boreal forest of central and eastern Alaska generally have shortened fire cycle, whereas sections in western and northern fringes of boreal forest generally have lengthened fire cycle (Fig. 13).

5

Fire weather zones were smaller scale than fire planning regions but more equitably sized than physiographic provinces, resulting in smaller numbers of burns and area burned (Table 4). Most fire weather zones with the longest historic fire cycles (>4000 years) tended to decrease substantially from the second to third period (Fig. 14). The general pattern seen for physiographic provinces of shorter cycle in central and eastern Alaska and longer cycle in western and northern Alaska (Table 4) was also observed for intermediate cycles (200-800 years; Fig. 15) and shorter cycles (50 years; Fig. 16) in fire weather zones. However, partitioning the fires into many smaller spatial domains increases potential for smaller number of fires to affect fire cycle calculations, resulting in more mixed trends among periods (Table 4) than in physiographic provinces (Table 2).

Discussion

Attention to number of fires in a period is warranted when interpreting our results, particularly at the smaller geographic scale of physiographic sections. Increasing trend in total number of fires within the periods we defined can be discerned from all the spatial domains we examined. Physiographic provinces seem to be a practical scale for illustrating trend in fire cycle based on clustering a sufficiently large number of burns. If fire cycle is of interest in fire management planning, better awareness of this domain might be useful in the context of land ownership and fire protection zoning.

Other geographic boundaries may be useful scales for understanding fire history in different contexts. Kasischke et al. (2002) used an earlier version of the Large Fire Database to calculate fire history over 1950-1999 for 20 ecological regions of Alaska (Gallant et al. 1995) prior to analyzing statistical correlation of regional fire cycle to climatic and vegetative variables. Use of vegetation type can eliminate areas with little or no pyrogenic fuels (e.g., above treeline), thus correcting area for fire cycle calculations. Suppression agencies might find the fire management zones that serve as administrative boundaries to be instructive regions for calculating fire cycle to examine historic correlation in fire occurrence and associated degree of suppression response.

For a defined area, a relatively constant burned area over time suggests fire extent is driven largely by topography and orographic weather, whereas changes in burned area over time suggests area burned is driven by changes in ignition frequency and distribution, climate (fire weather conditions ), or post-fire succession of vegetative fuels (potential for fire ignitions to spread). A change in fire regime over time is expected when there are changes in climate, ignition source, or vegetation (e.g., Larsen 1997). Johnson et al. (1998) argued there is not a single “natural” fire cycle but that the forested boreal landscape reflects a dynamic fire cycle over longer periods (200-300 years). Our exploratory analysis using deterministic calculations of fire cycle was over relatively short periods but is still a gross characterization of a complex fuel environment, annual variation in weather, climate trajectory, and myriad factors affecting suppression activities on lightning fires in a given year (e.g., resources allocated on suppressing human-caused fires in Critical or Full vs. lightning fires in Limited). The qualification of

6

“relative fire cycle” (Kasischke et al. 2002) seems prudent when earlier data were of coarser mapping resolution so readers take appropriate caution in drawing inference on geographic trend.

Physiographic sections with >10 lightning fires in the periods since 1969 often had shortened fire cycle in the central and eastern portions of the boreal forest in the Interior and lengthened fire cycle in the western and northern portions of sparse forest and shrub tundra. Exceptions of shorter fire cycle in portions of northern and western Alaska, such as the Bering Shelf province, might reflect an increase in pyrogenic shrubs such as Betula as observed elsewhere in Alaska (Sturm et al. 2001) or increased frequency of drought during fire season. an.

As burned area in Alaska has increased in recent decades (Kasiscke et al. 2002), two phenomena may be occurring. First, as fire size increases in boreal forest, the proportion of unburned inclusions within perimeters tends to increase because larger fires tend to burn over multiple fuel types and over longer periods during which changes in weather affect fire behavior (Eberhardt and Woodard 1987, DeLong and Tanner 1996). The Large Fire Database presently does not subtract area of unburned inclusions from area within mapped perimeters, so it represents the maximum extent of fire and to a degree a positive bias in actual area burned. The increased availability of historical estimates of fire severity for larger burns5 may allow mapping of unburned inclusions for corrected estimates of area burned. Better understanding of the configuration of burn perimeters and unburned inclusions will also inform inference in how spatial patterns in vegetation affected by fire and other landscape features that influence suitability as wildlife habitat (Hunter 1990, Bissonette 1997). Second, re-burning of recent burns seems to be increasing (J. Barnes, National Park Service, Fairbanks, Alaska, pers. comm.). We did not analyze extent of re-burning solely based on burn perimeters because of limited resolution and lack of data on unburned inclusions. This phenomenon may also be best addressed with validating finer resolution of perimeters and unburned inclusions.

Apparent trends in fire cycle since 1969 should not be considered as predictive of future trends. Forecasting probability of future fire regime first requires knowledge of historic area burned as a coupling between vegetative dynamics (fuel types) and appropriate climatic drivers (Rupp et al. 2007). Forecasts of future fire regime for Alaska have used state-change models that incorporate potential climatic conditions and potential for fire to spread among vegetation types (Rupp and Mann 2005). Research is improving the understanding of fire spread to modify assumptions that should improve model performance (e.g., Wehmas 2018).

Fire cycle is one factor to consider when attempting to achieve or maintain a “natural” disturbance regime in boreal forest using practices such as logging, prescribed fire, and suppression policy in specific areas. However, Johnson et al. (1996) noted that defining fire regime requires assumptions including fire frequency, flammability of accumulated fuels and the resulting burn mosaic (perimeter and unburned inclusions). They stressed the need to understand

5 Monitoring trends in burn severity (www.mtbs.gov)

7

the dominant role of large fires in landscape vegetation patterns and using appropriate scales of area and time to define fire regime.

Literature Cited

Alaska Wildland Fire Coordinating Group. 2016. Alaska Interagency Wildland Fire Management Plan 2016. <link> (accessed 8 March 2017)

Bissonette, J. A., editor. 1997. Wildlife and landscape ecology: Effects of pattern and scale. Springer, New York.

DeLong, S., and D. Tanner. 1996. Managing the pattern of forest harvest: lessons from wildfire. Biodiversity Conservation 5:1191–1205.

DeWilde, L., and F.S. Chapin III. 2006. Human impacts on the fire regime of Interior Alaska: interactions among fuels, ignition sources, and fire suppression. Ecosystems 9:1342-1353.

Dissing D., and D. Verbyla. 2003. Spatial patterns of lightning strikes in interior Alaska and their relations to elevation and vegetation. Canadian Journal of Forest Research 33:770–782.

Eberhardt, K.E., and P.M. Woodard. 1987. Distribution of residual vegetation associated with large fires in Alberta. Canadian Journal of Forest Research 17:1207-1212..., 17, 1207-12.

Gabriel, H.W., and G.F. Tande. 1983. A regional approach to fire history in Alaska. U.S. Department of the Interior, Bureau of Land Management, Alaska Technical Report BLM/AK/TR-83/09. 34 p.

Gallant, A.L, E.F. Binnian, J.M. Omernik, and M.B. Shasby. 1995. Ecoregions of Alaska. U.S. Geological Survey Professional Paper 1567. 73 p.+ map.

Hartmann, B., and G. Wendler. 2005. The significance of the 1976 Pacific climate shift in the climatology of Alaska. Journal of Climate 18:4824–4839.

Hunter, M. L., Jr. 1990. Wildlife, forests, and forestry: Principles for managing forests for biological diversity. Prentice-Hall, Englewood Cliffs, New Jersey.

Johnson, E.A., K. Miyanishi, and J.M.H. Weir. 1998. Wildfires in western Canadian boreal forest: landscape patterns and ecosystem management. Journal of Vegetation Science 9:603-610.

Johnson, E.A., and C.E. Van Wagner. 1985. The theory and use of two fire history models. Canadian Journal of Forest Research 15:214-220.

Kasischke, E.S., and M.R. Turetsky. 2006. Recent changes in the fire regime across the North American boreal region—Spatial and temporal patterns of burning across Canada andAlaska. Geophysical Research Letters Vol. 33 (doi:10.1029/2006GL025677)

Kasischke, E.S., D. Williams, and D. Barry. 2002. Analysis of the patterns of large fires in the boreal forest region of Alaska. International Journal of Wildland Fire 11:131-144.

8

Larsen, C.P.S. 1997. Spatial and temporal variations in boreal forest fire frequency in northern Alberta. Journal of Biogeography 24:663-673.

Mann, D. H., T. S. Rupp, M. A. Olson, and P. A. Duffy. 2012. Is Alaska’s boreal forest now crossing a major ecological threshold? Arctic, Antarctic, and Alpine Research 44(3):319-331. http://doi. org/10.1657/1938-4246-44.3.319

Partain, J.L., Jr., S. Alden, U.S. Bhatt, P.A. Bienie,, B.R. Brettschneider, R.T. Lader, P.Q. Olsson, T.S. Rupp, H. Strader, R.L. Thoman, Jr., J.E. Walsh, A.D. York, and R.H. Ziel. 2016. An assessment of the role of anthropogenic climate change in the Alaska fire season of 2015. Bulletin of the American Meteorological Society 97(12):S14-S18.

Rupp, T.S., X. Chen, M. Olson, and A.D. McGuire. 2007. Sensitivity of simulated boreal fire dynamics to uncertainties in climate drivers. Earth Interactions 11(3):1-21.

Rupp, T. S., P. Duffy, M. Leonawicz, M. Lindgren, A. Breen, T. Kurkowski, A. Floyd, A. Bennett, and L. Krutikov. 2016. Climate simulations, land cover, and wildfire in Alaska. Pages 17-52 in Z. Zhu and A. D. McGuire, editors. Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of Alaska. Professional Paper 1826. U.S. Geological Survey, Reston, Virginia, USA.

Rupp, T.S., and D.H. Mann. 2005. Development of a computer model for management of fuels, human-fire interactions, and wildland fires in the boreal forest of Alaska. Final report to the Joint Fire Sciences Program. JFSP Project No. 01-1-1-02. University of Alaska, Fairbanks. 17 p.

Stokes, M.A., and J.H. Dieterich, technical coordinators. 1980. Proceedings of the fire history workshop, October 20-24, 1980, Tucson, Arizona. General Technical Report RM-81. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado.

Sturm, M., C. Racine, and K. Tape. 2001. Climate change: Increasing shrub abundance in the Arctic. Nature 411:546-547.

Todd, S.K, and H.A. Jewkes. 2006. Wildland fire in Alaska: a history of organized fire suppression and management in the last frontier. Agricultural and Forestry Experiment Station Bulletin No. 114, University of Alaska Fairbanks. 64 p.

Van Cleve, K., F. S. Chapin III, C. T. Dyrness, and L. A Viereck. 1991. Element cycling in taiga forests: state factor control. BioScience 41:78-88.

Wahrhaftig, C. 1965. Physiographic divisions of Alaska. U.S. Geological Survey Professional Paper 482. 52 p. + map.

Wehmas, M.I. 2018. Temporal and spatial variation of broadleaf forest flammability in boreal Alaska. M.S. Thesis, University of Alaska, Fairbanks.

9

a

1940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

2014

2016

0

50

100

150

200

250

300

350

400

450

500

Gabriel and Tande 1983

Present analysis

Num

ber o

f lig

htni

ng-o

rigin

fire

s

10

b

Figure 1. Number of lightning-origin fires (a) and area burned (b) for Alaska during 1940-2016. The period 1957-1979 is shown from earlier analysis (Gabriel and Tande 1983). Asterisks indicate years since 1950 when area burned by human-caused fires exceeded area of lightning-caused fires for the present analysis (human-caused 53-100% by area; see Table 1).

11

Fig. 2. Physiographic provinces of Alaska (Wahrhaftig 1965) with lightning fires, 1940-2016.

12

Figure 3. Physiographic sections of Alaska (Wahrhaftig 1965) with lightning fires, 1940-2016. Section names are identified by number in Appendix C.

13

Figure 4. Fire planning regions with lightning fires, 1940-2016.

14

Figure 5. Fire weather zones in Alaska (U.S. National Weather Service) with lightning fires, 1940-2016. Zone names are identified by number in Appendix D.

15

Figure 6. Perimeters of 2968 lightning-caused fires and 504 human-caused fires in Alaska, 1940-2016. Most fires occurred between the Brooks Range on the north and the Alaska Range on the south, with an exception being several human-caused fires on the northern Kenai Peninsula.

16

HU

Figure 7. Fire management options for potential suppression actions on wildland fires during the 2016 season in Alaska.

17

Arctic C

oastal

Plain

Arctic F

oothills

Arctic M

ountains

Northern

Plateau

s

Western

Alaska

Seward

Peninsula

Bering S

helf

Akhlum M

ountains

Alaska

-Aleutian

Coastal T

rough

Pacific B

order

Range

s0

0.2

0.4

0.6

0.8

1

Critical

Full

Modified

Limited

Figure 8. Proportions of physiographic provinces by fire management options, 2016, Alaska.

18

a

Alaska-Aleutian

Arctic Foothills

Arctic Mountains

Bering Shelf

Coastal Trough

Northern Plateaus

Pacific Border Ranges

Seward Peninsula

Western Alaska

0

10,000

20,000

30,000

40,0001943-19681969-19841985-20002001-2016

Mea

n fir

e siz

e (a

c)

b

Alaska-Aleutian

Arctic Foothills

Arctic Mountains

Bering Shelf

Coastal Trough

Northern Plateaus

Pacific Border Ranges

Seward Peninsula

Western Alaska

0

2,000

4,000

6,000

8,0001943-19681969-19841985-20002001-2016

Med

ian

fire

size

(acr

es)

Figure 9. Mean (a) and median (b) fire size by physiographic province in Alaska with >10 fires per period, 1943-2016.

19

Arctic Foothills Arctic Mountains Bering Shelf Alaska-Aleutian Coastal Trough Pacific Border Ranges

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

16

221 87 77

28

16

18

90

29

69

26

35

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 10. Physiographic provinces in Alaska with comparatively long fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

20

Seward Peninsula Northern Plataeus Western Alaska0

200

400

600

800

1,000

1,200

8

330 62043 213 690

17

847 1125

30

1176 1983

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 11. Physiographic provinces in Alaska with comparatively short fire cycles during four periods, 1943-2016. Number of fires is shown above bars.

21

Centra

l East

ern Bro

oks Ran

ge

Nowitna L

owland

Nulato Hills

Nushagak-

Big Rive

r Hills

Seward

Peninsula

Yuko

n-Kuskokw

im Coast

al

Yuko

n-Tanan

a Uplan

d0

500

1000

1500

2000

2500

3000

3500

23

12

61

10

49

29

28

27

63

58

4025

26

278

59

145121 72

36

87

36921

3696

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 12. Physiographic sections in Alaska with comparatively long fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

22

Ambler-Chan

dalar

Indian Rive

r Uplan

d

Innoko Lo

wlands

Kanuti Fla

ts

Kobuk-Sela

wik Lowlan

d

Kokrine-H

odzana H

ighlan

ds

Koyuku

k Flat

s

Kuskokw

im M

ountains

Noatak L

owlands

Ogilvie

Mountains

Pah Rive

r Secti

on

Porcupine P

latea

u

Tanan

a-Kusko

kwim

Lowlan

d

Tozitn

a-Melo

zitna L

owland

Yuko

n Flats

Section

0

50

100

150

200

250

300

1493

26 24

21

96 91

244

21

58

73

36118

21

111

29

31

70

78 91

457

4116

67

45

106

60

75

27

105 2945

37

17069

16

14

6974

163324

53 274

68

16058

52

65

304 150 838

89

121

72

219 397 88 362

1940-19681969-19841985-20002001-2016

Fire

cycle

(yea

rs)

Figure 13. Physiographic sections in Alaska with comparatively short fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

23

Copper River Basin

Eastern Norton Sound- Nulato

Hills

Greater Bristol Bay

Kuskokwim Delta Western Alaska Range

Yukon Delta0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

25

33 16 5534

2214 29

10

1022

13

15

13

10

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 14. Fire weather zones in Alaska with comparatively long fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

24

Deltan

a and Ta

nana F

lats

Denali

Lower Kobuk a

nd Noatak V

alleys

Middle Kusko

kwim

Valley

Middle Tan

ana V

alley

North. -

Interior S

eward

Peninsula

Southea

stern Bro

oks Ran

ge

Upper Kobuk a

nd Noatak V

alley

s

Upper Tan

ana V

alley

- Forty

mile 0

100

200

300

400

500

600

700

800

17

33

21

99

39

28

49

61

213

3767

69

152

74

51

94

151

297

37

21

12

74

30

105

30

3323

16 27

20

62

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 15. Fire weather zones in Alaska with intermediate duration fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

25

0

50

100

150

200

250

300

350

400

15 125 165

79

154

39

107150

226 95 125

28

167305 302 129200

132

468635516 227

326205

575

1940-1968

1969-1984

1985-2000

2001-2016

Fire

cycle

(yea

rs)

Figure 16. Fire weather zones in Alaska with comparatively short fire cycles during four periods, 1943-2016. Number of fires is shown above bars (periods with <10 fires lack bars).

26

Table 1. Fire cycle by fire planning region where lightning fires occurred during four periods, 1943-2016, Alaska. Dash indicates no fires in period; calculations only for >10 fires.

Planning region

Square miles

1943-1968 1969-1984 1985-2000 2000-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burned

No. fires

Fire cycle

% burned

No. fires

Fire cycle

% burned

No. fires

Fire cycle

% burned

Arctic 84,258 -- 2 3 15 3,139 1 --

Northwest 68,117 20 1,215 2 170 288 6 100 1,109 2 271 962 2 mixedSouthcentral 83,570 3 1 5 37 5,865 0.3 --Southwest 210,063 41 4,761 1 48 3,248 1 172 1,059 2 324 937 2 shorterYukon 204,176 265 372 7 246 436 4 872 228 7 1559 101 17 shorter

Total 326 464 1144 2206Avg./yr. 13 27 67 130

27

Table 2. Fire cycle by physiographic province where lightning fires occurred during four periods, 1943-2016, Alaska. Dash indicates no fires in period; calculations only for >10 fires.

Physiographic provinces

1943-1968 1969-1984 1985-2000 2000-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Arctic Coastal Plain -- 1 -- 5 --Arctic Foothills -- 2 5 16 1,796 1 --Arctic Mountains 8 64 1,134 1 50 2,262 1 190 1,070 2 mixedNorthern Plataeus 112 417 6 63 621 3 439 149 11 644 75 23 shorterWestern Alaska 204 426 6 300 364 5 609 311 5 1186 155 11 shorterSeward Peninsula 2 28 211 8 12 1,294 1 23 2,689 1 longerBering Shelf 4 23 3,373 1 21 5,422 0.3 77 660 3 mixedAhklum Mountains -- -- 6 4 --Alaska-Aleutian 6 5 27 2,126 1 65 1,180 1 --Coastal Trough 3 1 3 27 3,869 0.4 --Pacific Border Ranges 1 -- 2 16 12,713 0.1 --

Totals 340 487 1174 2253

28

Table 3. Fire cycle by physiographic section where lightning fires occurred during four periods6, 1943-2016, Alaska. Dash indicates no fires in period; calculations only for >10 fires.

Physiographic section

1943-1968 1969-1984 1985-2000 2001-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Arctic Coastal Plain --Arctic Foothills -- 2 5 16 1,796 1 --DeLong Mountains -- 11 2,837 1 -- 7 --Noatak Lowlands -- 30 200 9 9 72 257 7 --Baird Mountains 1 13 1,720 1 6 22 2,843 1 --Central and Eastern Brooks Range 3 14 7,352 0.2 22 10,674 51 4,819 0.4 mixed

Ambler-Chandalar Ridge and Lowland 6 12 210 8 19 393 4 57 161 1 mixed

Porcupine Plateau 17 890 3 12 1,424 1 77 140 12 124 120 14 shorterOgilvie Mountains 11 360 7 5 33 125 14 70 56 30 --Tintina Valley 3 -- 2 14 96 18 --Yukon-Tanana Upland 39 595 4 9 168 288 6 192 80 21 --Northway-Tanacross Lowland 5 1 12 256 7 21 149 11 --

Yukon Flats 31 221 12 23 339 5 110 86 20 140 61 28 shorterRampart Trough 2 -- 15 80 21 11 73 23 --Kokrine-Hodzana Highlands 26 279 9 22 258 7 82 133 13 159 52 33 shorter

Kanuti Flats 9 12 74 23 21 76 22 23 54 31 mixedTozitna-Melozitna Lowland 6 11 40 43 26 74 23 36 31 55 mixed

Table 3 (continued)

6 No fires occurred in the following sections: Ahklun Mountains, Alaska Range (central and eastern part), Alaska Range (southern part), Aleutian Islands, Aleutian Range, Arctic Coastal Plain, Bering Platform, Boundary Ranges, Broad Pass Depression, Chatam Trough, Chilkat-Baranof Mountains, Clearwater Mts, Coastal Foothills, Cook Inlet-Susitna Lowland, Duke Depression, Gulf of Alaska Coastal, Gulkana Upland, Kodiak Mountains, Kupreanof Lowland, Nushagak-Bristol Bay Lowland, Old Crow Plain, Prince of Wales Mountains, St. Elias Mountains, Talkeetna Mountains, Upper Mantanuska Valley, Wrangell Mountains.

29

Physiographic sections

1943-1968 1969-1984 1985-2000 2001-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Indian River Upland 28 365 7 35 66 26 51 185 9 79 68 25 mixedPah River 2 29 124 14 48 177 10 51 245 7 longerKoyukuk Flats 30 158 16 28 99 17 27 287 6 77 103 17Kobuk-Selawik Lowland 10 585 4 49 194 9 24 296 6 50 522 3

Selawik Hills 1 11 104 16 2 1Buckland River Lowland -- 14 218 8 2 11 405 4 --

Nulato Hills 20 193 13 42 689 2 48 2,905 1 89 383 4 mixedTanana-Kuskokwim Lowland 20 982 3 25 223 8 91 167 10 215 76 22 shorter

Nowitna Lowland 8 4 19 128 13 73 37 46 --Kuskokwim Mountains 79 273 10 67 749 2 244 153 11 484 88 19 shorterInnoko Lowlands 14 235 11 18 697 2 18 226 8 40 174 10 shorterNushagak-Big River Hills 9 10 4,079 0.4 32 736 2 59 250 7 shorter

Holitna Lowland 5 2 4 24 771 2 --Nushagak-Bristol Bay Lowland 4 1 8 8

Seward Peninsula 2 28 211 8 12 1,294 1 23 2,689 1 longerYukon-Kuskokwim Coastal Lowland 4 23 3,373 1 21 5,422 77 660 3 mixed

Ahklun Mountains -- -- 6 4Alaska Range South -- 1 1 3Central and East Alaska Range -- -- 1 8

Northern Foothills, Alaska Range 1 3 14 793 2 37 364 5 --

Gulkana Upland 1 -- -- 7

30

Table 3 (continued)

Physiographic sections1943-1968 1969-1984 1985-2000 2001-2016 Trend in fire

cycle1969-2016No.

firesFire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Copper River Lowland 3 1 3 11 1,180 1 --Wrangell Mountains -- 1 -- 1 --Kenai-Chugach Mountains 1 -- 2 16 4,837 0.4 --

Totals 401 569 1285 2463

31

Table 4. Fire cycle and percentage of fire weather zones burned by lightning fires during four periods7, 1943-2016, Alaska. Dash indicates no fires in period; calculations only for >10 fires.

Fire weather zone

1943-1968 1969-1984 1985-2000 2000-2016Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Baldwin Peninsula and Selawik Valley 1 13 186 9 1 3

Central Beaufort Sea Coast -- -- -- 2

Central Interior 39 406 6 28 226 8 131 155 11 337 48 35 shorter

Chukchi Sea Coast -- 2 -- 4

Copper River Basin 3 -- 1 4 -- 24 3,849 --Deltana and Tanana Flats 3 3 16 579 35 129 0.4 --

Denali 2 2 28 1,744 3 61 460 13 --Eastern Alaska Range 4 2 8 1 10 1,837 4 --

Eastern Norton Sound and Nulato Hills

9 20 547 24 6,724 24 926 1 mixed

Glacier Bay -- -- -- 2 --

Greater Bristol Bay 6 2 13 8,248 0.2 15 8,127 0.2 --

Kuskokwim Delta 1 7 11 16,900 0.1 50 902 2 --Lower Kobuk and Noatak Valleys 2 32 575 3 15 1,012 2 60 943 2 mixed

Lower Koyukuk and Middle Yukon Valleys

77 195 13 59 216 8 157 206 8 302 103 17 mixed

7 No fires occurred in the following fire weather zones: Alaska Peninsula, Anchorage, Cape Decision to Salisbury Sound Coastal Area, Cape Fairweather to Cape Suckling Coastal Area, Central Aleutians, Dixon Entrance to Cape Decision Coastal Area, Dixon Entrance to Cape Decision Coastal Area, Eastern Aleutians, Eastern Baranof Island and Southern Admiralty Island, Eastern Beaufort Sea Coast, Eastern Chichagof Island, Glacier Bay, Haines Borough and Lynn Canal, Inner Channels from Kupreanof Island to Etolin Island, Juneau Borough and Northern Admiralty Island, Kodiak Island, Matanuska Valley, Misty Fjords, Northeast Prince William Sound, Northern Arctic Coast, Pribilof Islands, Salisbury Sound to Cape Fairweather Coastal Area, Southeast Prince William Sound, Southern Inner Channels, St Lawrence Island and Bering Strait Coast, Taiya Inlet and Klondike Highway, Western Aleutians, Western Arctic Coast.

32

Table 4 (continued)

Fire weather zone

1943-1968 1969-1984 1985-2000 2000-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Lower Yukon Valley 31 124 21 41 730 2 66 387 4 120 119 14 shorter

Middle Kuskokwim Valley 22 777 3 14 1,266 1 68 162 10 118 209 8 mixed

Middle Tanana Valley 12 451 6 5 24 605 3 43 75 23 --

Northeastern Brooks Range 6

Northern and Interior Seward Peninsula

4 55 149 11 20 1,035 2 40 975 2 mixed

Northwestern Brooks Range -- 2 3 8

Southeastern Brooks Range 9 15 2,470 0.1 33 1,505 1 72 479 4 shorter

Southern Seward Peninsula Coast -- -- -- 1

Susitna Valley 3Upper Kobuk and Noatak Valleys 1 60 293 6 47 623 3 133 786 2 longer

Upper Koyukuk Valley 31 241 11 46 111 15 104 121 11 169 57 30 mixed

Upper Kuskokwim Valley 12 1,190 2 18 256 7 74 147 9 136 116 15 shorter

Upper Tanana Valley and the Fortymile Country

34 628 4 10 1,376 1 129 314 11.2 176 77 22 shorter

Western Alaska Range 1 8 10 4,400 0.2 30 1,060 2 --

Western Kenai Peninsula -- -- -- -- 10 934 2 --

Western Prince William Sound -- -- 1 --

33

Table 4 (continued)

Fire weather zone

1943-1968 1969-1984 1985-2000 2000-2016 Trend in fire cycle

1969-2016No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

No. fires

Fire cycle

% burn

Yukon Delta 2 9 10 9,108 0.2 21 1,039 2 --Yukon Flats and Surrounding Uplands

46 347 8 33 485 4 222 85 20 298 64 26 shorter

Total 352 487 1219 2311

34

Appendix A. Number of fires and area burned by year and by ignition source in Alaska, 1940-2016.

Lightning-caused fires Human-caused fires All firesAcres burned Acres burned Acres burned

Year No.% all fires

Avg. per fire

Total per year

% all

acres No.

% all

firesAvg.

per fireTotal per

year

% all

acres No.

Avg. per fire

Total per year

1940 0 1 100 12,865 12,865 100 1 12,865 12,8651941 0 0 01942 0 5 100 5,693 28,465 100 5 5,693 28,4651943 1 13 121,201 121,201 50 7 88 17,485 122,398 50 8 30,450 243,5991944 1 100 96,142 96,142 100 0 0 0 0 1 96,142 96,1421945 0 0 01946 11 92 34,887 383,753 99 1 8 4,007 4,007 1 12 32,313 387,7601947 3 60 8,596 25,788 7 2 40 159,537 319,074 93 5 68,972 344,8621948 1 25 14,069 14,069 40 3 75 6,897 20,692 60 4 8,690 34,7611949 0 0 01950 14 41 56,610 792,533 25 20 59 116,551 2,331,013 75 34 91,869 3,123,5461951 3 25 13,547 40,641 14 9 75 28,284 254,557 86 12 24,600 295,1971952 1 100 2,690 2,690 100 0         1 2,690 2,6901953 11 65 32,331 355,643 75 6 35 19,402 116,411 25 17 27,768 472,0541954 19 95 91,459 1,737,726 99 1 5 18,055 18,055 1 20 87,789 1,755,7801955 2 40 1,903 3,806 22 3 60 4,462 13,387 78 5 3,439 17,1931956 8 80 57,156 457,251 96 2 20 10,097 20,195 4 10 47,745 477,4461957 59 89 79,375 4,683,108 96 7 11 25,670 179,687 4 66 73,679 4,862,7951958 14 67 18,194 254,716 76 7 33 11,219 78,536 24 21 15,869 333,2521959 37 84 13,411 496,206 89 7 16 8,552 59,863 11 44 12,638 556,0701960 1 33 6,388 6,388 13 2 67 22,036 44,072 87 3 16,820 50,4591961 0 0 01962 7 100 2,562 17,932 100 0       7 2,562 17,9321963 3 75 3,103 9,309 100 1 25 196 196 2 4 2,327 9,3091964 0 0 01965 1 100 1,281 1,281 100 0       1 1,281 1,2811966 7 78 101,372 709,607 100 2 22 27,359 54,718 8 9 78,845 709,6071967 0       14 100 6,902 96,631 100 14 6,902 96,6311968 50 98 15,424 771,214 99 1 2 5,512 5,512 1 51 15,230 776,7261969 32 63 71,980 2,303,351 53 19 37 106,225 2,018,271 47 51 84,738 4,321,623

35

1970 13 87 6,479 84,222 96 2 13 1,736 3,471 4 15 5,846 87,693

36

Appendix A (continued)

Lightning-caused fires Human-caused fires All firesAcres burned Acres burned Acres burned

Year No.% all fires

Avg. per fire

Total per year

% all

acres No.

% all

firesAvg.

per fireTotal per

year

% all

acres No.

Avg. per fire

Total per year

1971 53 95 18,148 961,830 99 3 5 2,593 7,780 1 56 17,314 969,6101972 115 100 8,157 938,101 99 0       115 8,238 947,4271973 6 75 9,108 54,647 100 2 25 4,663 9,326 17 8 6,831 54,6471974 26 87 18,942 492,491 97 4 13 4,279 17,114 3 30 16,987 509,6061975 3 50 26,471 79,413 67 3 50 13,290 39,871 33 6 19,881 119,2841976 6 60 7,837 47,020 70 4 40 5,030 20,121 30 10 6,714 67,1411977 42 95 55,268 2,321,267 100 2 5 952 1,904 0 44 52,799 2,323,1711978 2 100 1,943 3,886 2 0       2 80,458 160,9161979 15 71 27,285 409,280 100 6 29 26,172 157,030 38 21 19,490 409,2801980 1 25 1,723 1,723 1 3 75 43,457 130,372 99 4 33,024 132,0951981 23 92 22,565 518,987 99 2 8 2,735 5,470 1 25 20,978 524,4571982 5 100 9,007 45,036 40 0 5 22,457 112,2831983 7 70 7,364 51,551 100 3 30 22,416 67,247 130 10 5,155 51,5511984 25 83 4,073 101,823 94 5 17 1,407 7,034 6 30 3,629 108,8571985 23 68 14,242 327,570 99 11 32 445 4,896 1 34 9,778 332,4661986 48 91 8,725 418,784 92 5 9 7,421 37,105 8 53 8,602 455,8891987 19 90 5,571 105,846 69 2 10 23,745 47,491 31 21 7,302 153,3371988 59 91 34,878 2,057,818 99 6 9 2,660 15,959 1 65 31,904 2,073,7771989 6 46 6,866 41,198 76 7 54 1,847 12,930 24 13 4,164 54,1271990 150 95 19,488 2,923,251 94 8 5 22,828 182,625 6 158 19,657 3,105,8761991 106 91 15,214 1,612,696 97 11 9 4,412 48,530 3 117 14,199 1,661,2261992 20 67 4,864 97,278 73 10 33 3,636 36,364 27 30 4,455 133,6431993 90 98 7,996 719,613 100 2 2 497 993 0 92 7,833 720,6061994 70 91 3,735 261,447 98 7 9 789 5,525 2 77 3,467 266,9721995 19 76 1,886 35,825 89 6 24 744 4,464 11 25 1,612 40,289

37

Appendix A (continued)

Lightning-caused fires Human-caused fires All firesAcres burned Acres burned Acres burned

Year No.% all fires

Avg. per fire

Total per year

% all acres No.

% all

firesAvg.

per fireTotal per

year% all acres No.

Avg. per fire

Total per year

1996 49 75 8,580 420,444 69 16 25 11,760 188,159 31 65 9,363 608,6031997 89 94 20,612 1,834,429 99 6 6 2,837 17,020 1 95 19,489 1,851,4491998 12 80 10,009 120,107 99 3 20 326 978 1 15 8,072 121,0841999 66 85 14,684 969,173 98 12 15 2,061 24,735 2 78 12,742 993,9082000 35 90 21,033 736,158 98 4 10 3,680 14,719 2 39 19,253 750,8772001 4 22 2,347 9,389 4 14 78 14,977 209,675 96 18 12,170 219,0642002 69 83 23,053 1,590,631 79 14 17 30,929 433,005 21 83 24,381 2,023,6362003 30 73 18,413 552,381 96 11 27 2,214 24,353 4 41 14,067 576,7342004 129 92 51,081 6,589,435 99 11 8 7,075 77,823 1 140 47,623 6,667,2582005 166 94 28,621 4,751,094 100 10 6 1,037 10,373 0 176 27,054 4,761,4672006 23 72 5,488 126,231 47 9 28 15,811 142,299 53 32 8,392 268,5302007 101 92 5,812 586,991 88 9 8 8,981 80,826 12 110 6,071 667,8172008 43 83 2,202 94,683 98 9 17 176 1,584 2 52 1,851 96,2672009 87 85 33,442 2,909,485 98 15 15 4,113 61,702 2 102 29,129 2,971,1872010 149 78 6,615 985,644 76 41 22 7,629 312,776 24 190 6,834 1,298,4202011 68 93 3,998 271,891 90 5 7 5,810 29,048 10 73 4,122 300,9392012 49 89 5,117 250,735 86 6 11 7,003 42,021 14 55 5,323 292,7562013 115 93 9,996 1,149,493 88 9 7 18,007 162,067 12 124 10,577 1,311,5602014 14 50 615 8,605 3 14 50 20,002 280,024 97 28 10,308 288,6292015 302 90 16,947 5,118,049 99 32 10 902 28,872 1 334 15,410 5,146,9212016 130 87 3,765 489,394 98 20 13 465 9,302 2 150 3,325 498,697Total

1940-2016 2968 57,561,399 504 8,813,588 3472 66,320,073

38

Appendix B. Area burned and number of lightning fires within physiographic provinces of Alaska during four periods, 1940-2016.

1940-1968 1969-1984 1985-2000 2001-2016Physiographic province Acres Fires (ac) n Fires (ac) n Fires (ac) n Fires (ac) nArctic Coastal Plain 18,000,712 0 0 11,554 1 0 0 264,114 16Arctic Foothills 25,604,664 0 0 12,611 2 109,338 5 287,049 16Arctic Mountains 35,436,814 559,230 18 1,707,406 90 1,438,302 69 1,873,371 221Northern Plataeus 49,329,724 40,113,365 330 18,781,119 213 49,754,191 847 118,469,663 1176Western Alaska 114,024,905 73,604,599 620 67,373,253 690 45,943,958 1125 112,212,590 1983Seward Peninsula 12,351,323 2,515,616 8 3,398,902 43 548,834 17 185,031 30Bering Shelf 19,175,297 726,698 5 241,473 29 120,866 26 1,228,938 87Ahklum Mountains 7,207,397 0 0 0 0 22,230 6 20,882 4Alaska-Aleutian 24,326,237 46,540 7 145,456 7 387,257 35 1,892,542 77Coastal Trough 22,139,020 37,651 3 14,885 1 2,617 4 211,110 28Pacific Border Ranges 43,031,957 14,069 1 0 0 6,745 2 206,612 16

Totals 992   1076   2136   3654

39

Appendix C. Area burned and number of lightning fires within physiographic section of Alaska during four periods, 1940-2016.

1940-1968 1969-1984 1985-2000 2001-2016Physiographic province Acres Fires (ac) n Fires (ac) n Fires (ac) n Fires (ac) nArctic Coastal Plain 18,000,712 0 0 11,554 1 0 0 264,114 5Arctic Foothills 25,604,664 0 0 12,611 2 109,338 5 287,049 16DeLong Mountains 2,831,326 0 0 65,631 12 0 0 52,941 8Noatak Lowlands 2,494,893 0 0 531,377 41 584,357 14 415,318 89Baird Mountains 3,769,271 4,156 1 335,909 15 280,171 9 227,793 27Central and Eastern Brooks Range 23,753,201 37,150 7 807,676 23 165,247 27 315,255 59Ambler-Chandalar Ridge and Lowland 2,588,123 3,419,250 14 807,820 21 741,102 27 1,322,645 68Porcupine Plateau 12,150,157 12,697,137 58 1,321,289 45 13,355,794 163 20,378,926 219Ogilvie Mountains 1,538,248 447,984 21 295,127 16 1,617,472 69 6,803,105 121Tintina Valley 735,708 37,772 3 0 0 100,668 4 678,205 26Yukon-Tanana Upland 17,836,114 5,177,892 96 636,984 28 9,101,244 278 35,619,422 369Northway-Tanacross Lowland 1,980,801 49,967 7 96,691 3 403,185 19 1,488,541 34Yukon Flats 9,642,547 18,327,007 118 3,880,220 75 28,655,052 274 47,275,662 362Rampart Trough 396,352 948 1 0 0 2,376,179 29 2,674,246 30Kokrine-Hodzana Highlands 6,928,716 13,038,562 96 14,573,488 78 7,326,786 170 39,306,321 304Kanuti Flats 1,321,033 962,280 24 7,371,294 31 4,366,543 45 6,087,180 52Tozitna-Melozitna Lowland 673,649 16,192,171 36 17,507,062 60 2,525,860 53 14,437,389 88Indian River Upland 4,080,709 11,470,462 93 22,669,546 111 3,161,545 105 13,976,139 160Pah River 2,690,122 742,608 7 4,895,042 67 1,774,626 74 618,575 72Koyukuk Flats 4,680,524 12,626,027 91 14,673,247 91 2,573,618 69 12,454,652 150Kobuk-Selawik Lowland 6,038,625 966,228 21 3,166,383 70 2,255,675 37 883,177 65Selawik Hills 588,896 609,453 4 957,808 13 434 2 150 1Buckland River Lowland 962,080 0 0 672,712 15 8,516 2 186,205 12Nulato Hills 14,029,963 17,454,497 47 2,295,413 61 169,089 58 1,689,905 121Tanana-Kuskokwim Lowland 10,630,039 2,182,332 73 7,982,860 106 5,878,607 234 29,405,197 397Nowitna Lowland 2,401,327 1,258,280 36 34,778 12 2,456,995 63 10,123,431 145

40

Appendix C (continued)

1940-1968 1969-1984 1985-2000 2001-2016Physiographic province Acres Fires (ac) n Fires (ac) n Fires (ac) n Fires (ac) nKuskokwim Mountains 22,553,912 23,150,462 244 3,337,681 163 24,471,185 457 40,936,223 838

Innoko Lowlands 3,305,500 2,364,805 26 256,780 29 2,771,368 29 3,928,336 58Nushagak-Big River

Hills 9,654,481 249,111 14 45,714 10 423,675 40 2,369,031 72Holitna Lowland 1,654,566 572,362 8 5,522 2 1,057,429 5 408,105 27

Nushagak-Bristol Bay Lowlands 10,407,034 118,893 4 1,723 1 49,605 8 24,198 8

Seward Peninsula 12,351,323 2,515,616 8 3,927,066 49 947,999 25 294,510 36Yukon-Kuskokwim

Coastal Lowland 19,175,297 726,698 5 241,473 29 120,866 26 1,228,938 87Ahklun Mountains 7,207,397 0 0 0 0 22,230 6 20,882 4

Alaska Range (southern) 9,166,793 0 0 2,586 1 10,894 1 4,416 3

Alaska Range (central and eastern) 10,654,261 0 0 0 0 8,547 1 121,390 9

Northern Foothills, Alaska Range 2,524,382 1,239 1 46,179 3 102,053 17 677,560 59

Cook Inlet-Susitna Lowland 5,887,213 0 0 0 0 0 0 142,818 13

Broad Pass Depression 597,835 0 0 0 0 0 0 151 1Gulkana Upland 1,658,825 4,800 1 0 0 0 0 1,546 7

Copper River Lowland 4,078,029 202,216 3 14,885 1 2,617 4 147,063 12Wrangell Mts 3,461,397 0 0 14,885 1 0 0 1,260 1

Kenai-Chugach Mountains 16,373,099 14,069 1 0 0 6,745 2 262,550 20

Totals 1169   1286   2451   4255

41

Appendix D. Size and identification number of fire weather zones in Alaska.

Zone Zone ID AcresWestern Kenai Peninsula 121 2,921,690Western Prince William Sound 125 4,982,272Copper River Basin 141 20,701,590Susitna Valley 145 11,451,616Middle Kuskokwim Valley 153 11,031,598Kuskokwim Delta 155 13,078,923Greater Bristol Bay 162 23,864,139Western Alaska Range 163 8,986,170Central Beaufort Sea Coast 203 2,813,697Northeastern Brooks Range 206 17,886,973Chukchi Sea Coast 207 2,606,049Lower Kobuk and Noatak Valleys 208 7,740,565Baldwin Peninsula and Selawik Valley 209 1,771,811Northern and Interior Seward Peninsula 210 11,013,125Southern Seward Peninsula Coast 211 801,581Eastern Norton Sound and Nulato Hills 212 6,129,555St Lawrence Island and Bering Strait Coast 213 2,482,977Yukon Delta 214 7,034,300Lower Yukon Valley 215 11,551,525Lower Koyukuk and Middle Yukon Valleys 216 18,208,744Upper Kobuk and Noatak Valleys 217 12,038,672Southeastern Brooks Range 218 17,720,965Upper Koyukuk Valley 219 9,070,148Yukon Flats and Surrounding Uplands 220 20,045,303Central Interior 221 11,320,383Middle Tanana Valley 222 3,112,708Deltana and Tanana Flats 223 2,559,178Upper Tanana Valley and the Fortymile Country 224 15,190,182Denali 225 4,398,584Eastern Alaska Range 226 6,670,095Upper Kuskokwim Valley 227 7,367,388

42

Appendix E. Area burned and number of lightning fires within fire weather zones of Alaska during four periods, 1940-2016.

1940-1968 1969-1984 1985-2000 2001-2016Fire weather zone Fires (ac) n Fires (ac) n Fires (ac) n Fires (ac) nBaldwin Peninsula and Selawik Valley 67,545 1 161,751 13 3,533 1 105 3

Central Beaufort Sea Coast 0 0 0 0 0 0 2,386 2

Central Interior 725,254 39 851,273 28 1,240,727 131 3,973,202 337Chukchi Sea Coast 11,711 2 3,951 4Copper River Basin 37,651 3 14,885 1 8,285 4 91,427 24Deltana and Tanana Flats 18,387 3 9,897 3 75,194 16 337,644 35

Denali 6,557 2 11,819 2 42,885 28 162,500 61Eastern Alaska Range 17,731 4 35,627 2 42,045 8 61,715 10Eastern Norton Sound and Nulato Hills 138,894 9 190,494 20 15,498 24 112,530 24

Greater Bristol Bay 137,244 6 6,377 2 49,188 13 49,917 15Kuskokwim Delta 9,270 1 23,334 7 13,156 11 246,525 50Lower Kobuk and Noatak Valleys 15,875 2 228,674 32 129,998 15 139,473 60

Lower Koyukuk and Middle Yukon Valleys 2,421,785 77 1,431,037 59 1,500,797 157 3,016,056 302

Lower Yukon Valley 2,417,417 31 269,135 41 507,132 66 1,655,532 120Middle Kuskokwim Valley 369,271 22 148,181 14 1,156,263 68 898,140 118

Middle Tanana Valley 179,540 12 72,946 5 87,447 24 705,574 43Northeastern Brooks Range 0 0 0 0 0 0 263,016 6

Northern and Interior Seward Peninsula 589,271 4 1,259,039 55 180,805 20 191,934 40

Northwestern Brooks Range 0 0 12,611 2 101,498 3 26,614 8

43

Appendix E (continued)

1940-1968 1969-1984 1985-2000 2001-2016Fire weather zone Fires (ac) n Fires (ac) n Fires (ac) n Fires (ac) nSoutheastern Brooks Range 236,223 9 121,965 15 200,154 33 629,365 72

Southern Seward Peninsula Coast 0 0 0 0 0 0 178 1

St Lawrence Island and Bering Strait Coast 44,704 1 0 0 0 0 0 0

Susitna Valley 0 0 0 0 0 0 10,442 3Upper Kobuk and Noatak Valleys 115,729 9 699,224 60 328,394 47 260,446 133

Upper Koyukuk Valley 978,402 31 1,394,326 46 1,271,797 104 2,724,788 169Upper Kuskokwim Valley 160,964 12 488,984 18 852,596 74 1,080,184 136

Upper Tanana Valley and the Fortymile Country

628,477 34 187,606 10 822,837 129 3,345,469 176

Western Alaska Range 5,876 1 37,695 8 34,718 10 144,186 30Western Kenai Peninsula 0 0 0 0 0 0 53,157 10

Western Prince William Sound 0 0 0 0 43 1 0 0

Yukon Delta 6,086 2 27,638 9 13,130 10 115,120 21Yukon Flats and Surrounding Uplands 1,503,459 46 702,033 33 4,006,985 222 5,295,137 298

44