Daily and hourly fire risk analysis — API

These services provide fire risk analyses for the current season per day and hour in real time. The daily API represents the fire risk in the afternoon when the fire risk is usually at its highest. The API per hour describes the fire risk hour by hour and thus shows the variation of fire risk during the day. In the APIs for fire risk forecasts, there are corresponding calculations in the future, when the fire risk on the day also depends on how the weather was before, especially with regard to the precipitation. SMHI’s work on fire risk calculations (forecasts and analyses) is carried out on behalf of MSB. Calculations of fire risk (forecast and analysis) are made only over land and lakes in Sweden. In both the daily and hour API, the Canadian Fire Weather Index (FWI) model* is a well-used model both inside and outside Europe. The FWI model is also part of a larger model system for assessing fire risk and behaviour called Canadian Forest Fire Danger Rating System (CFFDRS)**. At SMHI, the daily variant of the FWI model was introduced in 1999. The FWI model describes, among other things, fire behaviour, spreading speed and the amount of fuel available for the fire in various variables. The daily input data of the FWI model are the weather parameters temperature, relative humidity and wind 12 UTC and precipitation 18-18 UTC, from MESAN. The input data for the hourly variant of the FWI model is instead temperature, relative humidity and precipitation for every hour from MESAN. The differences between the daily and hour variations of the FWI model: — The hourly variant uses inputs from the daily variant for (DMC, DC, BUI) as these variables do not vary significantly during the day. — In the hourly variant, moisturisation/drying speeds are faster than in the daily variant. The first 0.5 mm is ignored in the daily variance, but the hourly variation includes all precipitation. — Since the model set and input data for the daily and hour variants are not the same, the different FWI models will get different values even for the time 12 UTC. In addition to the FWI model variables, the hourly API also contains: — grass fire risk in the old last year’s grass — potential rate of spread of a fully developed grass fire in uncut and unmoved last year grass (m/min) (Rn) global radiation in W/m² (GLirr) In addition to the FWI model variables, the daily API also contains: —fuel dehydration indicating how dehydrated it has become both in the fuel and in the soil layers most important in forest fires. —grass fire risk in the old last year’s grass fire model on a daily basis — the potential rate of spread of a fully developed grass fire in uncut and unmoved last year grass (m/min) (Rn) according to the grass fire model on a daily basis. The daily model*** for grass is based on the hourly model**** and uses temperature, precipitation, relative humidity, wind and global radiation (solar radiation) as input. The daily model represents the highest grass fire risk during the day, unlike the hourly model, which instead describes the grass fire risk for each hour. * Development and structure of the Canadian Forest Fire Weather Index System. 1987. Van Wagner, C.E. Canadian Forestry Service, Headquarters, Ottawa. Forestry Technical Report 35. 35 p. https://cfs.nrcan.gc.ca/publications?id=19927 ** https://cwfis.cfs.nrcan.gc.ca/background/summary/fdr *** will come later **** A new model for grass fire hazard (2021) Sjöström, J., Granström, A, Jansson, A and Böhlin, J https://rib.msb.se/filer/pdf/29530.pdf