heatwave events into the future, as characterized
by the indices.
Accounting for external drivers allows for the
exploration of a dynamic system which evolves
over time, subject to drivers such as climate
change, population changes, and land use management. The incorporation of GIS tools allows
for spatial variation in the measurement of risk,
where vulnerability, hazard, and exposure factors
may vary with location.
Through the creation of a framework which
can determine a level of heatwave risk, it is stipulated that an increased ability to understand and
implement risk mitigation strategies will be
yielded.
Given this definition of risk, the following
literature review seeks to cover the breadth of
indices used to define heatwave events and the
observed impact of the extreme temperature
events and, where attempts have been made, summarize progress in determining the relationship
between the events (indices) and their impacts.
Understanding current knowledge of impacts
and indices will aid in developing a framework
for assessing the risk to various stakeholders associated with heatwave events and how this risk may
change with different future scenarios.
Heatwave Indices
Efforts have been made to define and measure
heatwaves using a range of indices, with no consistent definition being used to evaluate these
events [15]. These indices were often created
such that the output of the index corresponds to
the damage the heatwave would cause on a specific sector [16]. There is no standardized index
for the assessment of heatwave impacts on health
[17] or indeed for any sector. The complexity of
industry-specific indices results in the loss of generality of such indices [16]. As the impact on
different sectors drives which atmospheric parameters of heatwaves are most relevant, it is necessary to use heatwave indices that best align with
the sector being considered. The choice of definition, and by extension index, is not trivial, with
the method of definition able to fundamentally
change the association of impacts to events
[4]. Tong et al. [18] show that for only a small
change in definition was able to have appreciable
impacts on the change in predicted health
outcomes.
Two common approaches to defining
heatwaves are established by Lee [4]:
1. Determine an absolute temperature which must
be exceeded over a set number of days.
2. Determine a relative temperature which must
be exceeded over a set number of days.
In defining the relative temperature, two
approaches are commonly used, either setting
the limit as a percentile of historical temperatures
(i.e., 90th percentile) or as a threshold above a
qualitative definition of “normal” temperatures.
Extensions to the above approaches may
include incorporating (i) a shorter period of higher
temperatures which must occur within the longer
period, in some cases referred to as a multiple
threshold index [16], (ii) overnight temperatures,
and/or (iii) shade temperatures.
Considerable work has been undertaken to create an index which best captures heatwave
impacts. Table 1 provides a summary of current
heatwave indices, the considerations made in the
calculation of each index, and whether the index
aims to capture a measure of the intensity of the
event. There are many indices and area-specific
thresholds adopted by different government bodies; however, Table 1 looks to capture the breadth
of unique measures, with preference to those captured in literature. For the purposes of evaluating
intensity, temperature-adjusted or average temperature measures are not considered as measuring
intensity.
Another distinction between indices is the output of the index. Indices are seen to provide a
binary yes/no classification of whether a heatwave
has occurred; some indices (the EHF, EEHD, and
EEHN) go further and provide a measure of the
intensity of the heatwave (typically by measuring
the level of the index above the defined threshold).
Many of the indices in Table 1 were created
with the intended application in health sectors;
Robinson [19] goes as far as to state that
Measuring Heatwaves and Their Impacts
457
by the indices.
Accounting for external drivers allows for the
exploration of a dynamic system which evolves
over time, subject to drivers such as climate
change, population changes, and land use management. The incorporation of GIS tools allows
for spatial variation in the measurement of risk,
where vulnerability, hazard, and exposure factors
may vary with location.
Through the creation of a framework which
can determine a level of heatwave risk, it is stipulated that an increased ability to understand and
implement risk mitigation strategies will be
yielded.
Given this definition of risk, the following
literature review seeks to cover the breadth of
indices used to define heatwave events and the
observed impact of the extreme temperature
events and, where attempts have been made, summarize progress in determining the relationship
between the events (indices) and their impacts.
Understanding current knowledge of impacts
and indices will aid in developing a framework
for assessing the risk to various stakeholders associated with heatwave events and how this risk may
change with different future scenarios.
Heatwave Indices
Efforts have been made to define and measure
heatwaves using a range of indices, with no consistent definition being used to evaluate these
events [15]. These indices were often created
such that the output of the index corresponds to
the damage the heatwave would cause on a specific sector [16]. There is no standardized index
for the assessment of heatwave impacts on health
[17] or indeed for any sector. The complexity of
industry-specific indices results in the loss of generality of such indices [16]. As the impact on
different sectors drives which atmospheric parameters of heatwaves are most relevant, it is necessary to use heatwave indices that best align with
the sector being considered. The choice of definition, and by extension index, is not trivial, with
the method of definition able to fundamentally
change the association of impacts to events
[4]. Tong et al. [18] show that for only a small
change in definition was able to have appreciable
impacts on the change in predicted health
outcomes.
Two common approaches to defining
heatwaves are established by Lee [4]:
1. Determine an absolute temperature which must
be exceeded over a set number of days.
2. Determine a relative temperature which must
be exceeded over a set number of days.
In defining the relative temperature, two
approaches are commonly used, either setting
the limit as a percentile of historical temperatures
(i.e., 90th percentile) or as a threshold above a
qualitative definition of “normal” temperatures.
Extensions to the above approaches may
include incorporating (i) a shorter period of higher
temperatures which must occur within the longer
period, in some cases referred to as a multiple
threshold index [16], (ii) overnight temperatures,
and/or (iii) shade temperatures.
Considerable work has been undertaken to create an index which best captures heatwave
impacts. Table 1 provides a summary of current
heatwave indices, the considerations made in the
calculation of each index, and whether the index
aims to capture a measure of the intensity of the
event. There are many indices and area-specific
thresholds adopted by different government bodies; however, Table 1 looks to capture the breadth
of unique measures, with preference to those captured in literature. For the purposes of evaluating
intensity, temperature-adjusted or average temperature measures are not considered as measuring
intensity.
Another distinction between indices is the output of the index. Indices are seen to provide a
binary yes/no classification of whether a heatwave
has occurred; some indices (the EHF, EEHD, and
EEHN) go further and provide a measure of the
intensity of the heatwave (typically by measuring
the level of the index above the defined threshold).
Many of the indices in Table 1 were created
with the intended application in health sectors;
Robinson [19] goes as far as to state that
Measuring Heatwaves and Their Impacts
457