Nevada Greenhouse Gas Inventory and Reference Case Projections

FINAL Nevada GHG Inventory and Reference Case Projection
CCS, July 2007
gases were converted to their CO 2 equivalents and summed to estimate total emissions from
fires. The nitrous oxide estimate was made assuming that N 2 O was 1% of the emissions of NO x
from the WRAP study. The 1% estimate is a common rule of thumb for the N 2 O content of NO x
from combustion sources.
The results for 2002 are that fires contributed about 0.23 MMtCO 2 e of methane and nitrous oxide
from about 88,958 acres burned (82,163 acres by wildfires). About 94% of the CO 2 e was
contributed by CH 4 . For the purposes of comparison, another 2002 estimate was made using
emission factors from a 2001 global biomass burning study 106 and the total tons of biomass
burned from the 2002 WRAP fires emissions inventory. This estimate is nearly 0.27 MMtCO 2 e
showing good agreement with the estimate above; however, there were about equal contributions
from methane and nitrous oxide on a CO 2 e basis.
Note that the 2002 level of activity compares to almost 950,000 acres burned in Nevada in
1996. 107 Given the large swings in fire activity from year to year and the current lack of data for
multiple years, CCS did not include these estimates in with the annual forestry flux estimates
presented in the emissions summaries of this report. However, on the basis of total acres burned
in 1996 and 2002, it appears that fires contribute on the order of 0.2 – 2.0 MMtCO 2 e annually in
NV from methane and nitrous oxide emissions.
Key Uncertainties
It is important to note that there were methodological differences in the two FIA cycles that can
produce different estimates of forested area and carbon density. For example, in the Rocky
Mountain Region of the US, the FIA program modified the definition of forest cover for the
woodlands class of forestland. Earlier FIA cycles defined woodlands as having a tree cover of at
least 10%, while the newer sampling methods used a woodlands definition of tree cover of at
least 5% (leading to more area being defined as woodland). In woodland areas, the earlier FIA
surveys might not have inventoried trees of certain species or with certain tree form
characteristics (leading to differences in both carbon density and forested acreage). Also, surveys
since 1999 include all dead trees on the plots, but data prior to that are variable in terms of these
data. The modifications to FIA surveys are a result of an expanded focus in the FIA program,
which historically was only concerned with timber resources, while more recent surveys have
aimed at a more comprehensive gathering of forest biomass data.
The effect of these changes in survey methods has not been comprehensively estimated by the
USFS. In states like Nevada that are in the Rocky Mountain Region and have substantial areas of
woodlands, the change in definition could contribute significantly to the increases seen in
forested area, which would translate into increases in CO 2 pools and large net negative CO 2
fluxes. For these reasons, the USFS provided flux estimates separately for woodlands, so that the
relative influence of the woodlands class on total net CO 2 fluxes in NV could be discerned. As
shown in Table H2, the contribution from the woodland areas drives a significant fraction of the
flux estimate statewide (over 75%). Given the modifications to the FIA survey methods, the
forest flux estimates for Nevada (-7.7 MMtCO 2 ) may be viewed as high.
106 M. O. Andreae and P. Merlet, “Emission of trace gases and aerosols from biomass burning”, Global
Biogeochemical Cycles, Vol. 15, No. 4, pp. 955-966, December 2001.
107 1996 Fire Emission Inventory, Draft Final Report, prepared by Air Sciences, Inc. for the Western Regional Air
Partnership, December 2002.
Nevada Division of 71 Center for Climate Strategies
Environmental Protection
www.climatestrategies.us