Online Resource 9. Interactions of IGSM-CAM
Variability with MC1 Thresholds
Climatic Change Article: Quantifying and Monetizing Potential Climate Change
Policy Impacts on Terrestrial Ecosystem Carbon Storage and Wildfires in the
United States
Authors: David Mills, Russell Jones, Karen Carney, Alexis St. Juliana, Richard
Ready, Allison Crimmins, Jeremy Martinich, Kate Shouse, Benjamin DeAngelo, and
Erwan Monier
Corresponding author: David Mills, Stratus Consulting Inc.,
[email protected]
Fire within MC1 (a dynamic global vegetation model) occurs within a cell once
certain threshold conditions are satisfied. In order to provide greater insight into how
variability in meteorological data generated from the Integrated Global Systems
Model (IGSM) Community Atmospheric Model (CAM) is interacting with MC1 to
produce such large estimates of the area burned under different emission scenarios
and initializing conditions, we examine the projected value for the proportion of a cell
burned for the year 2100.
Figure 9.1 shows a map of the projected results for the proportion of the cell burned
produced by MC1 for the reference (REF) emission scenario in 2100 and identifies
the specific cell of interest that will be the subject for subsequent graphs of
information on transient meteorological values from IGSM-CAM. This cell was
selected because of the extremely high value for the proportion of the cell burned
projected by MC1 in 2100 in this scenario.
Fig. 9.1 Example of MC1 fire output for year 2100
Figure 9.2 shows 115 years of output values from MC1 for the proportion of a cell
burned for a single cell in north-central Nebraska (latitude 42.25 N, longitude
100.75 W, see Figure 9.1). This yearly graph indicates that the largest value for the
fraction of the cell burned, equivalent to the greatest area burned for the cell, occurs
in year 2100. Examining the climate inputs from IGSM-CAM for the REF emission
scenario in year 2100 (Figures 9.3 through 9.5), it appears that the threshold
conditions to initiate fire within MC1 were reached in the month of July and reflect
the combination of extremely high maximum and minimum temperatures (Figures 9.3
and 9.4, respectively) and very low precipitation in July and the preceding months
(Figures 9.5).
This multi-month combination of meteorological extremes in the summer of 2100 in
this cell appears to be unique across the evaluated time period of 2001–2115. For
example, as noted in Figures 9.3 (Tmax) and 9.4 (Tmin), July 2095 and 2100 in this cell
had almost identical average monthly temperatures; in both years Tmax values
exceeded 40°C (104°F) and 25°C (77°F) for Tmin. However, in 2100, July followed an
extremely hot June. Specifically, the Tmax value in this cell for June 2095 was just
over 30°C (86°F), while its counterpart in 2100 was ~ 37°C (~ 98°F) (see Figures 9.3
and 9.4).
Similarly, while monthly precipitation values for July 2095 and 2100 were both very
low (see Figure 9.5), with totals less than 50 mm (< 2 in), the 2100 season followed a
series of dry months (see Figure 9.5). Specifically, in May 2095, approximately
160 mm (6.3 in.) of precipitation was projected for this cell while projected values for
both May and June 2100 had less than 100 mm (3.9 in.) of precipitation. Therefore,
the prolonged period of dryness combined with very high temperatures in July 2100
was enough to pass the threshold needed to initiate a substantial fire compared to
other years.
Year 2100
Fraction of cell burned
Fig. 9.2 Output from MC1 showing proportion of cell burned by year
July 2100
July 2095
Fig. 9.3 Maximum average monthly temperature input to MC1 (Tmax)
July 2100
Fig. 9.4 Minimum average monthly temperature input to MC1 (Tmin)
May 2095
May and June 2100
July 2095
July 2100
Fig. 9.5 Average monthly precipitation input to MC1

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