In 2010 KNMI revised its weather alerts and warnings system, in close cooperation with private weather companies and social stakeholders (e.g. Dutch railways, automotive and crisis management organisations). One of the challenges during this revision was to clarify (and quantify) the direct links between extreme weather and its effect on society.
The Dutch meteorological observational network consists of 35 (surface) weatherstations, all fully automated. With a network this dense, the forecasters problem during severe weather is not the availability of meteorological observations. Direct feedback on the effects of severe weather (e.g. damage reports) can help the forecaster to assess the actual warning levels.
Thresholds for warnings in case of extreme weather are determined quantitatively for each weather parameter, most often defined by climatological return periods. However, these thresholds must be seen as best estimates, with non-meteorological factors influencing the final effects of the weather on society.
For example, the presence of a national holiday may have a significant effect on the number of caravans on the roads, increasing the risk of weather related accidents during events with high wind speed. Also, the timing and location of occurrence of a severe weather event will have a significant impact on the effect at society. Snowfall of 1-2 cm during traffic peak hours will block traffic largely, which will not be the case in rural areas at nighttime.
In the new KNMI weather alert and warnings system, the assessment of severe weather situation is done by KNMI in close cooperation with commercial weather companies and Dutch military. The (possible) effects of the extreme weather on society is discussed with social stakeholders, leading to a collaborative decision on the severity of the weather warnings.
More insight in the effects of severe weather is important for KNMI. To increase the knowledge on this, KNMI started a pilot with the collection of damage-reports during extreme weather. First, an application for mobile devices using Apple iOS was developed. In this application, during severe weather, users are asked to send reports of weather-related damage to KNMI. These reports contain a description of the event itself (events are not free to define, but predetermined by KNMI), time and location (GPS-based) of the event and a picture (optional). For further information, contact information of the contributor can be send. The reports are then collected by KNMI and presented to KNMI forecasters and KNMI communication staff.
The damage-reports are used to assess the actual warning level, to evaluate KNMI warning thresholds and may also be useful for specific research investigation of severe weather-related incidents.
The presentation will give more information on the KNMI warning system and elaborate on the mobile application itself and the results sofar.