671 lines
36 KiB
ReStructuredText
671 lines
36 KiB
ReStructuredText
.. _rst_Fire:
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Fire
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========
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The fire parameterization in CLM contains four components: non-peat
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fires outside cropland and tropical closed forests, agricultural fires
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in cropland, deforestation fires in the tropical closed forests, and
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peat fires (see :ref:`Li et al. 2012a <Lietal2012a>`,
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:ref:`Li et al. 2012b <Lietal2012b>`, :ref:`Li et al. 2013 <Lietal2013a>`,
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:ref:`Li and Lawrence 2017 <LiLawrence2017>` for details).
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In this fire parameterization, burned area is affected by climate and
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weather conditions, vegetation composition and structure, and human
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activities. After burned area is calculated, we estimate the fire impact,
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including biomass and peat burning, fire-induced vegetation mortality,
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adjustment of the carbon and nitrogen (C/N) pools, and fire emissions.
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.. _Non-peat fires outside cropland and tropical closed forest:
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Non-peat fires outside cropland and tropical closed forest
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---------------------------------------------------------------
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Burned area in a grid cell, \ :math:`A_{b}` (km\ :sup:`2` s :sup:`-1`),
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is determined by
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.. math::
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:label: 23.1
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A_{b} =N_{f} a
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where :math:`N_{f}` (count s\ :sup:`-1`) is fire
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counts in the grid cell; :math:`a` (km\ :sup:`2`) is average fire
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spread area of a fire.
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.. _Fire counts:
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Fire counts
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^^^^^^^^^^^^^^^^^^
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Fire counts :math:`N_{f}` is taken as
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.. math::
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:label: 23.2
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N_{f} = N_{i} f_{b} f_{m} f_{se,o}
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where :math:`N_{i}` ( count s\ :sup:`-1`) is the
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number of ignition sources due to natural causes and human activities;
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:math:`f_{b}` and :math:`f_{m}` (fractions) represent the availability
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and combustibility of fuel, respectively; :math:`f_{se,o}` is the
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fraction of anthropogenic and natural fires unsuppressed by humans and
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related to the socioeconomic conditions.
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:math:`N_{i}` (count s\ :sup:`-1`) is given as
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.. math::
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:label: 23.3
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N_{i} = \left(I_{n} +I_{a} \right) A_{g}
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where :math:`I_{n}` (count km\ :sup:`-2` s\ :sup:`-1`) and :math:`I_{a}`
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(count km\ :sup:`-2` s\ :sup:`-1`) are the number of natural and anthropogenic
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ignitions per km\ :sup:`2`, respectively; :math:`A_{g}` is the area of the
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grid cell (km\ :sup:`2`). :math:`I_{n}` is estimated by
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.. math::
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:label: 23.4
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I_{n} = \gamma \psi I_{l}
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where :math:`\gamma` \ =0.22 is ignition efficiency of cloud-to-ground
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lightning; :math:`\psi =\frac{1}{5.16+2.16\cos [3min(60,\lambda )]}` is the
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cloud-to-ground lightning fraction and depends on the latitude
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:math:`\lambda` (degrees) ; :math:`I_{l}` (flash km\ :sup:`-2` s\ :sup:`-1`) is
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the total lightning flashes. :math:`I_{a}` is modeled as a monotonic
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increasing function of population density:
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.. math::
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:label: 23.5
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I_{a} =\frac{\alpha D_{P} k(D_{P} )}{n}
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where :math:`\alpha =0.01` (count person\ :sup:`-1` mon\ :sup:`-1`) is the number of potential ignition sources by a
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person per month; :math:`D_{P}` (person km\ :sup:`-2`) is the population density; :math:`k(D_{P} )=6.8D_{P} ^{-0.6}` represents anthropogenic ignition
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potential as a function of human population density :math:`D_{P}` ; *n*
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is the seconds in a month.
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Fuel availability :math:`f_{b}` is given as
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.. math::
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:label: 23.6
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f_{b} =\left\{\begin{array}{c}
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{0} \\ {\frac{B_{ag} -B_{low} }{B_{up} -B_{low} } } \\ {1} \end{array}
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\begin{array}{cc} {} & {} \end{array}\begin{array}{c} {B_{ag} <B_{low} } \\ {\begin{array}{cc} {} & {} \end{array}B_{low} \le B_{ag} \le B_{up} } \\ {B_{ag} >B_{up} }
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\end{array}\right\} \ ,
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where :math:`B_{ag}` (g C m\ :sup:`-2`) is the biomass of combined leaf,
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stem, litter, and woody debris pools; :math:`B_{low}` = 105 g C m :sup:`-2`
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is the lower fuel threshold below which fire does not occur; :math:`B_{up}`
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= 1050 g C m\ :sup:`-2` is the upper fuel threshold above which fire
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occurrence is not limited by fuel availability.
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Fuel combustibility :math:`f_{m}` is estimated by
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.. math::
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:label: 23.7
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f_{m} = {f_{RH} f_{\beta}}, &\qquad T_{17cm} > T_{f}
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where :math:`f_{RH}` and :math:`f_{\beta }` represent the dependence of
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fuel combustibility on relative humidity :math:`RH` (%) and root-zone
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soil moisture limitation :math:`\beta` (fraction); :math:`T_{17cm}` is
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the temperature of the top 17 cm of soil (K) and :math:`T_{f}` is the
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freezing temperature. :math:`f_{RH}` is a weighted average of real time
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:math:`RH` (:math:`RH_{0}`) and 30-day running mean :math:`RH`
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(:math:`RH_{30d}`):
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.. math::
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:label: 23.8
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f_{RH} = (1-w) l_{RH_{0}} + wl_{RH_{30d}}
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where weight :math:`w=\max [0,\min (1,\frac{B_{ag}-2500}{2500})]`,
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:math:`l_{{RH}_{0}}=1-\max [0,\min (1,\frac{RH_{0}-30}{80-30})]`, and
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:math:`l_{{RH}_{30d}}=1-\max [0.75,\min (1,\frac{RH_{30d}}{90})]`.
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:math:`f_{\beta}` is given by
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.. math::
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:label: 23.9
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f_{\beta } =\left\{\begin{array}{cccc}
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{1} & {} & {} & {\beta\le \beta_{low} } \\ {\frac{\beta_{up} -\beta}{\beta_{up} -\beta_{low} } } & {} & {} & {\beta_{low} <\beta<\beta_{up} } \\
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{0} & {} & {} & {\beta\ge \beta_{up} }
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\end{array}\right\} \ ,
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where :math:`\beta _{low}` \ =0.85 and :math:`\beta _{up}` \ =0.98 are the
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lower and upper thresholds, respectively.
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For scarcely populated regions (:math:`D_{p} \le 0.1` person
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km :sup:`-2`), we assume that anthropogenic suppression on fire
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occurrence is negligible, i.e., :math:`f_{se,o} =1.0`. In regions of
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:math:`D_{p} >0.1` person km\ :sup:`-2`, we parameterize the
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fraction of anthropogenic and natural fires unsuppressed by human
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activities as
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.. math::
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:label: 23.10
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f_{se,o} =f_{d} f_{e}
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where :math:`{f}_{d}` and :math:`{f}_{e}` are the effects of the
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demographic and economic conditions on fire occurrence. The demographic
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influence on fire occurrence is
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.. math::
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:label: 23.11
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f_{d} =0.01 + 0.98 \exp (-0.025D_{P} ).
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For shrub and grass PFTs, the economic influence on fire occurrence is
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parameterized as a function of Gross Domestic Product GDP (k 1995US$
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capita\ :sup:`-1`):
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.. math::
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:label: 23.12
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f_{e} =0.1+0.9\times \exp [-\pi (\frac{GDP}{8} )^{0.5} ]
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which captures 73% of the observed MODIS fire counts with variable GDP
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in regions where shrub and grass PFTs are dominant (fractional coverage
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of shrub and grass PFTs :math:`>` 50%). In regions outside tropical
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closed forests and dominated by trees (fractional coverage of tree PFTs
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:math:`>` 50%), we use
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.. math::
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:label: 23.13
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f_{e} =\left\{\begin{array}{c}
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{0.39} \\ {0.79} \\ {1} \end{array}
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\begin{array}{cc} {} & {} \end{array}\begin{array}{c} {GDP > 20 } \\
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{ 8 < GDP \le 20 } \\ { GDP \le 8 }
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\end{array}\right\} \ ,
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to reproduce the relationship between MODIS fire counts and GDP.
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.. _Average spread area of a fire:
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Average spread area of a fire
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Fire fighting capacity depends on socioeconomic conditions and affects
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fire spread area. Due to a lack of observations, we consider the
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socioeconomic impact on the average burned area rather than separately
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on fire spread rate and fire duration:
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.. math::
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:label: 23.14
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a=a^{*} F_{se}
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where :math:`a^{*}` is the average burned area of a fire without
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anthropogenic suppression and :math:`F_{se}` is the socioeconomic
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effect on fire spread area.
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Average burned area of a fire without anthropogenic suppression is
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assumed elliptical in shape with the wind direction along the major axis
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and the point of ignition at one of the foci. According to the area
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formula for an ellipse, average burned area of a fire can be represented
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as:
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.. math::
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:label: 23.15
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a^{*} =\pi \frac{l}{2} \frac{w}{2} \times 10^{-6} =\frac{\pi u_{p}^{2} \tau ^{2} }{4L_{B} } (1+\frac{1}{H_{B} } )^{2} \times 10^{-6}
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where :math:`u_{p}` (m s\ :sup:`-1`) is the fire spread rate in the
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downwind direction; :math:`\tau` (s) is average fire duration; :math:`L_{B}`
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and :math:`H_{B}` are length-to-breadth ratio and head-to-back ratio of
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the ellipse; 10 :sup:`-6` converts m :sup:`2` to km :sup:`2`.
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According to :ref:`Arora and Boer (2005)<AroraBoer2005>`,
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.. math::
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:label: 23.16
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L_{B} =1.0+10.0[1-\exp (-0.06W)]
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where :math:`W`\ (m s\ :sup:`-1`) is the wind speed. According to
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the mathematical properties of the ellipse, the head-to-back ratio
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:math:`H_{B}` is
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.. math::
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:label: 23.17
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H_{B} =\frac{u_{p} }{u_{b} } =\frac{L_{B} +(L_{B} ^{2} -1)^{0.5} }{L_{B} -(L_{B} ^{2} -1)^{0.5} } .
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The fire spread rate in the downwind direction is represented as
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.. math::
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:label: 23.18
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u_{p} =u_{\max } C_{m} g(W)
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(:ref:`Arora and Boer, 2005<AroraBoer2005>`), where :math:`u_{\max }`
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(m s\ :sup:`-1`) is the PFT-dependent average maximum fire spread
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rate in natural vegetation regions; :math:`C_{m} =\sqrt{f_{m}}` and :math:`g(W)`
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represent the dependence of :math:`u_{p}` on fuel wetness and wind
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speed :math:`W`, respectively. :math:`u_{\max }` is set to 0.33
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m s :sup:`-1`\ for grass PFTs, 0.28 m s :sup:`-1` for shrub PFTs, 0.26
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m s\ :sup:`-1` for needleleaf tree PFTs, and 0.25 m s\ :sup:`-1` for
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other tree PFTs. :math:`g(W)` is derived from the mathematical properties
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of the ellipse and equation :eq:`23.16` and :eq:`23.17`.
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.. math::
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:label: 23.19
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g(W)=\frac{2L_{B} }{1+\frac{1}{H_{B} } } g(0).
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Since g(\ *W*)=1.0, and \ :math:`L_{B}` and :math:`H_{B}` are at their
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maxima \ :math:`L_{B} ^{\max } =11.0` and \ :math:`H_{B} ^{\max } =482.0`
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when :math:`W\to \infty` , g(0) can be derived as
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.. math::
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:label: 23.20
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g(0)=\frac{1+\frac{1}{H_{B} ^{\max } } }{2L_{B} ^{\max } } =0.05.
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In the absence of globally gridded data on barriers to fire (e.g.
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rivers, lakes, roads, firebreaks) and human fire-fighting efforts,
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average fire duration is simply assumed equal to 1 which is the observed
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2001–2004 mean persistence of most fires in the world
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(:ref:`Giglio et al. 2006 <Giglioetal2006>`).
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As with the socioeconomic influence on fire occurrence, we assume that
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the socioeconomic influence on fire spreading is negligible in regions
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of :math:`D_{p} \le 0.1` person km\ :sup:`-2`, i.e.,
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:math:`F_{se} = 1.0`. In regions of :math:`D_{p} >0.1` person
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km\ :sup:`-2`, we parameterize such socioeconomic influence as:
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.. math::
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:label: 23.21
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F_{se} =F_{d} F_{e}
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where :math:`{F}_{d}` and :math:`{F}_{e}` are
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effects of the demographic and economic conditions on the average spread
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area of a fire, and are identified by maximizing the explained
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variability of the GFED3 burned area fraction with both socioeconomic
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indices in grid cells with various dominant vegetation types. For shrub
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and grass PFTs, the demographic impact factor is
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.. math::
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:label: 23.22
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F_{d} =0.2+0.8\times \exp [-\pi (\frac{D_{p} }{450} )^{0.5} ]
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and the economic impact factor is
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.. math::
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:label: 23.23
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F_{e} =0.2+0.8\times \exp (-\pi \frac{GDP}{7} ).
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For tree PFTs outside tropical closed forests, the demographic and
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economic impact factors are given as
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.. math::
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:label: 23.24
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F_{d} =0.4+0.6\times \exp (-\pi \frac{D_{p} }{125} )
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and
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.. math::
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:label: 23.25
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F_{e} =\left\{\begin{array}{cc}
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{0.62,} & {GDP>20} \\ {0.83,} & {8<GDP\le 20} \\
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{1,} & {GDP\le 8}
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\end{array}\right. .
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Equations :eq:`23.22` - :eq:`23.25` reflect that more developed and more
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densely populated regions have a higher fire fighting capability.
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.. _Fire impact:
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Fire impact
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^^^^^^^^^^^^^^^^^^
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In post-fire regions, we calculate PFT-level fire carbon emissions from
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biomass burning of the :math:`j`\ th PFT, :math:`{\phi}_{j}` (g C s\ :sup:`-1`), as
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.. math::
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:label: 23.26
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\phi _{j} =A_{b,j} \mathbf{C}_{j} \bullet \mathbf{CC}_{j}
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where :math:`A_{b,j}` (km\ :sup:`2` \s\ :sup:`-1`) is burned area for
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the :math:`j`\ th PFT; **C**\ :sub:`j` =(:math:`C_{leaf}`, :math:`C_{stem}`,
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:math:`C_{root}`, :math:`C_{ts}`) is a vector with carbon density (g C km
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:sup:`-2`) for leaf, stem (live and dead stem), root (fine, live coarse
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and dead coarse root), and transfer and storage carbon pools as elements;
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:math:`\mathbf{CC}_{j}` = (:math:`\mathbf{CC}_{leaf}`,
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:math:`\mathbf{CC}_{stem}`, :math:`\mathbf{CC}_{root}`, :math:`\mathbf{CC}_{ts}`)
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is the corresponding combustion completeness factor vector
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(:numref:`Table PFT-specific combustion completeness and fire mortality factors`).
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Moreover, we assume that 50% and 28% of column-level litter and coarse woody
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debris are burned and the corresponding carbon is transferred to atmosphere.
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Tissue mortality due to fire leads to carbon transfers in two ways.
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First, carbon from uncombusted leaf, live stem, dead stem, root, and
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transfer and storage pools
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:math:`\mathbf{C^{'} _{j1}} ={(C_{{leaf}} (1-CC_{{leaf}} ) ,C_{{livestem}} (1-CC_{{stem}} ) ,C_{{deadstem}} (1-CC_{{stem}} ),C_{{root}} (1-CC_{{root}} ),C_{{ts}} (1-CC_{{ts}} ))}_{j}`
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(g C km\ :sup:`-2`) is transferred to litter as
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.. math::
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:label: 23.27
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\Psi _{j1} =\frac{A_{b,j} }{f_{j} A_{g} } \mathbf{C^{'} _{j1}} \bullet M_{j1}
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where
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:math:`M_{j1} =(M_{{leaf}} ,M_{{livestem,1}} ,M_{{deadstem}} ,M_{{root}} ,M_{{ts}} )_{j}`
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is the corresponding mortality factor vector (:numref:`Table PFT-specific combustion completeness and fire mortality factors`). Second,
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carbon from uncombusted live stems is transferred to dead stems as:
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.. math::
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:label: 23.28
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\Psi _{j2} =\frac{A_{b,j} }{f_{j} A_{g} } C_{livestem} (1-CC_{stem} )M_{livestem,2}
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where :math:`M_{livestem,2}` is the corresponding mortality factor
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(:numref:`Table PFT-specific combustion completeness and fire mortality factors`).
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Fire nitrogen emissions and nitrogen transfers due to fire-induced
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mortality are calculated the same way as for carbon, using the same
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values for combustion completeness and mortality factors. With CLM’s
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dynamic vegetation option enabled, the number of tree PFT individuals
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killed by fire per km\ :sup:`2` (individual km\ :sup:`-2`
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s\ :sup:`-1`) is given by
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.. math::
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:label: 23.29
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P_{disturb,j} =\frac{A_{b,j} }{f_{j} A_{g} } P_{j} \xi _{j}
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where :math:`P_{j}` (individual km\ :sup:`-2`) is the population
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density for the :math:`j` th tree PFT and :math:`\xi _{j}` is the
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whole-plant mortality factor
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(:numref:`Table PFT-specific combustion completeness and fire mortality factors`).
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.. _Agricultural fires:
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Agricultural fires
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-----------------------
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The burned area of cropland (km\ :sup:`2` s\ :sup:`-1`) is taken as :math:`{A}_{b}`:
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.. math::
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:label: 23.30
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A_{b} =a_{1} f_{se} f_{t} f_{crop} A_{g}
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where :math:`a_{1}` (s\ :sup:`-1`) is a constant; :math:`f_{se}` represents
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the socioeconomic effect on fires; :math:`f_{t}` determines the seasonality
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of agricultural fires; :math:`f_{crop}` is the fractional coverage of
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cropland. :math:`a_{1}` \ = 1.6x10\ :sup:`-4` \hr\ :sup:`-1`\ is estimated
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using an inverse method, by matching 1997-2004 simulations to the analysis
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of :ref:`van der Werf et al. (2010) <vanderWerfetal2010>` that shows the
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2001-2009 average contribution of cropland fires is 4.7% of the total
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global burned area.
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The socioeconomic factor :math:`f_{se}` is given as follows:
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.. math::
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:label: 23.31
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f_{se} =f_{d} f_{e} .
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Here
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.. math::
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:label: 23.32
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f_{d} =0.04+0.96\times \exp [-\pi (\frac{D_{p} }{350} )^{0.5} ]
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and
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.. math::
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:label: 23.33
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f_{e} =0.01+0.99\times \exp (-\pi \frac{GDP}{10} )
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are the effects of population density and GDP on burned area, derived
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in a similar way to equation :eq:`23.32` and :eq:`23.33`. :math:`f_{t}`
|
||
is set to 1 at the first time step during the climatological peak month
|
||
for agricultural fires (:ref:`van der Werf et al. 2010 <vanderWerfetal2010>`);
|
||
:math:`{f}_{t}` is set to 0 otherwise. Peak
|
||
month in this dataset correlates with the month after harvesting or the
|
||
month before planting. In CLM we use this dataset the same way whether
|
||
the CROP option is active or not, without regard to the CROP option’s
|
||
simulated planting and harvesting dates.
|
||
|
||
In the post-fire region, fire impact is parameterized similar to section
|
||
:numref:`Fire impact` but with combustion completeness factors and tissue
|
||
mortality factors for crop PFTs
|
||
(:numref:`Table PFT-specific combustion completeness and fire mortality factors`).
|
||
|
||
.. _Deforestation fires:
|
||
|
||
Deforestation fires
|
||
------------------------
|
||
|
||
CLM focuses on deforestation fires in tropical closed forests. Tropical
|
||
closed forests are defined as grid cells with tropical tree (BET and BDT tropical)
|
||
coverage :math:`>` 60% according to the FAO classification. Deforestation fires
|
||
are defined as fires caused by deforestation, including escaped
|
||
deforestation fires, termed degradation fires. Deforestation and
|
||
degradation fires are assumed to occur outside of cropland areas in
|
||
these grid cells. Burned area is controlled by the deforestation rate
|
||
and climate:
|
||
|
||
.. math::
|
||
:label: 23.34
|
||
|
||
A_{b} = b \ f_{lu} f_{cli,d} f_{b} A_{g}
|
||
|
||
where :math:`b` (s\ :sup:`-1`) is a global constant;
|
||
:math:`f_{lu}` (fraction) represents the effect of decreasing
|
||
fractional coverage of tree PFTs derived from land use data;
|
||
:math:`f_{cli,d}` (fraction) represents the effect of climate
|
||
conditions on the burned area.
|
||
|
||
Constants :math:`b` and :math:`{f}_{lu}` are calibrated
|
||
based on observations and reanalysis datasets in the Amazon rainforest
|
||
(tropical closed forests within 15.5 :sup:`o` S :math:`\text{-}` 10.5
|
||
:sup:`o` N, 30.5 :sup:`o` W :math:`\text{-}` 91 :sup:`o` W).
|
||
:math:`b` = 0.033 d\ :sup:`-1` and :math:`f_{lu}` is defined as
|
||
|
||
.. math::
|
||
:label: 23.35
|
||
|
||
f_{lu} = \max (0.0005,0.19D-0.001)
|
||
|
||
where :math:`D` (yr\ :sup:`-1`) is the annual loss of tree cover
|
||
based on CLM land use and land cover change data.
|
||
|
||
The effect of climate on deforestation fires is parameterized as:
|
||
|
||
.. math::
|
||
:label: 23.36
|
||
|
||
\begin{array}{ll}
|
||
f_{cli,d} \quad = & \quad \max \left[0,\min (1,\frac{b_{2} -P_{60d} }{b_{2} } )\right]^{0.5} \times \\
|
||
& \quad \max \left[0,\min (1,\frac{b_{3} -P_{10d} }{b_{3} } )\right]^{0.5} \times \\
|
||
& \quad \max \left[0,\min (1,\frac{0.25-P}{0.25} )\right]
|
||
\end{array}
|
||
|
||
where :math:`P` (mm d :sup:`-1`) is instantaneous precipitation, while
|
||
:math:`P_{60d}` (mm d\ :sup:`-1`) and :math:`P_{10d}` (mm d :sup:`-1`)
|
||
are 60-day and 10-day running means of precipitation, respectively;
|
||
:math:`b_{2}` (mm d :sup:`-1`) and :math:`b_{3}` (mm d :sup:`-1`) are
|
||
the grid-cell dependent thresholds of :math:`P_{60d}` and :math:`P_{10d}` ;
|
||
0.25 mm d :sup:`-1` is the maximum precipitation rate for drizzle.
|
||
:ref:`Le Page et al. (2010) <LePageetal2010>` analyzed the relationship
|
||
between large-scale deforestation fire counts and precipitation during 2003
|
||
:math:`\text{-}`\ 2006 in southern Amazonia where tropical evergreen trees
|
||
(BET Tropical) are dominant. Figure 2 in
|
||
:ref:`Le Page et al. (2010) <LePageetal2010>` showed that fires generally
|
||
occurred if both :math:`P_{60d}` and :math:`P_{10d}` were less than about
|
||
4.0 mm d :sup:`-1`, and fires occurred more frequently in a drier environment.
|
||
Based on the 30-yr (1985 to 2004) precipitation data in
|
||
:ref:`Qian et al. (2006) <Qianetal2006>`. The climatological precipitation
|
||
of dry months (P < 4.0 mm d :sup:`-1`) in a year over tropical deciduous
|
||
tree (BDT Tropical) dominated regions is 46% of that over BET Tropical
|
||
dominated regions, so we set the PFT-dependent thresholds of :math:`P_{60d}`
|
||
and :math:`P_{10d}` as 4.0 mm d :sup:`-1` for BET Tropical and 1.8 mm d
|
||
:sup:`-1` (= 4.0 mm d :sup:`-1` :math:`\times` 46%) for BDT Tropical, and
|
||
:math:`b`\ :sub:`2` and :math:`b`\ :sub:`3` are the average of thresholds
|
||
of BET Tropical and BDT Tropical weighted bytheir coverage.
|
||
|
||
The post-fire area due to deforestation is not limited to land-type
|
||
conversion regions. In the tree-reduced region, the maximum fire carbon
|
||
emissions are assumed to be 80% of the total conversion flux. According
|
||
to the fraction of conversion flux for tropical trees in the
|
||
tree-reduced region (60%) assigned by CLM4-CN, to reach the maximum fire
|
||
carbon emissions in a conversion region requires burning this region
|
||
about twice when we set PFT-dependent combustion completeness factors to
|
||
about 0.3 for stem [the mean of 0.2\ :math:`{-}`\ 0.4 used in
|
||
:ref:`van der Werf et al. (2010) <vanderWerfetal2010>`. Therefore, when
|
||
the burned area calculated from equation :eq:`23.36` is
|
||
no more than twice the tree-reduced area, we assume no escaped fires
|
||
outside the land-type conversion region, and the fire-related fraction
|
||
of the total conversion flux is estimated as
|
||
:math:`\frac{A_{b} /A_{g} }{2D}` . Otherwise, 80% of the total
|
||
conversion flux is assumed to be fire carbon emissions, and the biomass
|
||
combustion and vegetation mortality outside the tree-reduced regions
|
||
with an area fraction of :math:`\frac{A_{b} }{A_{g} } -2D` are set as in
|
||
section :numref:`Fire impact`.
|
||
|
||
.. _Peat fires:
|
||
|
||
Peat fires
|
||
---------------
|
||
|
||
The burned area due to peat fires is given as :math:`{A}_{b}`:
|
||
|
||
.. math::
|
||
:label: 23.37
|
||
|
||
A_{b} = c \ f_{cli,p} f_{peat} (1 - f_{sat} ) A_{g}
|
||
|
||
where :math:`c` (s\ :sup:`-1`) is a constant; :math:`f_{cli,p}` represents
|
||
the effect of climate on the burned area; :math:`f_{peat}` is the fractional
|
||
coverage of peatland in the grid cell; and :math:`f_{sat}` is the fraction
|
||
of the grid cell with a water table at the surface or higher. :math:`c` = 0.17
|
||
:math:`\times` 10 :sup:`-3` hr\ :sup:`-1` for tropical peat fires and
|
||
:math:`c` = 0.9 :math:`\times` 10 :sup:`-5` hr :sup:`-1` for boreal peat fires
|
||
are derived using an inverse method, by matching simulations to earlier
|
||
studies: about 2.4 Mha peatland was burned over Indonesia in 1997
|
||
(:ref:`Page et al. 2002 <Pageetal2002>`) and the average burned area of peat
|
||
fires in Western Canada was 0.2 Mha yr :sup:`-1` for 1980-1999
|
||
(:ref:`Turetsky et al. 2004 <Turetskyetal2004>`).
|
||
|
||
For tropical peat fires, :math:`f_{cli,p}` is set as a function of
|
||
long-term precipitation :math:`P_{60d}` :
|
||
|
||
.. math::
|
||
:label: 23.38
|
||
|
||
f_{cli,p} = \ max \left[0,\min \left(1,\frac{4-P_{60d} }{4} \right)\right]^{2} .
|
||
|
||
For boreal peat fires, :math:`f_{cli,p}` is set to
|
||
|
||
.. math::
|
||
:label: 23.39
|
||
|
||
f_{cli,p} = \exp (-\pi \frac{\theta _{17cm} }{0.3} )\cdot \max [0,\min (1,\frac{T_{17cm} -T_{f} }{10} )]
|
||
|
||
where :math:`\theta _{17cm}` is the wetness of the top 17 cm of soil.
|
||
|
||
Peat fires lead to peat burning and the combustion and mortality of
|
||
vegetation over peatlands. For tropical peat fires, based on
|
||
:ref:`Page et al. (2002) <Pageetal2002>`, about 6% of the peat carbon loss
|
||
from stored carbon is caused by 33.9% of the peatland burned. Carbon emissions
|
||
due to peat burning (g C m\ :sup:`-2` s\ :sup:`-1`) are therefore set as the
|
||
product of 6%/33.9%, burned area fraction of peat fire (s\ :sup:`-1`), and
|
||
soil organic carbon (g C m\ :sup:`-2`). For boreal peat fires, the carbon
|
||
emissions due to peat burning are set as 2.2 kg C m\ :sup:`-2` \ peat fire
|
||
area (:ref:`Turetsky et al. 2002 <Turetskyetal2002>`). Biomass combustion
|
||
and vegetation mortality in post-fire peatlands are set the same as section
|
||
:numref:`Fire impact` for non-crop PFTs and as section
|
||
:numref:`Agricultural fires` for crops PFTs.
|
||
|
||
.. _Fire trace gas and aerosol emissions:
|
||
|
||
Fire trace gas and aerosol emissions
|
||
-------------------------------------
|
||
CESM2 is the first Earth system model that can model the full coupling
|
||
among fire, fire emissions, land, and atmosphere. CLM5, as the land
|
||
component of CESM2, calculates the surface trace gas and aerosol emissions
|
||
due to fire and fire emission heights, as the inputs of atmospheric
|
||
chemistry model and aerosol model.
|
||
|
||
Emissions for trace gas and aerosol species x and the j-th PFT, :math:`E_{x,j}`
|
||
(g species s\ :sup:`-1`), are given by
|
||
|
||
.. math::
|
||
:label: 23.40
|
||
|
||
E_{x,j} = EF_{x,j}\frac{\phi _{j} }{[C]}.
|
||
|
||
Here, :math:`EF_{x,j}` (g species (g dm)\ :sup:`-1`) is PFT-dependent emission
|
||
factor scaled from biome-level values (Li et al., in prep, also used for FireMIP
|
||
fire emissions data) by Dr. Val Martin and Dr. Li. :math:`[C]` = 0.5
|
||
(g C (g dm)\ :sup:`-1`) is a conversion factor from dry matter to carbon.
|
||
|
||
Emission height is PFT-dependent: 4.3 km for needleleaf tree PFTs, 3 km for other
|
||
boreal and temperate tree PFTs, 2.5 km for tropical tree PFTs, 2 km for shrub
|
||
PFTs, and 1 km for grass and crop PFTs. These values are compiled from earlier
|
||
studies by Dr. Val Martin.
|
||
|
||
.. _Table PFT-specific combustion completeness and fire mortality factors:
|
||
|
||
.. table:: PFT-specific combustion completeness and fire mortality factors.
|
||
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| PFT | *CC*\ :sub:`leaf` | *CC*\ :sub:`stem` | *CC*\ :sub:`root` | *CC*\ :sub:`ts` | *M*\ :sub:`leaf` | *M*\ :sub:`livestem,1` | *M*\ :sub:`deadstem` | *M*\ :sub:`root` | *M*\ :sub:`ts` | *M*\ :sub:`livestem,2` | :math:`\xi`\ :sub:`j` |
|
||
+==================================+===========================+===========================+===========================+=========================+==========================+==============================+==============================+==========================+========================+==============================+=================================+
|
||
| NET Temperate | 0.80 | 0.30 | 0.00 | 0.50 | 0.80 | 0.15 | 0.15 | 0.15 | 0.50 | 0.35 | 0.15 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| NET Boreal | 0.80 | 0.30 | 0.00 | 0.50 | 0.80 | 0.15 | 0.15 | 0.15 | 0.50 | 0.35 | 0.15 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| NDT Boreal | 0.80 | 0.30 | 0.00 | 0.50 | 0.80 | 0.15 | 0.15 | 0.15 | 0.50 | 0.35 | 0.15 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BET Tropical | 0.80 | 0.27 | 0.00 | 0.45 | 0.80 | 0.13 | 0.13 | 0.13 | 0.45 | 0.32 | 0.13 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BET Temperate | 0.80 | 0.27 | 0.00 | 0.45 | 0.80 | 0.13 | 0.13 | 0.13 | 0.45 | 0.32 | 0.13 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BDT Tropical | 0.80 | 0.27 | 0.00 | 0.45 | 0.80 | 0.10 | 0.10 | 0.10 | 0.35 | 0.25 | 0.10 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BDT Temperate | 0.80 | 0.27 | 0.00 | 0.45 | 0.80 | 0.10 | 0.10 | 0.10 | 0.35 | 0.25 | 0.10 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BDT Boreal | 0.80 | 0.27 | 0.00 | 0.45 | 0.80 | 0.13 | 0.13 | 0.13 | 0.45 | 0.32 | 0.13 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BES Temperate | 0.80 | 0.35 | 0.00 | 0.55 | 0.80 | 0.17 | 0.17 | 0.17 | 0.55 | 0.38 | 0.17 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BDS Temperate | 0.80 | 0.35 | 0.00 | 0.55 | 0.80 | 0.17 | 0.17 | 0.17 | 0.55 | 0.38 | 0.17 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| BDS Boreal | 0.80 | 0.35 | 0.00 | 0.55 | 0.80 | 0.17 | 0.17 | 0.17 | 0.55 | 0.38 | 0.17 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| C\ :sub:`3` Grass Arctic | 0.80 | 0.80 | 0.00 | 0.80 | 0.80 | 0.20 | 0.20 | 0.20 | 0.80 | 0.60 | 0.20 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| C\ :sub:`3` Grass | 0.80 | 0.80 | 0.00 | 0.80 | 0.80 | 0.20 | 0.20 | 0.20 | 0.80 | 0.60 | 0.20 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| C\ :sub:`4` Grass | 0.80 | 0.80 | 0.00 | 0.80 | 0.80 | 0.20 | 0.20 | 0.20 | 0.80 | 0.60 | 0.20 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
| Crop | 0.80 | 0.80 | 0.00 | 0.80 | 0.80 | 0.20 | 0.20 | 0.20 | 0.80 | 0.60 | 0.20 |
|
||
+----------------------------------+---------------------------+---------------------------+---------------------------+-------------------------+--------------------------+------------------------------+------------------------------+--------------------------+------------------------+------------------------------+---------------------------------+
|
||
|
||
Leaves (:math:`CC_{leaf}` ), stems (:math:`CC_{stem}` ),
|
||
roots (:math:`CC_{root}` ) , and transfer and storage carbon
|
||
(:math:`CC_{ts}` ); mortality factors for leaves
|
||
(:math:`M_{leaf}` ), live stems (:math:`M_{livestem,1}` ),
|
||
dead stems (:math:`M_{deadstem}` ), roots
|
||
(:math:`M_{root}` ), and transfer and storage carbon
|
||
(:math:`M_{ts}` ) related to the carbon transfers from these pools
|
||
to litter pool; mortality factors for live stems
|
||
(:math:`M_{livestem,2}` ) related to the carbon transfer from live
|
||
stems to dead stems; whole-plant mortality factor (:math:`\xi _{j}` ).
|