Like other countries in Europe, the United Kingdom experienced a heat wave
in early August 2003. Temperature records were broken. On 10 August,
Brogdale in Kent registered the United Kingdom’s highest temperature
ever recorded, of 38.5°C (101.3°F). In the south east of England,
maximum temperatures exceeded 32°C (89.6°F) on three consecutive
days between 4 and 6 August and then on five consecutive days between
8 and 12 August. Average August daily maximum temperature in the south
of England is around 21.2°C (70.2°F).
The Office for National Statistics (ONS) and its predecessors
have produced weekly national mortality data since the 1850s.
The purpose of our weekly deaths system is to provide a quick
estimate of any increase in deaths related to events such as
an influenza outbreak, or period of exceptional weather.
This paper will examine the impact of the 2003 heat wave on mortality
in England and Wales by age group and region. Air pollution and
temperature data will also be presented. The impact on mortality
will be compared with the rapid estimates produced by the weekly
deaths reporting system, which produced the first estimates of
excess mortality in England and Wales in August 2003.
The specific heat wave episode in August was defined as starting when
maximum daily Central England Temperature (CET) first exceeded average
values (1971 to 2000) by 8°C and ending when temperatures returned
to average levels. Excess mortality by age group and region was calculated
for the 10 day heat wave period (4 to 13 August 2003). In addition, a
value for excess mortality over the whole of July and August was also
calculated; no further calculations were made for this time period.
The mortality data, based on date of death, were adjusted on
a regional basis for the small proportion of deaths still unregistered
at the time of the analysis (approximately 1%). Deaths were assigned
to Government Office Regions (GORs) of residence.
Excess mortality was calculated as observed deaths minus the
expected mortality (average of deaths in the same years 1998
to 2002). The number of observed deaths was treated as a Poisson
variable. The 95% confidence limits for this value were then
subtracted from expected mortality to give confidence limits
for excess mortality. These limits were then calculated as a
percentage of expected mortality to give percentage confidence
limits for excess mortality.
The Met Office (the government agency that supplies meteorological
data on the weather and climate) supplied temperatures for each
GOR during the episode. Within each GOR, the maximum and minimum
of the daily maxima were then identified. Daily values were generated
for a national 5 km grid by interpolation of data from approximately
560 stations. Daily data for the London Weather Centre weather
station, and Central England Temperature (CET) were downloaded
from the British Atmospheric Data Centre. CET is representative
of a roughly triangular area in central England enclosed by the
cities of Preston, London and Bristol.
Measurements of the ambient air concentrations of ground level
ozone (daily maximum of a running 8 hour mean) and PM10 (particulate
matter of diameter less than 10 µm) (24 hour mean) were
obtained from the UK National Air Quality Archive. Air pollution
data was collected to allow a description only of a potential
confounder of the association with temperature.
Excess pollutant exposure was calculated as the difference between the
daily regional concentrations averaged over the episode and the equivalent
values observed during same period in 2002, when mean concentrations
were considered to be typical mean values for August.
Our current rapid weekly response system takes deaths which
have been registered in England and Wales in the previous week
and uses this to make an estimate of what the final registered
numbers will be . Estimates of excess were made by comparing
the registered deaths for each heat wave week in 2003 with the
average number of deaths registered for the same week in the
previous five years.
Subsequent analysis based on the day when deaths occurred will
include deaths which were registered immediately as well as deaths
which were registered in the weeks or months following the death.
Results: England and Wales
In England and Wales, there were 2139 excess deaths (16% increase, CI:
14% to 18%) during the August heat wave. The Central England Temperature
(CET) peaked at 31.5°C (88.7°F) on 9 August [FIGURE 1]. This
coincided with the peaks in the concentrations of ozone and PM10 in
England. The peak in daily deaths in England and Wales occurred two days
later on 11 August. In England and Wales, mortality in people over the
age of 75 increased by 22% (CI: 20% to 25%), more than the increase seen
for other age groups: (11% (CI: 6% to 15%) for the 0-64 age group and
3% (CI: -1% to 6%) for the 65-74 age group).
Overall in July there were fewer deaths than expected (-1%),
despite a slight increase in temperatures and mortality during
mid-July (FIGURE 1). Overall in August there was an excess of
5%. The increase in mortality over the heat wave episode (4-13
August) was followed by a decrease in deaths (-4%) in the period
24 to 29 August 2003.
The impact was greatest in the southern half of England, particularly
in London, where deaths for all ages increased by 42% (CI: 36% to 48%)
All regions had an excess for people over the age of 75 years. However
the greatest excess in the over 75 age group was in the London region
with a 59% (CI: 51% to 67%) increase. London experienced night time
temperatures of 26-27°C (79 to 81°C) during the heat wave, and
a maximum of 37.9°C (100.2°F) was recorded in London on 10
August ([FIGURE 2].
Concentrations of ozone and PM10 peaked in London on 6 and
8 August respectively [FIGURE 3]. Excess concentrations of PM10 and
ozone were highest in London and South East regions respectively [TABLE
Results: Comparison with initial estimates from the
weekly deaths reporting system
Data presented above [FIGURE 1] of the number of deaths occurring each
day show that deaths started to increase on 4 August 2003. This was included
in the week of 2 to 8 August (registration week 32). An estimate was
made of deaths registered in this week on Thursday 14 August. Our estimation
method takes into account short delays in data being sent to ONS .
The first clear indication of the upturn in deaths registered
following the hot temperatures was given by ONS on 21 August,
when an estimate of 907 excess deaths was made for registration
week 33, 8 to 15 August 2003. This estimate was of a similar
order of magnitude to the final excess mortality for that week.
However, this method did not indicate well the mortality excess
in the week following the heat wave. The initial estimate of excess
mortality was -75, but the final excess was 309 deaths for that
week. The excess in registrations in this week are likely to
be deaths that occurred in the previous two weeks but that were
not registered until week 34.
Table 3 shows initial and final information on death registrations in
England and Wales for the period 2 to 22 August 2003. Registrations
for the weeks before and after this period were around average levels.
Final number of deaths registered in weeks 32 to 34 (2 to 22 August)
were a total of 1828 deaths above average (average of the same week
over the previous five years). This final estimate of death registrations
is much higher than the initial estimated excess over the same period
of 910 deaths.
Subsequent work was based on the days when deaths actually occurred.
As already described, there were 2139 excess deaths over the
episode of 4 to 13 August, when temperatures were at their highest.
As expected, this was more than the final excess of 1828 deaths
registered over the three weeks, as deaths registered much later
than week 34 are included in the number of deaths by date of
The heat wave had a major effect on mortality in England and Wales, but
not to the extent of that observed in France where hot temperatures were
maintained for much longer .
Excess mortality was much greater than that observed with previous
heat waves in the UK. In Greater London it was estimated that
the 2003 heat wave was associated with a 40% increase in mortality
(all ages) compared with an excess of 16% in 1995 and 15% in
1976 [3,4]. Excess mortality in England and Wales was 10% in
1976, compared with 16% in 2003. Temperatures during the 1976
event were of a comparable magnitude, but the increasing ageing
population in England and Wales  may have contributed to the
increased 2003 excess.
The 2003 heat wave in the United Kingdom occurred relatively
late in the summer. Deaths in July overall were slightly below
expected levels. Temperatures and mortality did increase in mid-July,
and mortality was above what would normally be expected for the
time of year. However, high temperatures were not sustained,
and did not reach the levels seen in August. There was a small
dip in mortality following the heat wave in August, indicating
possible displacement of a proportion of deaths by the heat wave.
High ozone concentrations are an important co-exposure during
heat waves in England. High ozone concentrations were reported
during the 1976 heat wave . Excess exposure to ozone and PM10 were
recorded for all regions in England, most notably in London and
the South East. Between 21% and 38% of the excess deaths (where
excess deaths were predictions based on previous time series
studies of air pollution and mortality) in the 2003 heat wave
were estimated to be attributable to ozone and PM10,
although that study assumed no interaction between high temperatures
and high pollutant exposures . This study has not attempted
to separate out the effects of pollutants and temperature.
Cities are usually more affected by increasing temperatures
than surrounding areas where building density is lower . The
nocturnal urban heat island in London is greatest in the summer
months, and has increased since the 1960s .
The elderly (over 75 years) are most vulnerable to heat related
mortality, as has been shown in other heat wave studies in the
UK  and in other countries . When older people live alone,
they may not receive the care they need during a heat wave (for
example, adequate hydration) and they are also unlikely to call
for medical attention, and therefore may die at home without
being admitted to hospital .
Smaller increases were seen in many regions in the 0-64 year
age group, which may reflect an increase in mortality in children
and infants who are also at risk from heat-related deaths ,
or an increase in mortality in sick adults (e.g., those with
chronic cardiorespiratory disease).
The 2003 data used for mortality is provisional. There is some
uncertainty about the number of deaths that have still not been
registered, but a reliable estimate of final values can be made.
The weekly deaths reporting system provided a useful indication
of the impact of the hot weather in England and Wales, although
initial figures were an underestimate. The peak in the number
of deaths occurring in England and Wales was on 11 August 2003;
the registration week which included this date showed a clear
excess (the system picked up the biggest impact week). Any heat
warning system would also need to make use of additional information
such as temperature data.
When deaths are registered the information is passed to ONS.
When a death is registered in a particular week it does not mean
that the death necessarily occurred in that week; some deaths
are registered in the weeks following the death. Data by date
of occurrences is not therefore available as rapidly as deaths
by date of registration. Estimates based on the numbers of deaths
registered for the week therefore provide a more timely indicator.
Initial figures by date of death were published in October 2003
As climate change continues, heat waves are very likely to increase
in frequency and intensity  and are likely to exacerbate
London’s urban heat island . The weekly deaths reporting
system can play a useful role as a quick i ndication of the impact
on mortality of an event such as a heat wave. The prevention
of deaths has been addressed in a heat wave plan that has recently
been published by the Department of Health .