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What is the 'Ozone and heat plan' in Belgium and what are the different phases?

Context
In 2003, Europe was struck by an extraordinary heat wave. Because of the high temperatures and ozone concentrations, there was a sharp increase in morbidity and mortality in risk groups (elderly people, people with respiratory troubles).

In response to this heat wave, several countries set up action plans for heat waves in order to better control crisis situations like that in 2003. The goal of these plans is to be able to react quickly, in order to reduce the health impact of high temperatures and ozone concentrations on risk groups by taking appropriate measures.

In Belgium, it was decided to set up a national plan with thresholds for both temperature and ozone. Since summer 2005, this 'Ozone and heat plan' (further referred to as 'plan') was put in motion. The definition of heat wave in the current plan is not the same as the one used by climatologists.

The different phases of the plan

The plan consists of 3 phases, of which the second phase, the warning phase is further divided into two levels:

- a vigilant phase
- a warning phase, subdivided into levels 1 and 2
- an alarm phase

The warning and alarm phases are both started after a number of criteria are met. These criteria are based on results of 5-day weather forecasts, daily ozone measurements and 2-day ozone forecasts.

The first two phases of the plan, the vigilant and warning (level 1 and 2) phases are based on objective criteria (period, temperature and ozone concentration). The activation of the alarm phase, in contrast, requires additional assessment criteria (" the required actions for this phase are taken when the treshold has been reached and the measures already taken have to be intensified").


Before the alarm phase is activated, according to the original plan from 2004, a risk assessment group (RAG) is established. This RAG evaluates whether it is opportune to activate the alarm phase and if additional measures are needed. The suggestions and decisions of the RAG are then delivered to the risk management group (RMG) that is composed of representatives of the relevant authorities. The RMG eventually decides whether or not the alarm phase is activated. The heat and ozone criteria for the alarm phase have never been met since the start of the plan. Consequently, the RAG and RMG have also never been established in the framework of the current plan.

The thresholds of this plan are:

Temperature: a minimum temperature of 18°C and maximum temperature above 30°C, averaged for the period considered, measured in Uccle (RMI).

Ozone: the plan is based on the European information and alarm threshold as defined in the directive 2008/50/EC and are set at hourly mean concentrations of respectively 180 µg/m³ and 240 µg/m³.

 

 

The three possible phases of the plan are:

1. The vigilance phase

The vigilance phase starts on the 15th of May and ends on the 30th of September. From the 15th of May onwards, the actions are started systematically. As such, it is not dependent on a threshold, but on a period.

 

2. The warning phase

The warning phase consist of 2 levels:

Level 1
This level is solely based on meteorological criteria. It is reached when, based on meteorological forecasts, during a period of two days, following criteria are met:

- The mean minimum temperature (in the period under consideration) is higher than 18°C

AND

- The mean maximum temperature (in the period under consideration) is higher than 30°C

 

Level 2

This level is in effect as soon as the meteorological and/or the ozone criteria are met (both do not have to be met at the same time). This level is reached when, based on meteorological forecasts, during a period of three consecutive days, following criteria are met:

- the mean minimum temperature (of the 3 days under consideration) is higher than 18°C AND the mean maximum temperature (of the three days under consideration) is higher than 30°C

AND/OR

- on the previous day, in at least one measuring station, an hourly mean ozone concentration higher than 240 µg/m³ (EU limit value) is observed AND for the present day, for at least one measuring station, an hourly mean ozone concentration higher than 180 µg/m³ is forecasted (EU information threshold).

 

3. The alarm phase

- the mean minimum temperature (of the 3 days under consideration) is higher than 18°C AND the mean maximum temperature (of the three days under consideration) is higher than 30°C

AND

- on the previous day, in at least one measuring station, an hourly mean ozone concentration higher than 240 µg/m³ (EU limit value) is observed AND for the present day, for at least one measuring station, an hourly mean ozone concentration higher than 180 µg/m³ is forecasted (EU information threshold).

AND

- The measures already taken need to be intensified

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