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R E S E A R C H A R T I C L E

An analysis of heat index over Naples (Southern Italy)

in the context of European heat wave of 2003

R. Di Cristo

A. Mazzarella

R. Viola

Received: 14 October 2004 / Accepted: 16 March 2006 /

Published online: 17 October 2006 Springer Science+Business Media B.V. 2006

Abstract Two strong heat waves in the summer of 2003 determined elevated heat dis-

comfort conditions all across the Western Europe. In this context, the analysis of hourly

Heat Index values in the city of Naples (Southern Italy) showed prolonged heat discomfort

conditions during the second half of June 2003 and from the second half of July 2003 up to

the first week of September 2003, resulting in highest mortality rate for persons 75 years or

more.

Keywords Apparent temperature Heat index Heat wave Urban heat island

Introduction

During 2003 summer, most of Europe was affected by an extreme heat wave that increased

dramatically not only the land temperature, but also the frequency and duration of hot and

dry days. These conditions were part of a prolonged warm and dry spell that began in May

owing to a presence of an upper-level ridge of high pressure centred over the continent.

The persistence of this ridge was partly related to a prolonged positive phase of the Eastern

Atlantic teleconnection pattern (Levison and Waple 2004).

Particularly, the 2003 summer was characterized by two significant heat waves: the first

in June and the second during the latter half of July and the first half of August. The

coincidence of the JulyAugust heat wave with the normal peak in summer temperature

made this one more serious and caused an almost complete absence of rainfall (Levison

and Waple 2004). It is worth noting that the risk for heat-related mortality, already a

considerable public health threat, increases dramatically for the persons living in urban

environments because affected from the so-called urban heat island, responsible for heatdiscomfort higher than in surrounding suburban or rural areas.

R. Di Cristo (&) A. Mazzarella R. Viola

Department of Geophysics and Volcanology, University of Naples Federico II,

Largo S. Marcellino 10, 80138 Naples, Italy

e-mail: rdicrist@unina.it

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Nat Hazards (2007) 40:373379

DOI 10.1007/s11069-006-0033-7

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The aim of this paper is to analyze the heat index over Naples (Southern Italy), in the

context of European heat wave of 2003.

Data collection and method of analysis

The city of Naples (Fig. 1) has a Mediterranean-type climate with a mean air temperature

of about 17C, a relative humidity equal to 60% and a mean precipitation equal to 900 mm,

concentrated in the period from October to April. The bay of Naples faces the Tyrrhenian

Sea and almost the 90% of the precipitation systems move directly from the sea within a

sector from southeast to northwest (Palumbo and Mazzarella 1980). The summer climate

of Naples is influenced normally by the milder Azzorre anticyclone and, at times, by the

hotter African anticyclone, responsible for dangerous heat waves and medical emergency,

when the circulation becomes meridional.

The city of Naples has about 1,200,000 of inhabitants and its urban area is affected by apronounced heat island related to the dense building area distribution, the presence of

narrow streets, small parks and deep canyons and a particular architecture restricting the

free air circulation (Palumbo and Mazzarella 1981).

The first class Meteorological Observatory of University of Naples Federico II is

located in the centre of Naples (lat. 405048; long. 141531; altitude 50 m a.s.l.) and

continuously operating from 1872 until now. The availability of hourly meteorological data

has allowed a detailed description of the historical discomfort conditions that have affected

the city from 1872 up to 2004.

There are several variables involved in the assessment of the effects of heat on people(Burton 1944; Steadman 1979; Steadman 1984) that can be grouped in three main

typologies:

climatic variables (relative humidity, wind speed, insolation, air temperature, ground

temperature);

Fig. 1 Position of Naples in the Italian country

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physiological variables (human body temperature and mass, metabolic rate, transpi-

ration);

behaviour variables (clothing cover, clothing type, physical activity).

The Heat Index (Steadman1979) is usually simplified as a relationship between ambient

temperature and relative humidity versus skin (or apparent) temperature. As a result of this

procedure, there is a base relative humidity at which an apparent temperature feels like

the same air temperature, and increasing (or decreasing) humidity and temperature result in

increasing (or decreasing) apparent temperature. It is worth noting that the relative

humidity does not take into account the amount of water inside the air mass but only the

closeness to the saturation point and people do not feel the effective amount of vapour but

its closeness to the saturation point.

A multiple regression analysis was applied to Steadmans scheme to obtain the fol-

lowing simple formula that use the air temperature Tin F and the relative humidity R in

percentage, assuming a wind speed of 2.6 m/s (Rothfuzs 1990):

HI 42:379 2:04901523T 10:14333127R 0:22475541TR

6:83783 103T2 5:481717 102R2

1:22874 103T2R 8:5282 104TR2 1:99 106T2R2

Such a formula is applicable only when air temperature and humidity is higher than 26C

and 39%, respectively.

Results and discussion

Table1shows the values of apparent temperature computed by the heat index formula are

here used to estimate the discomfort conditions due to heat in Naples; Fig. 2shows the

mean monthly behaviour of mean and maximum apparent temperatures, measured from

June to September in the 18722004 intervals, while Fig. 3shows the mean annual ones.

A visual inspection of Figs. 2and3 shows that July is the month more affected by heat

waves and that the apparent temperatures of 2003 and 1950 are the highest and with a

comparable magnitude equal to about 29C. Both 2003 and 1950 summers were charac-

terised by meridional circulation with the dominant presence of the African anticycloneover the Mediterranean area in place of the milder Azzorre anticyclone (Guerrieri 1951;

Giuliacci 2003).

Table 1 Heat index ranges and related discomfort conditions

Heat index Colour in Figure 4 & 5 Risk conditions

Under 27C green Comfortable conditions

2732C yellow Fatigue possible with prolonged exposure

and/or physical activity

3241C orange Sunstroke, muscle cramps, and/or heat exhaustion

possible with prolonged exposure and/or physicalactivity

4154C red Sunstroke, muscle cramps, and/or heat exhaustion

likely

Heatstroke possible with prolonged exposure and/or

physical activity

Over 54C purple Heat stroke or sunstroke likely

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Figures4 and 5 report hourly heat index values of June, July and August 2003 and

1950, respectively. It appears that, during 2003 summer, the heat stress in June is elevated

only in the central hours of the day while becomes more intense during almost all day time

starting from the second half of July. Moreover, a mild heat discomfort conditions are

found to persist in night time during the two heat waves and to disappear only in the lastdays of the first week of July, marking the transition from the first to the second heat wave.

During 1950 summer, at least two heat waves are responsible for strong heat discomfort

conditions in the day time starting from the last three days of June up to the last week of

August; as in 2003 summer, a mild heat discomfort is found to characterise the night time

during July and August.

Table2shows that, during the 2003 summer, the mortality in person aged 75 years or

more in the city of Naples has been the highest of the last 10 years (Statistical Section of

Naples City Hall2005; Conti et al.2003) and this was probably due to the heat discomfort

and to the increased physical stress and dehydratation. Otherwise, the magnitude of heat-

related mortality might be notably greater than what here reported, since accepted criteria

for determining heat-related death are not yet available and heat may not be listed on the

death certificate as causing or contributing to death (Donoghue et al. 1997; Shen et al.

1998).

The results of the analysis on the secular variation of heat index over Naples during the

18722004 interval suggest that the apparent temperatures do not show any significant

Fig. 2 Summer maximum mean values of apparent temperature in Naples

Fig. 3 Mean value of apparent temperature recorded in Naples during summer from 1872 to 2004

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Fig. 4 Hourly apparent temperature recorded during summer 2003; the colours refer to those reported on

Table1 (colour only available in online version: dx.doi.org/10.1007/s11069-006-7963-y)

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Fig. 5 Hourly apparent temperature recorded during summer 1950; the colours refer to those reported on

Table1 (colour only available in online version: dx.doi.org/10.1007/s11069-006-7963-y)

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trend and that presumably the occurrence of heat waves, such as those of 2003 and 1950

summers, depend on the type of the summer circulation dominant over the Mediterranean

area.

References

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Aviation Medical Research Association Committee

Conti S et al (2003) La mortalitain Italia durante lestate del 2003, Igiene e SanitaPubblica, LX, 3:120122

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Table 2 Number of deaths

occurred in Naples in the

19952004 interval

Year Number of deaths

75 year-old or more

1995 1,094

1996 1,011

1997 1,057

1998 1,149

1999 1,080

2000 895

2001 1,186

2002 1,144

2003 1,405

2004 1,134

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