Climate Exchange

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ealth

For Germany’s HHWS the meteorological statistics had to be

linked with the mortality data, which were available for Baden-

Württemberg, for different European cities outside Germany

(Budapest, London, Lisbon and Madrid) and for the Netherlands due

to DWD’s participation in the European cCASHh-project. The goal

was to estimate excess mortality as a function of the heat load, and

this required mortality statistics to be corrected for changes in popu-

lation and the annual cycle. For all analysed mortality time series,

on days with a strong or higher heat load, mortality was increased

by 10 per cent or more. When selecting the threshold value for

issuing warnings and triggering interventions, various aspects must

be considered: too frequent warnings will lead to warning-fatigue,

while if warnings are too rare users might forget what they ought to

do. So we used days with a strong (category +3) or extreme (category

+4) heat load to trigger heat warnings in Germany. Within the 36

analysed years, 121 days fell within these categories.

Germany’s HHWS is based on a combination of DWD’s weather

forecast output and a health-related assessment of the thermal envi-

ronment. The latter combines a complete heat budget model with a

short-term adaptation approach.

Four fundamental meteorologi-

cal factors are needed to assess the human thermal environments:

air temperature, mean radiant temperature, humidity and wind

velocity. In addition, physiological parameters like the metabolic

rate or weight and clothing worn by a person are needed to assess

the thermal load. Since no information is available about an indi-

vidual’s physiological parameters, the assessment is made for a

standardized person. DWD uses a complete heat budget model of

the human body, which takes into account all relevant mechanisms

of heat exchange with the atmospheric environment. Heat exchange

is modelled for a standard male, known as ‘Klima-Michel’, who

chooses his clothing to maintain thermal comfort as far as possible.

Based on the calculated perceived temperature (PT),

nine physi-

ological stress categories from ‘extreme cold stress’ to ‘extreme heat

load’ have been defined.

Warnings are issued for ‘strong heat load’ and

‘extreme heat load’ periods of at least two consecutive

days. On each day, when the PT at 12 Universal Time

Coordinated exceeds a threshold of around 32° C, a

warning is issued by DWD at about 10am covering a

two-day period. The warning threshold is not fixed. It

takes into account that humans adapt to their thermal

environments and can cope better with heat if they are

used to it. Therefore the thresholds are a bit higher

in Germany’s warmer regions and in late summer.

An additional requirement for a warning to be issued

is that night-time temperatures stay above a certain

threshold (15-18° C), as high minimum temperatures

prevent people from recovering sufficiently.

While DWD is responsible for the meteorological

component of the HHWS, partners are needed to make

sure the information reaches those who need it most

– elderly and very young people – and to introduce a

set of interventions. Due to the federal structure of the

German health system, these partners are the respective

federal health authorities and DWD had to negotiate

and sign contracts with all 16 Federal Laender (federal

states) to make sure the warnings get through. In some

Laender, interventions vary between a warning for a

‘strong’ and an ‘extreme’ heat load. For DWD however,

the communication strategy remains the same inde-

pendent of the level of warning.

Warnings are issued for all counties across

Germany during the warm season (typically May to

September), for six different altitude categories in

line with DWD’s general warning strategy. Before a

heat warning is issued, the automatically-generated

warning guidance is reviewed by a biometeorologist.

In addition to the information from the heat stress

model, a building simulation model provides infor-

mation about indoor conditions.

All the HHWS warnings are issued to the general

public through the DWD warning platform on the

Internet, and are accessible through the multilingual

Meteoalarm platform. Newsletter systems are also

available for the general public and elderly care and

nursing homes. The relevant health and supervisory

authorities are directly notified; they are responsible

for defining and monitoring the implementation of

intervention measures. They also have the option of

broadcasting the warning more widely to the public

on radio and television.

Administrative challenges

Among DWD’s duties is “the provision of meteorologi-

cal services for the general public or for individual

customers and users, especially in the fields of …

public health.”

It also includes regulations on remu-

neration. In general “The Deutscher Wetterdienst

shall charge a remuneration for the provision of its

services.”

The aim was to provide the HHWS service

free of charge, so a series of internal discussions was

needed to establish that this type of service is an essen-

tial product and can be part of DWD’s Global Data

Image: Thomas Max Müller/pixelio.de

Warnings call on the public to behave heat-related