6
1 Introduction to the Concepts and Use of ERA Acute
This will give a total population loss of seabirds/mammals or fish larvae loss for
each simulation. For the shoreline compartment, the impact is also summarized to a
total shoreline impact in kilometers, distributed on the various shoreline rankings of
Environmental Sensitivity Indexes (ESI) (NOAA 2002). Similarly, for the seafloor
compartment, the total impact is given in km
2 impacted for each benthic habitat or
community.
ERA Acute can use three levels of detail in the continuous-function impact calculations, depending on availability of data on VEC occurrence and distribution. Two
screening levels allow for ERA Acute risk assessment even if VEC data are limited
or even missing. Oil spill trajectory input data are needed at all levels, however, not
all analyses may require complex modelled input of both oil and VEC. Simplified oil
spill input data can be prepared manually for screening purposes or based on actual
knowledge from a spill.
Impact calculation level A.1 is used if there are no data on the presence of environmental resources available (no VEC data). It uses only the oil drift simulations to
determine exposure and potential mortality and assumes the most sensitive resource
is present in all cells as a conservative estimate of the potential risk area. This quantitative result is suitable for identifying areas at risk in a screening or early phase
project decision, or for identifying which area to focus on filling data gaps. It is
particularly useful in areas where no knowledge exists on the presence of VECs,
allowing ERA Acute to be used for screening purposes (see Sect. 2.3) or decision
support where a specific detail on particular species is not needed (see Sect. 3.2.1).
Parameters that relate to the sensitivity of the species are provided as default values
based on globally applicable data, e g. global VEC wildlife groups.
Impact calculation levels A.2 and A.3 use resource data to identify specifically
where impacts and risks to resources are highest. Level A.2, the second screening
level, includes knowledge and data of whether the most sensitive VEC is present or
not in the cell, thereby excluding cells with known non-presence of sensitive VEC
(see Sect. 1.4.2.2). At the most detailed level (A.3), the full-resolution data on VEC
abundance distributions are used (i.e. population fraction in each grid cell), providing
a more accurate measure of potentially impacted fractions of the VEC (population
loss, impacted coastline length or seafloor area). This is suitable for more detailed
studies, e.g. analyses in sensitive areas, detailed decision making etc. and are used
for further calculations in the next step, recovery time calculations (step B).
1.3.3.2 Recovery Estimation (Step B)
In the second main step (B), the duration of the impact (i.e. the total recovery time)
is calculated as three time-factors for each VEC; the impact time (t imp ) describes
the time until full impact is seen, lag time (t lag ) is the time before restoration can
commence (where relevant), and restoration time (t res ) is the time it takes for the
resource to recover from re-growth starts to pre-spill levels. For the four environmental compartments, different parameters and sub-models are used to calculate
restoration times. The restoration time for birds and marine mammals is calculated
1 Introduction to the Concepts and Use of ERA Acute
This will give a total population loss of seabirds/mammals or fish larvae loss for
each simulation. For the shoreline compartment, the impact is also summarized to a
total shoreline impact in kilometers, distributed on the various shoreline rankings of
Environmental Sensitivity Indexes (ESI) (NOAA 2002). Similarly, for the seafloor
compartment, the total impact is given in km
2 impacted for each benthic habitat or
community.
ERA Acute can use three levels of detail in the continuous-function impact calculations, depending on availability of data on VEC occurrence and distribution. Two
screening levels allow for ERA Acute risk assessment even if VEC data are limited
or even missing. Oil spill trajectory input data are needed at all levels, however, not
all analyses may require complex modelled input of both oil and VEC. Simplified oil
spill input data can be prepared manually for screening purposes or based on actual
knowledge from a spill.
Impact calculation level A.1 is used if there are no data on the presence of environmental resources available (no VEC data). It uses only the oil drift simulations to
determine exposure and potential mortality and assumes the most sensitive resource
is present in all cells as a conservative estimate of the potential risk area. This quantitative result is suitable for identifying areas at risk in a screening or early phase
project decision, or for identifying which area to focus on filling data gaps. It is
particularly useful in areas where no knowledge exists on the presence of VECs,
allowing ERA Acute to be used for screening purposes (see Sect. 2.3) or decision
support where a specific detail on particular species is not needed (see Sect. 3.2.1).
Parameters that relate to the sensitivity of the species are provided as default values
based on globally applicable data, e g. global VEC wildlife groups.
Impact calculation levels A.2 and A.3 use resource data to identify specifically
where impacts and risks to resources are highest. Level A.2, the second screening
level, includes knowledge and data of whether the most sensitive VEC is present or
not in the cell, thereby excluding cells with known non-presence of sensitive VEC
(see Sect. 1.4.2.2). At the most detailed level (A.3), the full-resolution data on VEC
abundance distributions are used (i.e. population fraction in each grid cell), providing
a more accurate measure of potentially impacted fractions of the VEC (population
loss, impacted coastline length or seafloor area). This is suitable for more detailed
studies, e.g. analyses in sensitive areas, detailed decision making etc. and are used
for further calculations in the next step, recovery time calculations (step B).
1.3.3.2 Recovery Estimation (Step B)
In the second main step (B), the duration of the impact (i.e. the total recovery time)
is calculated as three time-factors for each VEC; the impact time (t imp ) describes
the time until full impact is seen, lag time (t lag ) is the time before restoration can
commence (where relevant), and restoration time (t res ) is the time it takes for the
resource to recover from re-growth starts to pre-spill levels. For the four environmental compartments, different parameters and sub-models are used to calculate
restoration times. The restoration time for birds and marine mammals is calculated