3.2 Impact and Restoration Modelling
37
where:
• pexp: Probability that the exposure will occur
• plet: Probability of lethal effect at the given exposure
• N: VEC unit in the grid cell. Population fraction (for sea surface and water column)
km coastline (for shoreline types) or km
2 (for seafloor habitats).
• The calculation is carried out for each Sim (simulation), cell, comp (compartment)
and for each VEC.
For each compartment and resource, the impact Imp is calculated for each grid
cell in each simulation. For the month(s) that are covered by the oil spill simulation,
results are reported in the cells with exposure to the VEC that has abundance above
zero in the cell in the given month.
Although the impact calculations follow the same basic framework of Eq. 3.1,
the functions used for calculating the factors pexp and plet values are different in the
four compartments, reflecting that exposure routes and mechanisms of lethal action
are different in the four compartments as well as between different resources and/or
resource groups. Each compartment uses different relevant oil drift simulation input
parameters in the exposure calculations.
As stated in the basic principles in Chap. 1, ERA Acute provides the opportunity
to use different levels of detailing based on availability of resource data (see Figs. 3.2
and 3.3).
• Level A.1: If VEC data are omitted, ERA Acute assumes that sensitive resources
are present in all cells in the analysis area (N = 1, ref Eq. 3.1), thus impact is
dependent on exposure and lethality calculations for each cell.
• Level A.2: If the data sets are available in polygons with data on presence or no
presence of biological resource data (N = 1 or N = 0, ref Eq. 3.1). Compared to
A1, A2 will calculate impact only in cells where resources are present, eliminating
cells with no presence.
• Level A.3: Fraction of VEC population present in the cell, adding up to N = 1
(100%) over all cells for sea surface and water column, length of coastal VEC
type for shoreline or area of seafloor habitat. This level will provide an impact
assessment of the total fraction of the population lost or total shoreline or seafloor
impact. The data adaption (N-value) will directly affect the numerical value of
the result and comparisons between compartments must be used with caution.
3.2.2 Step B: Impact Duration Modelling
The duration of the impact is calculated in step B, where the following time factors
are defined:
• Impact time (t imp ), the time from the spill until full impact is seen (usually set to
1 year for a full annual cycle)
• Lag-time (t lag ), the time from full impact until recovery can start (where relevant)
37
where:
• pexp: Probability that the exposure will occur
• plet: Probability of lethal effect at the given exposure
• N: VEC unit in the grid cell. Population fraction (for sea surface and water column)
km coastline (for shoreline types) or km
2 (for seafloor habitats).
• The calculation is carried out for each Sim (simulation), cell, comp (compartment)
and for each VEC.
For each compartment and resource, the impact Imp is calculated for each grid
cell in each simulation. For the month(s) that are covered by the oil spill simulation,
results are reported in the cells with exposure to the VEC that has abundance above
zero in the cell in the given month.
Although the impact calculations follow the same basic framework of Eq. 3.1,
the functions used for calculating the factors pexp and plet values are different in the
four compartments, reflecting that exposure routes and mechanisms of lethal action
are different in the four compartments as well as between different resources and/or
resource groups. Each compartment uses different relevant oil drift simulation input
parameters in the exposure calculations.
As stated in the basic principles in Chap. 1, ERA Acute provides the opportunity
to use different levels of detailing based on availability of resource data (see Figs. 3.2
and 3.3).
• Level A.1: If VEC data are omitted, ERA Acute assumes that sensitive resources
are present in all cells in the analysis area (N = 1, ref Eq. 3.1), thus impact is
dependent on exposure and lethality calculations for each cell.
• Level A.2: If the data sets are available in polygons with data on presence or no
presence of biological resource data (N = 1 or N = 0, ref Eq. 3.1). Compared to
A1, A2 will calculate impact only in cells where resources are present, eliminating
cells with no presence.
• Level A.3: Fraction of VEC population present in the cell, adding up to N = 1
(100%) over all cells for sea surface and water column, length of coastal VEC
type for shoreline or area of seafloor habitat. This level will provide an impact
assessment of the total fraction of the population lost or total shoreline or seafloor
impact. The data adaption (N-value) will directly affect the numerical value of
the result and comparisons between compartments must be used with caution.
3.2.2 Step B: Impact Duration Modelling
The duration of the impact is calculated in step B, where the following time factors
are defined:
• Impact time (t imp ), the time from the spill until full impact is seen (usually set to
1 year for a full annual cycle)
• Lag-time (t lag ), the time from full impact until recovery can start (where relevant)