This week, more than ten thousand ships are sailing in and around Amsterdam. SAIL is the largest freely accessible event in Europe, which brings challenges. As temperatures rise, concerns arise for the safety of participants and visitors at such events. The Safety Region Amsterdam-Amstelland has asked the KNMI to provide data for more than just temperature. How hot it feels for your body depends not only on air temperature but also on humidity, solar radiation, and wind. This is called heat stress.

The safety region can take action if a certain area is very busy and the heat stress is high.

There are various international standards that can determine the heat load on the human body. One of those standards is the Wet Bulb Globe Temperature (WBGT). The KNMI uses this standard for the development of heat stress. The KNMI provides maps of this WBGT during SAIL every 10 minutes to the safety region at a resolution of 1 by 1 kilometer. The safety region can then take action, for example, by regulating pedestrian flows if a certain area is very busy and the heat stress is high. The WBGT from the KNMI only provides a value. It is up to an organization to associate threshold values with this and determine which measures are taken at which value.

What is the WBGT? 

The WBGT consists of three components: 

• the wet bulb temperature (counts for 70%), which takes into account the cooling effect of sweating. Since sweating is a very efficient way to lose body heat, this component counts heavily.
• the black globe temperature (counts for 20%), which takes into account the effect of direct solar radiation on the body.
• the air temperature (counts for 10%), this is the temperature in the shade.

Since the wet bulb and black globe temperatures are not standardly measured at KNMI weather stations, they are calculated. The KNMI uses one of the international standard approaches that utilizes variables that are measured as standard, namely global radiation, relative humidity, wind speed, and air temperature.  

Product for the safety region 

To better monitor the area in Amsterdam around SAIL, a weather station (WOW station) has been set up on the roof of Vrije Universiteit. Together with the existing WOW stations and the official KNMI weather stations, high-resolution maps are created for various variables. These maps are available on the KNMI Data Platform. These maps, along with the global radiation from KNMI weather station Schiphol, are used to calculate the WBGT and make it available every 10 minutes for the safety region Amsterdam-Amstelland (see image 1 for an example).