40 yrs of wildfire trends in the Western Great Plains

The Western Great Plains

Geography

The Western Great Plains Land Resource Region and EPA Level 3 Ecoregions, within the broader US Great Plains (inset).

Environment

Proportion of rangeland cover by US Census tract from Reeves USFS range extent raster product.

Mean annual rainfall by US Census tract from monthly historical data, 1980-2020, from the TerraClimate dataset.

Table continues below

Ecoregion	Proportion rangeland (%)
High Plains	68
Nebraska Sand Hills	92
Northwestern Plains	80
Southwestern Tablelands	90

Mean annual precipitation (mm)
392
538
410
356

Fire incidence

These data are compiled from incident reports from various federal, state, and local agencies. With over 60,000 records it is by far the most complete fire history dataset in the region.

• Advantages
  • Huge number of incidents from many agencies
  • Broadest spatial representation
• Disadvantages
  • Spatial information limited to point given in incident record and reported burned area
  • No fire perimeter polygon allowing for mapping fire on top of ownership, vegetation, etc

Broad patterns in frequency and burned area

Total number of incidents per US Census tract, 1992-2020.

Total area burned by US Census tract, 1992-2020.

Temporal trends

Trends over time

Fires by month.

Causes and ignition sources

Total number of fires, fires per unit area of the total ecoregion, and total reported area burned for the four EPA L3 ecoregions of the Western Great Plains, 1992-2020. (continued below)

Ecoregion	Number of fires	Incidents per area
Northwestern Plains	34,069	0.13
Nebraska Sand Hills	1,423	0.03
High Plains	18,807	0.21
Southwestern Tablelands	6,276	0.1

Total burned area (ha)
2,104,345
251,136
342,945
394,098

Fire sizes

The vast majority of incidents in the database each burned a small area. In the NW Plains, only 5% of fires exceeded 65 ha. In the High Plains, only 5% of fires exceeded 12 ha.

Quantiles of burned areas for the four EPA L3 ecoregions of the Western Great Plains, 1992-2020.

Ecoregion	25%	50%	95%
Northwestern Plains	0.0405	0.2025	64.92
Nebraska Sand Hills	0.405	1.215	324
High Plains	0.0405	0.0405	12.15
Southwestern Tablelands	0.0405	0.0405	162

Burn area perimeters

These data are limited to incidents recorded as polygon GIS data of final fire perimeters available from BLM, USFS, MTBS, and NIFC.

• Advantages
  • Longer time series (1980-2021)
  • Actual fire perimeters allow quantification of burned area by ownership
• Disadvantages
  • Clearly many fewer incidents than the above dataset
  • Likely a spatial bias towards areas with lots of BLM & USFS resources

Trends across jurisdictions and agencies

Total area included in fire perimeters in four EPA L3 ecoregions of the Western Great Plains across land either designated as under tribal or federal or state agency management by the Bureau of Land Management’s Surface Management Agency shapefile, or land unassigned to an agency by the BLM, which includes, but is not necessarily limited to, privately-owned land.

Sum of area in wildfire perimeters by surface management authority in the Western Great Plains Land Resource Region, 1980-2020. Italic percentages below bars indicate the proportion of the total area of the region owned by each entity. BLM = Bureau of Land Management, Tribal = Native American reservations, BIA = Bureau of Indian Affairs, USFS = US Forest Service, FWS = Fish & Wildlife Service, NPS = National Park Service, DOD = Department of Defense.

Trends across public grazinglands

Proportion of federal grazing allotments in the Western Great Plains affected by a wildfire since 1980. Values are conservative as they are derived from the perimeter polygons dataset (2,665 wildfire events), and not the wildfire incident dataset (60,575 incidents).

Ecoregion	Agency	Grazing allotments affected by wildfire
High Plains	BLM	40 (16%)
High Plains	USFS	83 (24%)
Nebraska Sand Hills	BLM	1 (8%)
Nebraska Sand Hills	USFS	39 (80%)
Northwestern Plains	BLM	1032 (31%)
Northwestern Plains	USFS	365 (51%)
Southwestern Tablelands	BLM	8 (3%)
Southwestern Tablelands	USFS	23 (21%)

Number of grazing allotments affected each year by wildfire.

Top 5 largest fires for each ecoregion.

L3	year	name	ha
High Plains	2012	WELLNITZ	31273
High Plains	2012	WEST ASH	20863
High Plains	1989	FT.ROBINSON	18974
High Plains	2006	SIOUX COUNTY COMPLEX	13433
High Plains	2006	DAWES COUNTY COMPLEX	11300
Nebraska Sand Hills	2000	POWDER HORN	19671
Nebraska Sand Hills	1995	UNNAMED	11022
Nebraska Sand Hills	2012	REGION 24 COMPLEX	9278
Nebraska Sand Hills	2012	UNNAMED	7281
Nebraska Sand Hills	2012	TURNER TATANKA	6374
Northwestern Plains	2012	ASH CREEK	102553
Northwestern Plains	2017	BRIDGE COULEE	90072
Northwestern Plains	1984	HAWK CREEK	63850
Northwestern Plains	2003	MISSOURI BREAKS COMPLEX	55825
Northwestern Plains	2012	CHALKY	53694
Southwestern Tablelands	2008	BRIDGER	18863
Southwestern Tablelands	2018	MM 117	17331
Southwestern Tablelands	2011	BEAR SPRINGS CALLIE MARIE	14918
Southwestern Tablelands	2018	STATELINE	11547
Southwestern Tablelands	2006	CASA	11054

Jurisdictional variability

Examples of how internally variable jurisdictions are across wildfires on and off agency-owned and private land.

The 64,000-ha Hawk Creek Fire in eastern Montana was predominantly private, with BLM and state inholdings.

Among the largest fires in the ecoregion, the Ash Creek Fire spread across Tribal land, 2 federal agencies, state, and private.

Appendix

These graphs relate to the polygon data only, not the much-larger incidence dataset.

Temporal trends

Trends over time

Fires by month.

Causes, frequencies, and distribution

Causes of fire events as documented in the three source datasets.

Count of causes by data source.

source	cause	count
BLM	Human	418
BLM	Natural	779
BLM	Unknown	67
MTBS	Prescribed Fire	35
MTBS	Unknown	35
MTBS	Wildfire	706
nifc	Prescribed Fire	2
nifc	Unknown	1579
USFS	Arson	2
USFS	Campfire	8
USFS	Debris burning	9
USFS	Equipment use	79
USFS	Lightning	446
USFS	Misc.	112
USFS	Railroad	20
USFS	Smoking	5
USFS	Unknown	69

Number of fires and total area included in mapped fire perimeters for the four EPA L3 ecoregions of the Western Great Plains, 1980-2020. The proportion of the total ecoregion area burned is determined conservatively from uniquely-affected area, having accounted for repeated fires. (continued below)

Ecoregion	Number of fires	Total burned area (ha)
Northwestern Plains	2,096	1,823,009
Nebraska Sand Hills	146	139,868
High Plains	181	285,600
Southwestern Tablelands	133	256,751

% of ecoregion area burned
6.2%
2.5%
2.9%
2.9%